without respect to the length of the rod we may drive the key home as in
Fig. 2404, and mark on it a line coincident with the edge A of the
strap. We then lift the key up to its proper height and mark a second
line, so that when removed from the keyway the key will have on it the
two lines shown in Fig. 2405, A being the first and B the second line;
and the difference between the width of the key at A and its width at B
will be the thickness of the liner necessary to be placed behind the
brass nearest to the key. To ascertain the precise amount of this
difference (because a very small error as to this amount causes a great
deal of extra labor), we set a pair of outside calipers to the width at
A; and then passing the caliper points down to B, we keep one of the
points even with the line B, and insert a wedge until it just fills the
space between the other point and the side of the key, as shown in Fig.
2406, C being the wedge, which should be chalked along its surface so
that, when inserted until it touches against the caliper point, the
latter will leave a mark on the wedge, denoting exactly how far the
wedge entered, and hence the exact required thickness of liner.
[Illustration: Fig. 2407.]
[Illustration: Fig. 2408.]
It has thus far been supposed that the joint faces of the brasses are
made to come brass and brass, that is to say, butt close together from
the key pressure, when the brass bores properly fit the journal.
Suppose, however, that the joint of the brass is left open as in Fig.
2407, and in that case a strip of metal F, whose diameter equals that of
the journal, may be inserted between the brasses as shown, and at its
centre should be provided a small centre-punch mark, denoting the centre
of the bore. A piece of this kind should be inserted in the brasses at
each end of the rod and placed in the middle of the length of the bore,
the centre-punch marks being to apply the trammels to. Or if the rod was
made of correct length when new, and the bore of the brasses, therefore,
requires to stand central in space F, Fig. 2403, then the pieces F, Fig.
2407, may be dispensed with by marking a line B, Fig. 2408, central to
space F, Fig. 2403. Then put the strap on the rod (with the brasses,
gib, and key in place), and pull the strap back to hold the key up to
its proper height.
[Illustration: Fig. 2409.]
The two brasses should then be placed as far apart as possible in the
strap, each bedding fairly against its back or crown. Then, using the
joint face of the back brass as a straight-edge or guide, a line should
be marked on the side face of the strap, this line representing the
position of that face when the brass is bedded fairly home, and being
shown in Fig. 2408 at A. This brass should then be moved forward until
the bore of the pair of brasses at D, Fig. 2408, measures equal to the
diameter of the journal (of the crank pin or of the cross-head pin as
the case may be) and a second line B, also coincident with the joint
face of the brass, should be marked upon the strap, and the strap will
then have marked on it the two lines shown in Fig. 2409, in which it is
shown removed from the rod; the distance apart of these two lines will
be the thickness of the two liners combined, hence half this thickness
will be the thickness necessary for each liner. Suppose, however, that
it is not known whether the rod has been correctly made, and therefore
it be unknown whether, in order to have the rod of the correct length,
the brass bore should stand in the centre of the space or not.
This is often the case in repairs, and sometimes on new rods, in which
slight inaccuracies of workmanship are apt to occur. In this case it is
best to mark a line, as G, in Fig. 2410, representing at each end of the
rod the centre of the space F in that figure. Then set a pair of
trammels to the correct length of the rod, and with one point of the
trammel resting on the point at the intersection of line C with line D
(the latter being the line G transferred to the centre of the bore) at
the small end of the rod, we mark a line at the other end. If the lines
D are too far apart, making the rod too long, the trammels will mark a
line R, and the distance between lines R and D at the large end will be
the amount the rod is too long, while half this distance will be the
thickness of liner to go behind each bottom brass if the error of length
is to be equally divided between the two ends of the rod, in which case
a line T, midway between D and R, must be marked, the trammel then being
rested on T, and the line S marked. These two lines, S and T, are then
the centre lines for the bores of the brasses.
[Illustration: Fig. 2410.]
If it is determined that one pair of brasses shall be central in its
space F, all the error being thrown on the other pair, this may be done
by lining one pair up so that its bore is true to line D, and putting
behind the back brass at the other end a liner whose thickness is equal
to the distance between D and R at the large end of the rod. It is
obvious that the measurement for rod length must be taken on the line C.
Having thus determined what thickness of liner is necessary to bring the
rod to its proper length, it remains to find the thickness of liner
necessary for the other half brass, to bring the key up to its proper
position, the process for which has already been explained. After,
however, the various liner thicknesses have been found, and the sheet
metal selected to cut them from, it is well to try if the thickness is
correct by cutting off a small piece of the metal, putting it in place
behind the brass, and then, after keying up the brasses, the rod length
may be trammelled.
As the liners placed behind connecting-rod brasses require to be very
finely bedded, the facility with which their forms permit them to be
fitted is an important consideration.
[Illustration: Fig. 2411.]
In Fig. 2411 is shown the forms commonly given, the requisite form of
liner being shown beneath each. Form 1 will bed very firmly to its seat,
but it will be observed that its liner is a difficult one to make, the
bottom section A being thicker than the sides or wings B. This is a
troublesome form of liner to fit as well as to make. If it be made of
wrought iron, the wings B must be either forged or filed to their
reduced thickness.
In the form at 2 in the figure we have the same defect, while in
addition the liner will not adjust itself so readily in position to its
bed.
This latter is an easier form to make in the moulding pattern, and
easier to mould, and somewhat easier to fit, but it is not so firm as
the first. To cause this form of brass to bed easily to its proper
position it is sometimes given a lug on the bottom, as at 3 in the
figure, the lug extending part of the width across only, because if it
extended fully across, the liner would require to be in two pieces,
causing trouble both in fitting them and in getting them into their
places. When the lug extends partly across, the liner must have a slot
to pass over and admit the lug, and this causes trouble in bending the
liner to the required curve.
In the form shown at 4 in the figure all these difficulties are avoided,
while, if the lower corners are made square instead of rounding, a
simple piece of sheet metal will serve as a liner requiring but little
fitting and bedding if it be of the proper thickness.
[Illustration: Fig. 2412.]
To fit up a link motion, assuming the machine work to be done, the first
thing to do is to face up the side faces of the links, making them
parallel, and true to a surface plate. The slot is then filed out square
to the side faces, its curve being filed to a template T, Fig. 2412,
which is provided with a piece of wire for a handle. It is supplied with
red marking, and is rubbed upon the slot to mark the high spots. The
same template may be used to prepare the link block or die; but as soon
as the block can be moved in the slot with slight hammer blows (using a
mallet or a block of wood) it should be used instead of the template,
the bearing marks serving to correct and finish the block as well as the
slot. In filing up the block care should be taken to make it of even
thickness on each side of its hole and with its sides parallel to the
hole, the latter being of great importance. When the block is a
sufficiently easy fit in the slot to permit it, a round stick of wood
may be put through it and used to move it up and down the link slot for
the marking process.
The next operation is to fit the eccentric rod eyes to the link, and to
then ream out the holes in both the link and the eyes while they are put
together. The block may then be placed in the link, and the rocker pin
passed through the block and into the rocker arm, so that the working
fit of these parts when put together may be tested and adjusted if
necessary. The link hanger may then be fitted to the saddle pin, when
the whole will be ready for the file finishing and polishing, after
which it may be case-hardened.
CASE-HARDENING.--Case-hardening consists in the conversion of the
surface of wrought iron into steel, or in converting the grade of a low
steel into a sufficiently high grade to render it capable of hardening.
The depth to which this conversion occurs depends upon the material used
to produce it, and the length of time the process is continued, varying
from 1/64 inch under the prussiate of potash process to 1/16 or 1/8 inch
in the case of long-continued box case-hardening.
Work that is thoroughly case-hardened has a dull white, frosted-looking
surface. If the surface of the work is mottled, or has patches of fancy
water-mark colors, it may be hard, but it is not so to the highest
attainable degree.
To thoroughly test this, take a new dead-smooth file and apply its
corner edge under heavy pressure to the work on an edge where the fancy
colours are, and then on an edge where the surface is white, and the
latter will be found to be the hardest as well as hardened the deepest.
The simplest method of case-hardening is by the prussiate of potash
process, for which it is essential that the prussiate of potash be
finely powdered, and contain no small lumps. The piece being heated may
then, if small, be dipped in the prussiate of potash, or if large have
the same spread upon it. In either case, however, the work must be hot
enough to cause the potash to fuse and run over the work surface, and
this action may be assisted by using a piece of iron wire, spoon-shaped
at the end, wherewith to apply potash to the work and rub it upon the
work surface.
After the potash has thoroughly fused and run over the entire surface of
the work it will usually have become somewhat cooled, and will require
reheating before quenching in the water.
If this reheating be done in the blacksmith's fire, it is not well to
put the blast on; it is better to let the blast on gently while applying
the potash to the work, so as to have a live clear fire to put the work
in, and reheat it with the blast turned off.
While the work is in the fire it should be constantly rotated, not only
to heat it evenly, but to let the adhering potash run over the entire
surface, and as soon as the required heat is attained the work should be
removed from the fire quickly and quenched in water.
It may be added, however, that if after the potash has been applied and
fused more potash be added, so that it will adhere to the work and not
fuse until the work is put into the fire a second time, then, after the
work is quenched and taken from the water, there will be found on it a
thick white and closely adhering fur of melted potash, and the work will
be a dead white, with no fancy colors on it, and as hard as it is
possible to make it.
The prussiate of potash process is, of course, from its expensiveness,
both in material and labor, too costly for work to be done in
quantities, and box-hardening is therefore resorted to.
In box case-hardening the work is case-hardened all over. It consists in
packing the work in an iron box containing the hardening material, and
subjecting the whole to a cherry-red heat for some hours.
A very common process is to fill a sheet-iron box with the work closely
packed about with bone-dust, the pieces of the work having at least a
thickness of 3/8ths of an inch of bone-dust around them. The seams of
the box are well luted with clay to prevent the gases from the consumed
bone-dust from escaping, and to exclude air.
Various ingredients are used to effect case-hardening. One process is as
follows: 20 lbs. of scrap leather and 15 lbs. of hoofs (cut into pieces
of about an inch square), 4 lbs. of salt, and one gallon of urine are
prepared, and a wrought iron box with a lid capable of being fastened on
is obtained. The fastenings must be capable of ready unfastening when
hot. A layer of leather and pieces of hoofs about 1-1/2 inches thick is
first laid in the box, then a layer of salt, and then a layer of work.
Leather and hoof are then packed closely around the work and above it
for a thickness of about an inch, and a second layer of work added, and
so on, the last layer being of leather, &c., completely filling the box;
the urine is then added, and the box well sealed with clay.
The box is placed in a furnace and kept at a red heat for about fourteen
hours, and is then taken to a deep tank, and the work quickly immersed,
so as not to be exposed to the air after the box is opened.
If the pieces are of solid proportions, so as not to be liable to bend
or warp in the cooling, the contents of the box are simply dumped into
the tank, the water being allowed to flow freely in the tank to keep up
a circulation and cool the work quickly; some work, however, requires
careful dipping to prevent it from warping. Thus a link or a double-eye
would be dipped endwise, a plate edgewise; but all pieces should be
immersed as quickly as possible after the box is opened.
Sheehan's patent process for box case-hardening, which is considered a
very good one, is thus described by the inventor:
DIRECTIONS TO MAKE AND USE SHEEHAN'S PATENT PROCESS FOR STEELIFYING
IRON.
No. 1 is common salt.
No. 2 is sal soda.
No. 3 is charcoal pulverized.
No. 4 is black oxide of manganese.
No. 5 is common black rosin.
No. 6 is raw limestone (not burned).
Take of No. 1, 45 lbs., and of No. 2, 12 lbs. Pulverize finely and
dissolve in as much water as will dissolve it and no more--say 14
gallons of water in a tight barrel; and let it be well dissolved before
using it.
Then take three bushels of No. 3, hardwood charcoal broken small and
sifted through a No. 4 sieve. Put the charcoal in a wooden or iron box
of suitable size made water-tight.
Next take of No. 4, 5 lbs., and of No. 5, 5 lbs., the rosin pulverized
very fine. Mix thoroughly No. 4 and No. 5 with the charcoal in your box.
Then take of the liquid made by dissolving No. 1 and No. 2 in a barrel
as stated, and thoroughly wet the charcoal with the whole of said
liquid, and mix well.
The charcoal compound is now ready for use.
A suitable box of wrought or cast iron (wrought iron is preferable)
should next be provided, large enough for the work intended to be
steelified.
Now take No. 6, raw limestone broken small (about the size of peas), and
put a layer of the broken limestone, about 1-1/2 inches thick, in the
bottom of the box. A plate of sheet iron, one-tenth of an inch in
thickness, is perforated with 1/4-inch holes one inch apart. Let this
plate drop loose on the limestone inside the box. Place a layer of the
charcoal compound, two inches thick, on the top of said perforated
plate. Then put a layer of the work intended to be steelified on the
layer of charcoal compound, and alternate layers of iron and of the
compound until the box is full, taking care to finish with a thick layer
of compound on the top of the box. Care should also be taken not to let
the work in the box come in contact with the sides or ends of the box.
Place a suitable cover on the box and lute it with fire-clay or yellow
mud. The cover should have a quarter-inch hole in it to permit the steam
to escape while heating.
The box should now be put in an open fire or furnace (furnace
preferred), and subjected to a strong heat for five to ten hours,
according to the size of the box, and the bulk of iron to be steelified.
Remove the pieces from the box one by one and clean with a broom, taking
care not to waste the residue, after which, chill in a sufficient body
of clear, cold water, and there will be a uniform coat of actual steel
on the entire surface of the work to the depth of 1/16 or 1/8 of an
inch, according to the time it is left in the fire. The longer it is
left in the fire the deeper will be the coat of steel.
Then remove the residue that remains in the box, and cool with the
liquid of No. 1 and No. 2, made for the purpose with 20 gallons of
water, instead of 14 gallons, as first used with the charcoal compound.
The residue must be cooled off while it is hot, on a piece of sheet iron
or an iron box made for the purpose. Turn the residue into the supply
box, and it will be ready for use again. The more it is used, the better
and stronger it will be for future work.
There is nothing to be renewed for each batch of work but the limestone,
and that, after each job, will be good burned lime.
A process used at the Elevated R.R. shops in New York city is as
follows: The materials used are: leather, 1 part; bone dust, 5 parts;
salt, 1 part. Heat for 48 hours to a red heat in a box sealed with fire
clay, and quench in a solution of 3 pounds of potash to 30 gallons of
water.
The wrought iron thus treated is impervious to a new smooth file at a
depth of 1/16 of an inch.
The potash water is said to prevent both warping and the formation of
blister marks on the work.
The durability of work case-hardened is greatly enhanced, but it is an
expensive process; not so much by reason of the cost of it, but because
it involves resetting and a refitting of the parts. The resetting is
necessary because the work warps under or during the process. This
warping can be prevented to some extent by placing the heaviest pieces
in the bottom of the box, and so packing the same that the weight of the
top pieces shall not tend to bend those beneath them when the hardening
material has burned away, and so placing the upper pieces that they
shall not be bent by their own weight. Thus both in packing and locating
the work in the box the utmost care is necessary.
SETTING WORK AFTER HARDENING IT.--Work that has been hardened or
case-hardened usually swells during the hardening process, and therefore
requires refitting afterwards. This swelling usually occurs in all
directions, thus holes and bores become of smaller dimensions, while the
outside dimensions also increase, bolts become of larger diameter and
sometimes increase in length.
In very exceptional cases, however, the dimensions of a piece of work
will not alter.
This renders it usually necessary to refit the work after it has been
hardened, thus holes which are ground out by laps or bolts may be ground
to diameter in a grinding lathe.
In some practice, however, the work to be hardened is made a somewhat
too easy fit, the holes tapped out and the bolts ground in by direct
application of the bolts to their holes in connection with flour emery
and oil. This latter plan is also adopted for forms not easily ground
out in a machine, as, for example, a die in a link of a link motion.
[Illustration: Fig. 2413.]
[Illustration: Fig. 2414.]
To prevent surfaces or forms of this class from altering their shape or
dimensions during the hardening process, slips of iron are sometimes
fitted to them before they are placed in the hardening box. Thus Fig.
2414 represents a double eye, and Fig. 2413 a link having thin pieces
fitted in as shown at A in both figures.
The heating for the hardening process is also apt to impair the
alignment of the work, causing it to require resetting by the aid of
parallel strips and straight-edges.
[Illustration: Fig. 2415.]
The faces of the link having been set, the width of the link slot must
be set, for it may open or close in places. If it opens it may be closed
by the jaws of a powerful vice, while if it closes it may be opened by a
pair of inverted keys, inserted as shown in Fig. 2415, and driven in by
the hammer. At each trial, however, a mark should be made on the driven
key, so that it may be known how far to drive it at the next trial.
[Illustration: Fig. 2416.]
[Illustration: Fig. 2417.]
Fig. 2416 represents a link that is supposed to have been case-hardened,
and to therefore require resetting. The stem from A to B should first be
straightened to a straight-edge on both its side and edge faces. It
should then be tested for winding with the winding strips, C, D, placed
as in Fig. 2416, and then as in Fig. 2417.
[Illustration: Fig. 2418.]
[Illustration: Fig. 2419.]
To test the alignment of end E, press a straight-edge S fair against its
side face, as in Fig. 2418, and measure the distance H. Then place the
straight-edge on the other side face of E and measure the distance I,
Fig. 2419, and these distances both measuring alike, E will be true
providing that the jaws at end F have not altered from their proper
width apart.
To test the alignment of the jaws at end F, press a straightedge against
the outside face of the hub and measure the distance J, Fig. 2420, then
apply it on the other side and measure distance K, Fig. 2421, and when
distances J and K are equal and the width L between the jaws is correct,
end F is in line in one direction. To test it in the other direction,
apply a pair of parallel strips, placing one on end E as in Fig. 2417,
and the other across the face of the hub of end F to see if there is any
twist.
[Illustration: Fig. 2420.]
[Illustration: Fig. 2421.]
Suppose, however, that distances J K are unequal, then if distance L is
too narrow (when tested by the piece that fits between the jaws) then
the jaw at F that gives the widest distance at E is the one that
requires correction, or if distance L is too wide, the jaw that shows
the least distance at end E is the one requiring correction.
The link should be warmed to about 300°, or nearly _black_ hot, and
pieces of sheet copper placed between the work and the anvil, and
between the blacksmith's tools and the work, so that the latter may not
be bruised by the blows delivered to effect the straightening.
After the process has been performed at each end individually the
testing should be repeated, because setting the end F may have impaired
the setting of end E, in the alignment to F.
It is obvious that the same setting or aligning process would be
required in the case of a large link, where the ends were forged
separately and welded to the body after the machine work and fitting had
been done to them.
[Illustration: Fig. 2422.]
[Illustration: Fig. 2423.]
[Illustration: Fig. 2424.]
[Illustration: Fig. 2425.]
[Illustration: Fig. 2426.]
FITTING BRASSES TO BOXES OR TO PILLAR BLOCKS.--In the operation of
fitting brasses to their boxes or to pillar blocks there are two things
to be especially guarded against: First, having the brass let down
one-sided, as shown in Fig. 2422; and next, aslant, as shown in Fig.
2423. The first depends on taking the proper amount off the two side
faces, and the second in cutting the inside of the flanges fair. To cut
the side faces fair, grip the brass in the vice, as shown in Fig. 2424
(the brass being shown in section), in which a is A block of wood. Take
the measure of the box, down where the brass will come when home, and,
if there be any taper to the box, set the inside calipers to the top of
the location for the brass, and after the brass is in the vice place a
square under one side-face, as at B in Fig. 2426, and see how much there
is to come off. This saves the use of outside calipers, and is better
because, not only is the trouble of setting the latter avoided, but the
inside calipers can be tried to the box and the work in an instant, and
a correction can at once be made if the calipers have got shifted. The
cape chisel, or cross-cut, as it is sometimes termed, should first be
used, taking a cut close to the flange, and making it half as deep as
the calipers (applied as shown in Fig. 2426) show there is metal to come
off. Then a similar cut should be taken close to the other flange,
especial care being taken to take both cuts equally deep, and leaving
as much to come off the other side face of the brass; otherwise, the
brass will come atwist. Then take a straight-edge, and, placing its edge
fair with the two chisel-grooves, while holding it firmly against the
joint face of the brass, mark a line running from one chisel groove to
the other; this line serving as a guide for the depth of all the other
cape-chisel grooves. Now cut off the intermediate spaces with the flat
chisel, using a straight-edge as a guide. If the box is taper, chip the
side face to a corresponding taper, using a bevel-square, or estimating
the amount by the eye if it is not too much. Now file the chipped
surface flat and true, and then turn the brass upside down, gripping it
with the wood as before, and dress the other side face (applying the
inside calipers as in Fig. 2426), and bring that face down to within
about 1/64 inch of the size to which the calipers are set. If the block
of wood is made a little shorter than the length of the brass, the
calipers can be applied without moving the brass from or in the vice.
The method of applying the square to these side faces is shown in Fig.
2425, in which A is the brass in section, B a straight-edge, and C a
square.
[Illustration: Fig. 2427.]
[Illustration: Fig. 2428.]
[Illustration: Fig. 2429.]
[Illustration: Fig. 2430.]
We now turn our attention to the flanges, and apply a square to the
crown of the box, bringing the edge of the blade fair with the edge of
the box, as shown in Fig. 2428, A representing the box in section, and B
the square. Supposing the crown of the box to stand square, as shown in
the engraving, and as it should do, we set the brass upon a
truly-surfaced iron plate and square up the joint face, as shown in Fig.
2427, in which A is the surfaced iron, B the brass, and C the square.
Since, however, the joint face of the brass may not be parallel with the
crown face, we may place the square so that its blade edge comes fair
with the crown face--that is, as shown at D in Fig. 2427--and set the
brass crown (by means of inserting a wooden wedge under its face) truly
perpendicular or parallel with the square blade edge. Now try the square
with the side face of the brass, setting the latter true with the square
blade, as in Fig. 2430; A being the iron plate and B the square; and,
supposing the box to be true, as it usually is, we may set a
scribing-block, as shown in Fig. 2427, and mark off how much is to come
off the flanges by scribing a line around the flange, sufficiently
depressing the scriber-point to allow an equal amount to come off each
of the flanges. Sometimes, however, the inside faces of the box are not
true with the outside face. To test this, we place a straight-edge
across the outside face, place a square on it, and apply it to the
inside face of the box, as in Fig. 2429, which is a plan view of the
box, A being the straight-edge and B the square. If the square thus
applied shows a want of truth in the box, we may set the brass over when
adjusting it (as in Fig. 2427) to a corresponding amount, and thus mark
off the flanges to suit the box.
[Illustration: Fig. 2431.]
To hold the brass while operating on the flanges, we resort to the
device shown in Fig. 2431, in which A is a bolt, B the brass, C a piece
of hard wood, and P a clamp fastened down by a nut D. To sustain the
plate P, so that it shall not fall down on the piece of wood every time
the brass is taken out to try it in the box, we may insert the spiral
spring S, shown in the separate view of the bolt, nut, and plate. One
such holding device will do for different sizes of brasses, by either
gripping the bolt lower down in the vice jaws or putting washers between
the nut and the plate. This will hold the brass very firmly, and at the
same time leave the whole of the flange easily got at. When the flanges
are dressed, we may try the brass in the box, putting red-lead marking
on the box to mark where the brass binds. While letting the brass down,
however, we must be careful to let it down fair, to avoid the state of
things shown in Figs. 2422 and 2423. A ready method of doing this is
(supposing the box to be true, as it should be, and making the necessary
allowance if it is not), to set a pair of inside calipers to the joint
face of the brass and the top of the box, as shown in Fig. 2432, trying
the calipers (in the two positions there shown) on both sides of the
box. This should be done every time the brass is tried in the box, until
such time as the brass begins to bed against the bottom of the box.
[Illustration: Fig. 2432.]
We now come to the bedding of the brass to its seat in the box. This
requires skillful treatment; for one mistake will involve a great deal
of extra work to rectify it.
In fitting the brass to the box care must be taken to leave it a rather
tighter fit to the box than it requires to be when finished, that is
after the bore has been made, because in the boring operation the sides
of the brass are apt to close and loosen the fit of the brass to the
box.
[Illustration: Fig. 2433.]
When the side faces and flanges are so far fitted as to render probable
the brass driving home at the next trial, the bed of the box should be
given a coat of red-lead marking, and small pellets of stiff red lead or
putty should be stuck on the bottom of the box, two at each end of each
bevel, and two at each end of the bottom, with one in the middle of the
bottom and each bevel, as shown at A, B, C, D, E, F, in Fig. 2433, by
the black spots. Then when the brass comes home, it will flatten these
pellets, and their thickness (when the brass is taken out) will show how
much the bevels are out, and how much to take off the brass to make it
bed. These pellets _must_ be restored to their original shape every time
the brass is tried; otherwise, they may mislead. To insure their
sticking to the box, and not coming out with the brass, the bottom of
the box must have red-lead marking kept upon it. The chipping should
continue until the pellets flatten out equally on the two bevels, but
are left a little thicker on the bottom. If this is not done, the bottom
will bed first, causing a great deal of extra filing, because filing the
side bevels will let the bottom down too far.
In driving the brass in and out of the box while fitting it, a piece of
wood must be used to strike on, otherwise the brass will stretch during
the fitting and come loose in the box during the boring.[33]
[33] See remarks on Pening, p. 162.
[Illustration: Fig. 2434.]
[Illustration: Fig. 2435.]
The patterns from which the castings for brasses are moulded should not
be made of the same angle or sweep on the bedding part or bottom as the
bottom of the box, pedestal, or pillar block, because the brass casting,
in cooling in the mould, contracts across the bore; thus if in Figs.
2434 and 2435 the full lines denote the shape of the pattern the dotted
lines denote the shape the casting will be.
[Illustration: Fig. 2436.]
[Illustration: Fig. 2437.]
The result of this is that when the brass is let down in the box it will
bed on the crown and not at the sides. Thus in Fig. 2436, A is a
pedestal, and B a brass which beds at C, but not at D or E. In Fig. 2437
is shown an example of a brass, with a circular bottom, which would bed
at the crown C, but not at the sides D E, until the metal was cut down
to the dotted circle F.
The amount to which this contraction in the mould occurs varies with the
size of the brass, the difference in the thickness at the crown and at
the face joint, the composition of the metal of which the casting is
made, and the temperature of the metal when poured into the mould. It
should always be allowed for, however, for the following reasons.
Referring again to Fig. 2436, it will be noted that it requires a heavy
cut off C to bring E, D to a bearing, while it is apparent that if the
brass met the box at E, D before it did at C, but little filing at E, D
would let the brass down a long way. It saves work, therefore, to so
make the pattern as to insure that the brass casting shall have bedding
contact at D and E before it does at C. As an example of the allowance
to be made for this purpose, it may be stated that in brasses of 6
inches bore and 9 inches long, the hexagon of the brass pattern at D, E,
Fig. 2436, would require about 1/16 inch put on them to compensate for
the contraction, supposing that the hexagon on the brass pattern were
made at first to fit the hexagon of the pedestal or axle box.
To originate a true flat surface we proceed as follows: In the absence
of a standard plate to go by, we must have three plates, and one of them
must be accepted as a provisional or temporary standard. This we will
call No. 1, and we fit Nos. 2 and 3 to it and then try them together,
and if they also fit it is proof that No. 1 was true, and that all three
are therefore true. It will very rarely happen, however, that this is
the case; but Nos. 2 and 3 merely serve to show how much No. 1 was out
of true.
Suppose, for example, that No. 1 is concave in its length, and we fit
No. 2 to it, as in Fig. 2438, and then fit No. 3 to it as in Fig. 2439,
and when we come to put Nos. 2 and 3 together, as in Fig. 2440, we find
that they are out of true to twice the amount that No. 1 is, and that
all the work that has been done to them to fit them to No. 1 has been
thrown away, and possibly to make them worse instead of better. It
becomes important therefore to select the most true plate for No. 1, and
this we may do as follows:--
[Illustration: Fig. 2438.]
[Illustration: Fig. 2439.]
[Illustration: Fig. 2440.]
[Illustration: Fig. 2441.]
[Illustration: Fig. 2442.]
If we have a straight-edge that is known to be true, we may lay it on
the face of a plate and move it laterally from each end alternately, and
if it swings from the centre the plate face is rounding, while if it
shuffles across moving first at one end and then at the other the face
is hollow; but if it glides as it were across, the surface is nearer
true. The straight-edge must not be pressed to the plate, but merely
touched laterally to make it move laterally, for if we take a true
straight-edge and press it vertically to a true surface while moving it,
it will show the marks of contact the most plainly immediately beneath
the parts where it is pressed. Selecting by this means the two plates
that appear to be the most true we proceed to test them further as
follows: We give to one of them which we will call No. 1 a light coat of
red marking, and placing it upon the other or No. 2, we move it about in
all directions and then take the two apart to examine the bearing marks.
Suppose then that No. 1 shows the bearing marks to be at the shaded
places, A and B, in Fig. 2441, while the bearing marks on No. 2 are as
at the shaded parts A and B in Fig. 2442, the two ends A having been
placed together; then we know that B is a high spot on No. 1, and A a
high spot on No. 1 for the following reasons. The marks at A, No. 2,
have been made by the marking at A on No. 1, and will extend across No.
2, a distance depending upon how much No. 1 has moved across No. 2, for
if corner A of No. 1 had only moved half-way across No. 2, it could only
have marked half-way across it. Similarly spot B on No. 1 has marked
spot B in No. 2, because it has been moved all the way across, it being
evident that the marking on B, No. 1, can only mark plate 2 as far
across its width as it is moved across it. From this it follows that the
higher or more prominent a spot is the less will be the area of the
bearing mark at that spot.
[Illustration: Fig. 2443.]
[Illustration: Fig. 2444.]
Now suppose that the two plates were curved to an equal degree as in
Fig. 2443, and the bearing marks would extend all over both surfaces;
but we may discover this error by turning one plate at a right angle, as
in Fig. 2444, in which case the bearing marks would show along the edges
of No. 1 and along the middle of No. 2, and we may correct each with the
file until both plates mark all across and from end to end when tried
together lengthways as in Fig. 2443, and one across the other as in Fig.
2444. But the plates may be curved to a different degree, as in Fig.
2445, and it then becomes necessary to know which to file the most in
correcting them and fitting them together, which we may discover as
follows:--
[Illustration: Fig. 2445.]
[Illustration: Fig. 2446.]
[Illustration: Fig. 2447.]
We give one plate a light coat of red marking and rub it upon the other
both sideways and lengthways. Suppose that on being separated and
examined the bearing marks, shown as at A A and B B, Fig. 2446, on one
plate, and at C C and D D, Fig. 2447, on the other, and as those at A A
and B B are the narrowest, or in other words extend the least distance
across the plate, it is proof that this plate is more concave than the
other plate is convex, and therefore needs the most correction. This is
plain because whatever part of a plate touches another, will, if the two
are merely pressed together, only leave a bearing mark equal in area to
itself, while this area will obviously be increased in proportion as one
plate is moved about upon the other.
[Illustration: Fig. 2448.]
When the object is to merely produce a flat surface, independent of the
thickness or parallelism of the plate, it is not always necessary to
file or scrape the whole of the area showing bearing marks. Suppose, for
example, that the marks appear as in Fig. 2448, and as the bearing marks
at A A show that edge of the plate to be straight already, all that is
necessary is to ease the surface at B in order to let that side of the
plate come up.
When we have fitted two of the three plates together we must accept one
of them as a true one and (calling it No. 1) fit Nos. 3 and also 2 to
it, and then try Nos. 2 and 3 together. If these require correcting the
amount of correction must be made equal on each, and when this is done
we must accept one of these two (say No. 3) as the standard, fit No. 1
to it, so that Nos. 1 and 2 both having been fitted to No. 3 may be
tried together and both corrected equally; nor will the surfaces of any
of them be true until all three will interchange in this manner and show
a perfect contact.
It is to be noted, however, that in this process we have not altogether
eliminated the error due to the deflection of each plate. Suppose, for
example, a plate to be resting on its feet and its middle will sag or
deflect to some extent (very minute though it may be in a small plate),
and when we place another plate upon it the latter will also sag or
deflect if its points of contact are far apart, and in any event the
truing is performed by the bearing-marks, which the operator knows show
the darkest and the brightest where the contact is greatest; hence by
the time the contact marks show equally strong all over, the top plate
will have been fitted to suit the deflection of the lower one. Since,
however, the nearer the points of contact (between the plates) are
together the less the degree of deflection, it is better in trying them
to place the test plate on the top of the one being operated on. If the
plates are long ones it will not answer to have more than three points
of rest for the lower plate, unless the foundation on which the plate
rests is made so true that each resting point of the plate will bear
with equal pressure on the foundation plate or stone.
To eliminate as far as possible the deflection, the three plates may be
got up by the process described, and then finished by trying them when
resting on their edges (the trued surfaces standing vertical),
interchanging the three plates as before.
In this case the surface will be true when standing vertical as
finished, but there will still be some untruth from deflection when the
plates are rested on their feet, though it will be less in amount than
if the plates were finished on their feet as first described.
In finishing surface plates with a hand scraper, we have a surface that
bears in fine spots only, these spots being the tops only of the scraper
marks. Now the depth of the scraper marks are unequal, because
immediately after the scraper is sharpened it cuts the easiest and the
deepest, the scraper cutting less deep as its edge dulls. The operator
regulates this to some extent by applying a greater pressure to the
scraper as it gets dull, but from differences in the texture of the
metal and from other causes it is impracticable to make the scraper cut
equally deep at each stroke, as a result the tops of the scraper marks,
which are the points of contact of the plates, wear away quickest, and
the plate soon loses, to some extent, its truth.
Again, work that is so small as to cover part of the plate surface only,
wears the part of the plate to which it is applied, and although the
careful workman usually applies small work at and near the outside edges
of the plate only, still these are all elements tending to produce
increased local wear and to throw the plate out of true.
To obviate this difficulty the surface should be got up to bear all
over, thus greatly increasing its bearing area and proportionately
decreasing its wear. To produce such a surface the following plan was
adopted by the author in 1876.
The filing process was continued with fine Groubet files, and testing
the plates, rubbing them together sufficiently to mark them without the
use of oil. Very short file strokes must be employed, and great care
taken to apply the file to the exact necessary spots and places.
Then instead of using the scraper, No. 0 French emery paper was used,
wrapped over the end of a flat file. The plates being interchanged and
trued with No. 0, No. 00 was used, and the testing and interchanging
repeated. These grades of emery paper were then wrapped or folded over
the curved end of a piece of wood, the plates interchanged and rubbed
together as before, and the emery paper used as described for the
scraper. Subsequently Nos. 000 and 0000 French emery paper were
similarly applied until the plates were finished. Much assistance to
this method may be rendered by taking a piece of Water of Ayr stone, and
truing its surfaces by rubbing them on the plates after the fine filing
and before the emery papering. Then while applying the finer grades of
emery paper the stone may be rubbed (with oil or water) in various
directions over the surface. This has the effect of wearing off the very
fine protuberances due to the emery paper cutting the metal most around
its pores, and furthermore it causes the marks made in testing to show
more plainly.
In skillful hands this process very far surpasses, both in the
superiority of its results and in rapidity of execution, the scraping
process, leaving a brilliant polished surface, so smooth that it feels
as soft as satin, and the contact becomes so complete that no bearing
marks can be distinguished.
In this process great care must be taken in cleaning the surfaces before
applying them together, as the finest particle of dust will cut
scratches, which though imperceptible on scraped surfaces, appear very
coarse and deep on these smooth ones.
The amount of metal taken off by the finer grades of emery paper is so
small as to be scarcely appreciable, save that it slightly discolors the
emery paper.
The finest test for plates finished in this way is to rest the lower one
quite level, clean it with alcohol, wipe it clean with old linen rag and
finally with the palm of the hand, which if quite dry is more effective
than anything else. The eye should carefully sight the plate surface
with the light reflecting on that surface, when particles too fine to be
felt may be observed and wiped off with the hand. In dry weather it is a
difficult matter to clean the plates perfectly, as while one is being
cleaned the fine particles of matter floating in the air rest upon the
other; but in rainy weather the cleaning is much easier.
The plates being cleaned one must be lowered vertically on the other
where it will float, there being a film of air between the two which it
is almost impossible to exclude by pressure even though the plates be
moved while pressed together.
If under these conditions the surfaces are not true and the top plate be
set in motion in various directions, by a light finger touch it will
swing round, the parts of the surface most in contact being the centre
of motion. Suppose then the top plate to swing from one end it should be
turned end for end on the bottom plate, and if the location of the
centre of motion is still at the same end of the top plate, that plate
is high there, while if the centre of motion in both cases is at the
same end of the bottom plate it is the one that contains the error.
If the top plate swings upon its own centre of motion it must be moved
farther off the bottom one, first on one side and then on the other, to
discover if it or the bottom plate is in error; while if the top plate
swings first from one end and then from the other, one or both of the
plates are hollow and the top one must again be moved farther off the
lower one, and the test by motion continued. The error discoverable in
this way is very much finer than can be discovered by the marks of
contact, since a plate showing quite even contact when quite dry and
clean, and tested as lightly and carefully as may be will show error by
this motion test. The error being so small in amount that it may be
corrected by rubbing the plate with rag and oil, applied under hand
pressure to the plate.
To cause the plates to bind together so that rubbing one on the other
will leave contact marks, the top plate must be placed about an inch
over the corner of the bottom one, pressed closely to it and forced
laterally over it. A pair of plates of the Whitworth pattern (such as
shown in Fig. 2449) placed by the author in the Centennial Exhibition,
required, when put together dry as above, 341-1/2 lbs to _slide_ the top
one over the other, which was due to the friction caused between the
surfaces by the atmospheric pressure acting on the back surface of the
plate, the latter having a superficial area of 12 by 8 inches.
Here it may be added that a plate of the same dimensions, and having its
surface finished simply by filing with a dead smooth file, which plate
was made for exhibition at a lecture on hand work, delivered before the
Spring Garden Institute of Philadelphia, required a force of 22 lbs. to
slide on the one on which it rested.
[Illustration: Fig. 2449.]
If two plates finished by the above method be placed together by sliding
one upon the other it will be found that with the hands applied as in
Fig. 2449, they can be separated or pulled apart with less force than it
requires to slide one upon the other, because the plates bend and unlap,
as would be the case if two sheets of paper were wetted and placed
together and then taken apart by pulling two edges in opposite
directions. But if the power to pull the plates apart be applied at the
middle of the plate it will require a much greater force to separate
them, although how much is problematical, no experiments having been
made upon the subject. Furthermore the friction between two such plates
will be greater if the surfaces be lubricated than if quite dry.
Thus, with the surfaces cleaned by alcohol, the top plate will move
comparatively easily, but if the surfaces be slightly oiled and then
wiped apparently quite clean with old dry rags, the friction will be a
maximum. If then a piece of rag, say of an area of an inch, have one
drop of oil upon it and be then applied to the surfaces of two plates
after they have been cleaned with alcohol, the friction will still be
about 3 lbs. per inch of area of one plate. With the surfaces well
lubricated it will still require more power to slide one plate upon the
other than would be the case were both plates quite dry.
The reason of this is that when quite dry it is impracticable to exclude
the air from between the surfaces, whereas with the lubrication the air
is more perfectly excluded and the atmospheric pressure forces the
plates together.
CHAPTER XXVIII.--ERECTING.
ERECTING.--The term erecting is applied in large work to the operations
involved in fitting the parts to their places on the engine or machine,
as well as to placing them upon their foundations and putting them
together ready to run.
In vice work or fitting, the various parts are put together ready to be
erected, each part being complete in itself, but not adjusted with
relation to the others. Thus, while a link motion may be complete in
itself, the length of its eccentric rods will usually require correcting
when placed upon the engine. Furthermore the position of the eccentric
is to be adjusted.
The boiler fittings may be complete in themselves, but will still
require to be fitted or erected upon or to their places.
Erecting requires the greatest of skill, care, and judgment, in order
that the work may be put together properly aligned and any defects of
construction corrected in the finished machine.
In erecting a machine, as in building a house--or, indeed, as in
everything that man constructs--the work must be begun at the
foundation.
In a machine in which the working parts are carried and contained upon
framework, such framework becomes the foundation so far as the erector
is concerned.
In a stationary steam engine the cylinder and bed plate form the
erector's foundation while the engine is in the shop, the mason's
foundation being an after consideration.
In a locomotive the boiler is the foundation to which all the other
parts are either directly or indirectly affixed.
The erector uses all the measuring tools used by the fitter or vice
hand, and in addition many others, as stretched lines, the spirit-level
and plumb-level. Either of these tools forms the readiest means of
testing whether surfaces that are widely removed and in different
positions about a machine are parallel one to the other, it being
evident that all surfaces standing vertical will be parallel, or all
those standing horizontal will also be parallel, one to the other.
Spirit-levels are often made of wood, which is very objectionable for
the erector's use, because the lower or testing surface is apt to catch
and hold particles of metal, and furthermore it is very susceptible to
abrasion, and wears rapidly. It is preferable, therefore, that it be of
iron or steel. The test of a spirit-level is its sensitiveness, and it
is found in a properly constructed one that the bubble will move to a
perceptible extent if a piece of gold leaf be inserted under one end. In
a spirit-level which came into the hands of the author of this work he
found the warmth of the finger when placed on its top sufficient to
cause the bubble to move nearly the full length of its tube, the body of
the level being a block of iron 1-1/4 inches square and 9 inches long.
The movement of the bulb was caused by the heat of the finger expanding
the top of the spirit-level and causing it to bend. To test the truth of
a spirit-level, it should be placed upon a true surface, as a surface
plate, and if the bubble comes to rest at the same spot in the length of
the spirit tube when the level is tried turned end for end, the level is
true. The test should be made several times.
[Illustration: Fig. 2450.]
The plumb-rule, though less used by machinists than formerly, is better
for machinists' use than the ordinary wooden-bodied spirit-level, since
it is more delicate if properly constructed. It should be formed as in
Fig. 2450, the sides A A and B B being straight and parallel one to the
other; C and D are two plugs of soft yellow brass let in so as to keep
the line _l_ _l_ clear of the face of the level, so that there shall be
no friction between them. At N are notches to secure the line, which
should be as fine and as closely spun as possible.
[Illustration: Fig. 2451.]
The plumb-level, Fig. 2451, is also preferable to the ordinary
spirit-level; its edges A, B must be straight and at a right angle one
to the other, C and D representing brass plugs as before. The edge A of
the rule or of the level should be laid upon a surface plate, and a fine
line drawn on the face of these plugs with a scribing block, the
coincidence of the line _l_ with these marked lines testing the truth of
the work.
FITTING OR MAKING JOINTS.--The best form of joint to withstand pressure
is the ground joint, and next to this, but more expensive, is the
scraped joint. The difference between the two is as follows:--
For a ground joint the fitting with files or scrapers is only carried
far enough to bring the fit sufficiently near that it may be finished by
grinding the surfaces by rotating one upon the other with oil and emery
interposed between them.
To grind a joint it is obvious that all the bolts or studs must be
removed.
In a scraped joint the scraping is carried to such a point of
correctness that the fit will be tight without grinding.
Joints in new work are easily ground, because the bolts or studs being
new have not become rusted in their places and may therefore be readily
removed; furthermore the joint may be ground before the studs are
inserted. But in the case of old joints the studs may have become so
rusted to their places as to render them liable to break off in the
effort to extract them, and in such case it is better in most cases to
make a scraped joint, which may be done with the studs left standing in
their places.
To make a ground joint, as say a cylinder cover joint, proceed as
follows:--
Put a thin coat of red marking upon the joint face of the cover, and
after it is coated lightly and smoothly all over, the hand should be
passed over the whole surface marked, because any grit left on the
surface will cut the faces of the joint when they are rubbed together to
fit them, and there is no wiping material that will so effectually clean
dust from the surface as the hand will; and furthermore, the sense of
touch will instantly detect any grit present. The cover may now be put
into its place on the cylinder and rotated back and forth a turn or so
to insure that it is properly seated; then we may strike it a light blow
in different places with a piece of wood or the end of the handle of
the chipping hammer; and if the cover does not fit pretty closely to its
seat, a sharp metallic sound will be distinctly heard when the blow is
struck over the parts of the face that are much out of true. Hence, by
striking the blows all around the flange, we can easily find not only
the high and low spots, but can determine, after a little practice, by
the degree of the sound, how much the faces are out of true. We next rub
the cover back and forth on its seat, so that the marking on the cover
will mark the high spots on the cylinder face. If, however, we make the
forward reciprocating movement of the cover a longer one than the
backward, we shall give to it a gradually rotary as well as a
reciprocating movement, and this will tell us if the face of the cover
is true or not, for if the marking is removed from the face of the cover
in two diametrically opposite places only, it shows that the cover
itself is not true; and if the cylinder face also marks on two
diametrically opposite places only, it is proof that both the faces are
a good deal out of true: but there is no knowing which one is the most
out, and so we must file off each an equal amount. If either face marks
in more than two places it is evidence that it is pretty nearly true,
and it follows that that face does not need much filing. Here it becomes
necessary to state why the movement of the cover must, when being tried
to its place, be back and forth, as well as rotated by the movement
already explained. If we revolve a radial surface of metal upon a
similar surface they are extremely liable to cut or abrade each other,
and the presence of the least grit will inevitably cause them to cut;
and if cutting once begins, the metal gathers upon the cutting part,
increasing its size so that the groove cut will get deeper until a
complete revolution has been made, and this rule applies to all
revolving surfaces, but more particularly to radial or conical ones.
By making the movement a partly reciprocating one we destroy this
tendency, and either imbed the grit into the iron or else work it out.
To proceed, however. If during our testing the blows induced a secondary
and metallic sound as above described, we take a rough file and ease the
high spots on both the cover and the cylinder face, filing a good deal
off the face that shows diametrically opposite bearing spots only, and
but very little off the face that shows three or more bearing spots. In
this latter case, indeed, it is better to use a second-cut than a rough
file. We next wipe both faces quite clean, apply the marking to the
cover as before, and try it to its seat again; rubbing it in the same
manner to its seat and testing it for the metallic sound as in the first
case. So soon as this sound ceases we may take a second-cut file and fit
the faces until they bear in at least four different places, when a
smooth file should be used and the fitting and trying continued, until a
very light coat of the red marking will show both the cover and the
cylinder face to mark in spots not more than an inch apart; and we may
then take a flat scraper, ease away the high spots, pressing the scraper
firmly to its work and making it cut fine scrapings, using the scraper
in strokes of about 1/2 inch for a large face and 1/4 inch for a small
one. When the two faces show about an even contact all over, the
grinding may be performed as follows:--
The two faces must be wiped quite clean, and then with an oil-can we can
run a line of oil around both the cylinder and cover faces, and then
with the fingers sprinkle on them some dry grain emery, of a grade of
about 50 for a cylinder whose diameter is, say, 14 inches or over, and
of a grade of about 60 to 65 for smaller diameters; if, however, only
coarser grades of emery are at hand it may be ground finer by abrasion
on an iron block, using a hammer face to grind it with. The emery and
oil being applied, we place the cover in its place upon the cylinder,
and give to it the reciprocative rotatory movement already described,
continuing the movement until the cover moves so smoothly and
noiselessly that it is evident that the emery has done its duty. We then
take the cover off and examine the faces.
If there are prominently bright spots upon either face, denoting that
the emery has not operated upon them, it will pay to take the scraper
again and ease away the dullest and most frosted-looking spots, which
denote that they have suffered most during the grinding operation. The
difference between the spots that have been the most and those the least
affected by the grinding will be very plainly visible if the faces are
wiped clean. We must continue the grinding operation with this grade of
emery until the marks show the grinding to have been performed pretty
evenly all over the faces, and we then apply a coating of oil and emery,
as in the previous operations, the latter being in this case of a grade
of about 70, moving the cover as before until it revolves so smoothly
and noiselessly as to indicate that the emery is no longer doing any
duty. Having continued this process, applying fresh emery and oil until
the face appears true, we may perform the finishing and testing process,
which is of the utmost importance, since it will detect the faintest
possible defect in the job. Wiping the faces quite clean, we put the
cover in place upon the cylinder again, and move it as before back and
forth, and yet slowly advancing; but it must be borne in mind that if
the cover makes the least jarring noise during the operation we must at
once remove it and wipe it clean again, or the faces will abrade and
become destroyed. There is no danger of this, however, if the cover be
at once removed when the jarring sound is heard. If it be not heard, we
continue the operation until the cover has made four or five
revolutions, and then remove it, and we shall find that the emery and
oil, which had impregnated the surfaces, have worked out. We again wipe
the faces clean and put them together and rub one upon the other as
before, bearing in mind that if the faces cling much one to the other,
we must wipe them clean again. Usually the finishing process requires
performing about three times, and then the faces will have become as
bright and clear as a mirror, magnifying the slightest defect in the
joint. Joints made in this way will stand any pressure without leaking
(unless the pressure be so great as to spring the metal of the cover).
It is well, however, when making the joint, to put a little oil or pure
tallow on it, and it is from this that it is called in England a grease
joint, while in the United States it is termed the ground joint. It is
common, however, in England to finish the whole joint by scraping; but
this is a much more tedious job, and not so good a one, after all. Here
it becomes necessary to remark, that in order to be able to handle the
cover readily, it is best to bolt to it a wooden lever overhanging both
sides of the cover, and to serve as a handle in moving it. And during
the grinding we may place a weight on the cover, which will greatly
expedite the process. It would appear that this is a long job, but such
is not the case; indeed, a 16-inch cylinder face and cover 1/32 inch out
of true one with the other can be got up in half an hour.
It is to be observed, however, that the cylinder cover that contains the
stuffing box for the piston rod often carries one end of the guide bars,
and in any event carries the gland whose bore requires to stand in line
with the cylinder bore. It must be remembered that if more is filed off
the top than off the bottom of the face, or _vice versâ_, the gland bore
may be thrown out of parallel with the cylinder bore, and the guide bar
seatings will be thrown out of parallel in the same direction.
To facilitate the making of ground and scraped joints it is preferable
that the surface of the joint, both on the cylinder and the cover,
project from the rest of the flange, from the bolt holes to the bore in
the one case, and from the bolt holes to the body in the cover in the
other, so that the bearing surface of the joint shall extend from the
inside edge of the bolt holes to the cylinder bore only. This provides
ample surface to make a joint, while reducing the surface to be operated
upon.
TO MAKE A SCRAPED JOINT.--Let us now suppose that the studs are in their
places, and it is decided, for fear of breaking them in taking them out,
to make a scraped joint, and the process is as follows:--
The testing and marking of the high spots or places must be made by
giving to one of the surfaces a light coat of red marking and then
bolting up the cover moderately tight, screwing up the nuts at first
until they just grip the work all around, and not letting one part of
the cover face bear at any time with greater pressure against the
cylinder face than there is on the diametrically opposite side of the
cover, for the side under most pressure will receive the marking most
readily. Especially is this the case when the two faces first meet,
because even a low part of the face will show most contact under such
circumstances, and then easing such marks away will make the cover a
worse fit than it was before. When the cover is bolted home, the marking
on the cylinder face may be made to transfer itself on to the high spots
of the cylinder cover face more plainly if a piece of wood be placed on
the cover and struck lightly with a hammer, moving the wood around and
between the studs. If the wood be struck heavily it will cause an almost
endless and assuredly a faulty job, because the force of the blow will
spring that part of the cover to its seat on the cylinder face, whether
it fits in that particular spot to its seat or not, and hence the filing
or scraping may be done in places where it is not required, because the
marking misleads. If the bolt holes are very close together, as in
English practice, lightly striking the cover will prove an assistance;
but where they are several inches apart, as in American practice, it is
better to omit it, for the bedding marks will show plainly and properly
if the marking be evenly distributed by the hand over the cylinder face,
and the cover is bolted at each trial tightly to its seat, providing of
course that the red marking is free from grit.
In a job of this kind it is difficult to know, when a leak occurs,
whether the defect is in the cylinder face or the cover, and it is very
desirable to perform the operation with a view to correct the defect
rather than bed one face to the incorrectness of the other.
If then the stud holes are equidistant apart and concentric (so as to
permit it), the cover may be tried on in one or two positions, and, if
the bearing marks occur on the cover at each trial in the same places it
is the cover that is out; or if this occurs on the cylinder face, it is
that face which is out. Since the studs are in their places the cylinder
face may be best operated on by a scraper, while for the first part of
the operation on the cylinder cover a file may be used. The corner at
the junction of the cylindrical part of the cover (where it fits into
the cylinder bore) should be scraped well clear, or it will be apt to
bind on the edge of the cylinder bore and prevent the cover from
screwing fairly home to the cylinder face. The joint should be made to
bed well inside of the bolt holes, and coated with oil or grease when
finally put together.
JOINTS FOR ROUGH OR UNTRUE SURFACES.--The most permanent form of joint
for a rough or untrue surface is, for steam pressure, a gauze, and for
water pressure, a pasteboard, or a duck or canvas joint.
A gauze joint is composed of copper wire gauze, having square meshes of
about 1/32 inch square; this gauze is cut out to fit over the joint
surfaces, a single, double, or treble thickness being used according to
the unevenness of the surfaces. A coating of red-lead putty is first
spread over the joint with a piece of smooth surfaced metal; the wire
gauze is then put on, and over it another coating of red lead; the cover
is then put on, and the nuts screwed lightly home so as to bring the
cover to bear against the red lead. Then any nut may be given a quarter
or a half-turn, and the diametrically opposite one also given a
half-turn, this process being continued until all the nuts have been
screwed home a half-turn, when the process may be continued until the
nuts are screwed firmly home. This is necessary, because if the nuts on
one side are screwed home in advance of those on the other, the red lead
on that side may be squeezed out too much and the joint will leak. In
joints of this class the surfaces being rough it is not unusual to cut
out the gauze wire as follows: Lay the sheet of gauze over the joint and
cut it to the size by lightly hammering it over the sharp edges of the
joint, which will cause the sharp edges to cut the copper wire. To cut
out the holes place the ball piece of a hand hammer on the wire and over
a hole and strike the hammer face several light blows, and the corners
of the hole will cut the wire through.
The gauze joint will answer equally well for hot water as for steam
joints, provided that it be given time to dry and become hard. If the
joint can have a week in which to dry the red-lead putty may have about
one-sixth of its bulk of white lead mixed with it, being made to a
consistency of soft dough so that it will spread easily; and the amount
being sufficient to fairly cover the gauze and no more, the soundness of
the joint may be known by the lead squeezing out all around the joint
edge as the bolts are screwed home. If the joint is to be used in a day
or so after being made, the white lead should be omitted. In either case
the lead should be mixed stiffly at first; the best lead should be used
and it should be well hammered on an iron block, after which it may be
thinned with boiled oil, or with a little varnish, which will cause it
to harden more quickly.
For water joints requiring to stand high pressure, and to be used as
soon as made, a paper, pasteboard, or a duck or canvas joint are best.
The joint is made by using, in place of the gauze wire, one or two
thicknesses of the pasteboard, duck, or canvas, cut out to the size of
the flange, and with the necessary holes to receive the standing bolts
and leave the bore of the pipe clear. If the flange of the joint is of
copper, brass, or wrought iron, or, if of cast iron, is of sufficient
strength to permit it, one disk may be made the full size of the flange,
and a second may be made to have an external diameter sufficiently large
to fit snugly inside of the bolt holes, which will form sufficient
thicknesses if the flange is a fair fit to its seat; if it is not,
however, three, or even four, thicknesses may be used, in which case at
least one of them should fit inside the diameter of the flange across
the bolt holes, as described. The disks being prepared, we spread on the
first one a thin coating of red-lead putty, and then lay another canvas
disk on, again adding the putty until the whole is completed. We then
spread a thin layer of the putty around the hole of the seat and that of
the flange, place the disk in position and screw the joint up,
tightening down the nuts until they bring the flange to an equal seating
all around and not sooner on one side than on another, for in that case
the red-lead putty will be squeezed unevenly, and too much on the side
screwed up to excess. The nuts should be screwed up very tight; the
joint wiped, the protruding canvas cut off, and the joint is complete.
For very rude and rough joints, whether used under pressure or not, we
may make, for either water or steam, a joint as follows: Taking four or
five strands of hemp, we saturate them with a coating of white lead
ground in oil, applying just sufficient to make the fibres of the hemp
cling well together. We then plait the strands and coat the whole rope
thus formed with red-lead putty, and place the strand around the hole of
the joint, taking care that the ends lap evenly, so that the joint shall
be of even thickness. It is better, however, to bend a piece of lead or
iron wire to suit the size and shape of the hole in the joint, and then
wind the hemp and red lead around the wire. And in cases where the
flanges of the joint are sufficiently strong to have no danger of their
breaking from the pressure due to screwing up the nuts, the piece of
lead wire, if given a neat butt joint or neatly lapped, may be employed
without any red-lead putty or hemp; this does not, however, make a good
permanent joint. In cases where a joint requires to be made thick to
accommodate the length of the pipe, pasteboard may be used in the place
of canvas, giving to it a thinly-spread coating of red-lead putty on
each side, and, if possible, leaving the pasteboard a trifle too thick
and springing open the flanges of the joint to get the pasteboard into
position without scraping off the red-lead putty.
Where it is required that a joint stand great heat or fire, asbestos
board, about 1/16 inch thick, makes a good and permanent joint. It is
coated with red lead mixed thinly with boiled oil, containing as much as
it will soak up, leaving a thin layer of the lead upon the surface of
the asbestos. The holes for the bolts to pass through in the duck,
canvas, pasteboard, or asbestos joint should be cut large enough to well
clear the bolts.
For cold water, where it is not subject to great variations of
temperature, common sheet lead makes a very good joint; but under
excessive changes of temperature the expansion of the pipes will soon
cause the sheet lead to squeeze out and the joint to leak.
Joints are frequently made with copper wire rings, made of a diameter to
pass around the hole of the joint and lie within the diameter of the
bolt holes, and brazed together at the ends; but if the joint be
rectangular instead of circular the wire must either lie in a recess, or
else a shoulder must be left for the wire to abut against, which will
prevent its blowing or becoming forced out by the pressure.
In some practice softened sheet copper about 1/32 inch thick is used to
make joints on surfaces that have been planed. Joints of this kind are
used for locomotive steam chests.
Rubber joints are used to make steam, water, and air-tight joints, and
are usually made from what is known as combination rubber--that is,
sheet rubber having a linen or other web running through it; with one
such web it is called single, and with two webs two-ply, and so on.
There is in many cases, however, an objection to this form of joint, in
that it compresses; and hence in the case of the steam chest, for
example, it affects the distance of the slide-spindle hole in the chest
from the seat, and throws it somewhat out of line with the eccentric. In
long eccentric rods the variation is of course minute; but still it
exists, and must exist, since it is impossible to tell exactly how much
the rubber will compress in making the joint. Furthermore, if it is
required to break such a joint, the rubber will very often cling so
tenaciously to the seat in one place and to the chest in the other, that
it will tear asunder in breaking the joint. To obviate this as much as
possible, however, we may chalk the rubber on one face and slightly oil
it on the other, so that the oil will aid the rubber in clinging to one
face, while the chalk will assist it in separating from the other face
of the joint.
Rubber joints slowly compress after being under pressure a day or so,
and also if subjected to heat; hence they should have their bolts
screwed up after becoming heated, or after having stood some time. It is
advisable also that the rubber be as thin as the truth of the surfaces
will admit. If it is necessary to use more than one thickness of rubber,
the thickness may be made up of rings, whose diameter will just pass
within the bolt holes.
The holes in a rubber gasket should be made larger than the bolt holes,
so that there shall be no danger of the bolt, when being inserted,
catching the gasket.
If the flanges should not come fair, and it is determined not to set
them fair, the rubber should be as thick as the widest part of the
opening between them, and shaved off to suit the thin side of the joint,
and in this case the bolts must be tightened very uniformly and
gradually around the joint to secure a tight one. If there is room to
shave the gasket to the amount of taper, and use in addition a ring
around the bolt holes, it will make a safer job.
When the gasket requires to be split to pass it around or over a rod, it
should be cut through to the canvas on one side, and a short distance
off cut through to the canvas on the other side; the rubber may then be
stripped carefully back from the canvas and the latter cut through and
passed over the rod, when the rubber may be put back and sewed to the
canvas again.
Sheet rubber with a gauze wire insertion instead of canvas makes an
excellent joint.
[Illustration: Fig. 2452.]
In Fig. 2452 is shown a method of making a steam-tight joint largely
employed in England, upon the steam chest joint where the cylinders of
crank shaft (inside cylinder) engines are bolted together. A is the
flange of one cylinder, which is bolted to the other by the bolt B. C is
a strip of copper let into a dovetail groove cut one half in one
cylinder, and the other half in the other. After the bolts B are all
firmly screwed home, hammer blows are delivered upon the top of the
copper strip as denoted by the arrow E, expanding the copper so that it
completely and closely fills the dovetail groove, and makes a
steam-tight groove.
In riveting the copper it is necessary to hammer it evenly all along
lightly, and only sufficiently to make it closely fill the groove,
otherwise it will spring the joint open, and cause it to leak,
notwithstanding the bolts B, which will give under the extreme strain.
Temporary joints are sometimes made by bending a piece of lead wire into
a ring or frame, of such a size as to well clear the inside of the bolt
holes. The ends are neatly joined, and the lead wire compressing and
accommodating itself to the inequalities of the surfaces forms a joint.
[Illustration: Fig. 2453.]
[Illustration: Fig. 2454.]
JOINTS FOR BOILER FITTINGS.--Let it be assumed that the casting shown in
Figs. 2453 and 2454 requires to be fitted to a boiler, both being new.
In this case, the holes for the studs or bolts should first be drilled
in the flange of the casting, which will reduce its weight and render it
easier to handle. The casting should then be held against the boiler in
its proper position and location; and, with a fork scriber whose width
of points is equal to the widest space between the face of the casting
flange and the boiler, pass the fork scriber around the fitting or
casting with one point against the boiler shell and the other pressed
against the edge of the casting, the result being to mark around the
flange of the latter a line exactly following the surface or contour of
the boiler, and at a distance from the boiler the nearest that will
suffice to properly bed the casting to the boiler surface, or, in other
words, the line that will exactly mark the amount of metal requiring to
be cut off the flange face to make it bed all over; and that face may,
therefore, be cut down to the line. In chipping and filing it, however,
the straight-edge may be used to advantage as follows:--
[Illustration: Fig. 2455.]
Suppose the casting flange to be gripped in the vice facing the
operator, as in Fig. 2455, and that L L represents the scribed line:
then the cape chisel cuts may be carried clear across the flange, coming
exactly down to the line on each side of the flange, while a
straight-edge S may be used as shown to show when the cut is carried
across level. Then, when the intermediate spaces are cut out with the
flat chisel the surface will be of correct shape, and the surface may be
rough filed. The casting should be cut clear down to the lines, and if
the job has been properly set, marked and faced, no further trying will
be necessary previous to marking the bolt or stud holes in the boiler.
It is well, however, if the operator is inexperienced in this kind of
work, to again set the casting in its proper position to correct the
fit. But, with proper care, all the holes in the boiler may be marked
without any second fitting of the flange, since the operation properly
performed is bound to give correct results. In doing a job of this kind
it must be borne in mind that it is very easy to consume more time in
trying and altering the job than is required under proper conditions to
do the entire job; hence, in setting the casting, preparatory to marking
it with the fork scriber, nothing is near enough that does not carry
with it a conviction of perfect reliability; and if any doubt exists it
is better to go through the process again. If the casting flange varies
much in shape from its seat, and rocks or is unsteady, wooden wedges may
be placed beneath it, or a few pellets of stiffly mixed red lead may be
placed on the boiler where there is most room between it and the
casting, the boiler surface being coated or painted with red marking, so
that the pellets shall adhere to it and not to the flange face. If the
casting is too heavy to be steadied by hand, one hole may be drilled in
the boiler and a temporary bolt inserted to hold the casting while
setting it in position, and marking with the fork scriber.
When the flange is approaching a fit, it must be placed in position on
the boiler and the stud holes marked on the boiler with an ordinary
scriber, its point being pressed against the boiler while it is pressed
against the side of the hole in the casting flange and traversed around
it, so as to scribe on the boiler surface circles corresponding to the
holes in the flange. From the centres of these circles others of the
proper size of the tapping holes may be struck and the tapping holes may
then be drilled, and the studs put in. The remainder of the fitting
operation consists in applying red marking on the boiler surface,
bolting the casting to its place and filing the high spots. The marking
is made to show plainly upon the flange by light hammer blows with a
piece of wood interposed between the hammer and the flange face to
prevent piercing the latter. These blows, however, should be lightly
delivered, or they will cause the marking to be deceptive.
[Illustration: Fig. 2456.]
The fit of the flange to the boiler, however, should vary according to
the kind of bolt used to hold the fitting to the boiler. If stud bolts
are used they are supposed to screw into the boiler steam-tight, hence
the flange may be fitted so that it has the closest contact with an
annular ring extending from the outside of the bolt holes to the central
hole of the flange, as shown in Fig. 2456, in which the area within the
dotted circle C encloses the area to be most closely bedded. This is a
highly important consideration in flange joints of every description,
for, if a joint is made there, that is all that is necessary, and the
fit outside of the bolt holes--that is to say from the bolt holes to the
perimeter of the flange--has nothing to do with making the joint, unless
the studs or bolts leak, and in that case the leak will find egress
beneath the nut, unless grummets are used. A grummet is a washer made of
twisted hemp, cotton, or other material, and coated with red-lead putty,
and is placed beneath the heads of bolts, or under washers placed
beneath nuts to stop leaks. It is not necessary to ease the flange from
the bolt holes outward much, but to merely make the flange, or fitting,
bed clearly and distinctly the most around the main hole, and outwards
to the inside of the bolt holes; for, if there was given too much
clearance, the flange would bend from the pressure of the nuts, and
would in consequence spring if made of brass, or perhaps break if made
of cast iron.
To make the joint, gauze wire, pasteboard, or asbestos board may be
used, or if the joint is to have ample time to set, a red-lead joint
without the gauze may be used; but in this case it is an advantage to
cut up into pieces about 3/8 inch long, and thoroughly shred some hemp,
and well mix it in the lead, well beating the same with a hammer.
To preserve red-lead putty from becoming hard and dry, as it will do if
exposed to the air, it should be kept covered with water.
In some cases joints of flanges to boilers are made by riveting the
flanges to the boiler and caulking or closing the edge of the flanges to
the boiler shell; but this possesses the disadvantage that the rivets
must be cut off to remove the fitting from the boiler when necessary,
and access to the interior of the boiler is necessary in order to attach
the fitting again by rivets.
[Illustration: Fig. 2457.]
Fig. 2457 (which is taken from _The American Machinist_), represents a
joint for boiler fittings, designed to facilitate the breaking and
re-making of the joint. C represents, say, a boiler plate, B a piece
having a ball joint seat in C ground steam tight, and A a flange, say,
for a feed pipe; the studs D thread permanently into C, and the joint is
bolted up by the stud nuts E. It is obvious that the ball joint between
B and C permits the flange A to set at an angle if necessary.
RUST JOINTS.--These are joints made by means of filling the space
between the flanges, or annular spaces, as the case may be, with
cast-iron turnings, and compacting them with a caulking tool. Any
interstices through which steam or water, &c., might leak become filled
by the subsequent rusting of the iron cuttings, the rust occupying
considerably more space than the iron from which it was formed.
[Illustration: Fig. 2458.]
Rust joints are employed upon very uneven surfaces, and for pipes for
mains to go under ground. In former times this class of joints was much
used in engine and boiler work, but of late years it has been to a great
extent abandoned. In Fig. 2458 is shown the method of construction for
a rust joint for what are known as spigot and socket joints for pipe
work. S is the spigot and P the socket. R R is a metal ring, bound over
with either dry hemp fibre or tarred twine or rope. The remainder of the
space between the pipes at A A being filled with a cement composed of
Sifted cast-iron borings 100 lbs.
Sal-ammoniac 1/2 lb.
Sulphur 1/2 lb.
but when required to set quickly, 1 lb. sal-ammoniac may be used. These
ingredients are thoroughly mixed with water immediately before being
used, and just covered with water when used intermittently. The cement
is put into the space A A, in quantities sufficient to fill up about 3/4
inch in length of the annular space A A, and then caulked by being
driven in with the tool shown in Fig. 2459. Cement is then again put in
and the caulking repeated, the process being continued until the whole
space is filled.
[Illustration: Fig. 2459.]
In some cases (as in gas mains) the space A A is filled with melted
lead, and when cold caulked with the tool described.
[Illustration: Fig. 2460.]
In Fig. 2460 is shown the method of making a rust flange joint; A A
being a ring covered with hemp twisted around it, the cast-iron cement
being caulked in as before.
The wire rings should be firmly gripped by the bolts to prevent them
from moving from the caulking blows, which should be at first delivered
lightly.
[Illustration: Fig. 2461.]
In some cases pipes are joined with rust joints, as in Fig. 2461 in
which A A is a sleeve, there being two rings of wire and hemp inserted
as shown.
When flanged joints are made with a scraper, or ground joint, or with
rubber, duck, or other similar material to make the joint, the length of
the pipe, from face to face of the joint, must be made accurate.
[Illustration: Fig. 2462.]
Fig. 2462 is a face, and Fig. 2463 (which are from _Mechanics_), a
sectional edge view of an expansion joint, being that used by the New
York Steam Supply Company for the steam pipes laid under the streets to
convey steam to buildings. The object is to provide a joint which shall
permit and accommodate the expansion and contraction of the pipe under
varying temperatures. P P are corrugated copper disks secured to the
faces of the pipe ends by flanges, as shown, and gripped at their edges
by the flanges of the cast-iron casing, and it is obvious that the ends
of the pipe may move longitudinally carrying the corrugated disks with
it. The cavity A is filled with steam, and to support the disks P
against the pressure segmental blocks B of cast iron are placed behind
them, the number of these blocks being as indicated by the dotted radial
lines in the figure. It may be added that this joint has been found to
answer its purpose to great perfection.
[Illustration: Fig. 2463.]
Pipe cutters, for cutting steam or gas pipe by hand, are usually
provided with either a rotary wheel which severs by rolling an
indentation, or else are provided with cutting tools. The rolling wheel
has the advantage that it makes no cuttings, cuts very readily and is
not apt to break; on the other hand it is apt to raise around the
severed end of the pipe a slight ridge, which with a worn cutter may be
sufficiently great as to require to be filed off before the threading
dies will grip the pipe. Cutting tools are apt to break and require
frequent grinding; hence, as a rule, the rolling wheel cutter is
generally preferred.
[Illustration: Fig. 2464.]
Fig. 2464 represents a cutter of this kind, the piece A carrying the
cutter B, which is operated in the stock C by means of the threaded
handle H.
[Illustration: Fig. 2465.]
Fig. 2465 represents a pipe cutter in which are a pair of anti-friction
rollers and a severing tool bevelled on one edge only so as to leave the
end of the pipe face cut square, and the piece cut off bevelled on its
face; or by turning the cutter round the reverse will be the case, the
piece cut off being flat on its end.
The action of this cutter is, as in the case of the wheel cutter, simply
that of a wedge, hence no cuttings are formed.
[Illustration: Fig. 2466.]
Fig. 2466 represents a pipe cutter in which a cutting tool is employed,
being fed to its cut by the handle which is threaded similar to the
handle shown in Fig. 2464. The end jaw is operated to suit different
diameters of pipe by means of the milled nut shown, which receives a
threaded stem on the adjustable jaw.
[Illustration: Fig. 2467.]
PIPE VICE.--The ordinary bench vice is sometimes provided with an
attachment to enable it to grip pipe at three points, and, therefore,
hold it sufficiently firmly without squeezing it oval, but it is
preferable to use a proper pipe vice, such as shown in Fig. 2467, which
consists of a base frame bolted to the work bench and receiving a
serrated die to grip the pipe. The upper die is carried to a frame
pivoted on both sides to the base, and is operated to grip or release
the pipes by means of the handled screw shown.
[Illustration: Fig. 2468.]
To change the dies one pivot is removed and the upper frame swung open,
as in Fig. 2468.
[Illustration: Fig. 2469.]
The proper shape for pipe tongs depends upon the number of sizes of pipe
the tongs are intended for, but in all cases the point at which the
gripping point should be is about as shown in Fig. 2469. This enables
the edge at A to enter the work and grip it. If this point of contact
were nearer to C it would be apt to slip upon the pipe, whereas, were it
farther towards B, it would present a less acute angle to the pipe,
which would be apt to jam in the tongs.
It is obvious that, if the tongs be moved in the direction of H, the
whole power applied to F acts to cause the edge at A to grip the pipe,
and that the length from A to G has an important bearing on the grip of
A to the pipe; because the nearer A is to G not only the greater the
leverage of the leg F, but also the less A, with a given amount of
movement of F on its pivot, endeavors to enter the pipe; hence the
movement of A in a direction to grip the pipe is less in proportion to
the movement of F, and has a corresponding increase of force. It follows
then that the nearer the grip of A is to C, the less, and the nearer the
grip to B the greater, its grip upon the pipe. But, by making the
length of A such as to grip the pipe in about the position shown in the
cut, there is latitude enough in the location at which it will grip the
pipe to permit of the tongs being used upon pipe of a somewhat greater
or less external diameter, increasing the availability of the tongs.
Furthermore, if A gripped the pipe at or too near to B, it would be apt
to indent it. The crown of the jaw D may be made to fit to the pipe or
to be clear of it; for thin pipe, as solid drawn brass pipe, it should
fit so that the pressure will not indent the pipe, but for strong iron
pipe it is better to let it clear, which will not only afford a firmer
grip, but will also better fit the tongs to take in different diameters
of pipe. In some cases, as in adjustable pipe tongs, the jaw surface D
is, for this purpose, considerably [V]-shaped, as will be seen
presently.
It is obvious that as A grips the pipe automatically, the tongs may be
moved through any portion of a rotation that the location may render
most desirable. Pipe tongs are designated for size by the diameter of
the pipe they are intended for; thus, a pair of inch tongs are suitable
for pipe an inch in diameter of bore, the handles or legs of the tongs
coming so close together that both can be readily grasped in one hand
applied at their extreme ends. If, however, the tongs be applied to pipe
of a larger diameter the legs will be wider apart, and one hand will be
required to be applied to each leg to force them together. A complete
set of pipe tongs, therefore, includes as many pairs as there are
diameters of pipe, unless adjustable tongs be used.
[Illustration: Fig. 2470.]
[Illustration: Fig. 2471.]
[Illustration: Fig. 2472.]
Adjustable tongs are made of various forms; thus a simple plan is shown
in Fig. 2470. The gripping surface of the jaw is shaped as at V, so as
to admit varying diameters of pipe, the smaller diameters passing
farther up the V, the distance of the end A of jaw, or leg F, being
regulated to grip the pipe in the proper place by operating the screw S,
which is tapped into the jaw F and pivoted in B, the slot C enabling F
to move along B. The capacity of tongs of this design is about three
diameters of pipe, as 1, 1-1/4, and 1-1/2 inches. There are various
other forms of adjustable pipe tongs, but most of them possess the
disadvantage that the adjustable jaw hangs loosely, involving some extra
trouble in placing them upon the pipe, because one hand must be employed
to guide the loose jaw and adjust its position on the pipe. Fig. 2471
represents tongs of this class, the gripping size being varied by moving
the jaw A upon B at the various notches. The end of B is serrated to
afford a firmer grip upon the pipe. Fig. 2472 represents another
adjustable pipe tongs, which is made in two parts, a straight lever A
and hooked lever B, the former passing through a slot in the latter. The
back of the straight lever is notched and a serrated fulcrum piece C is
pivoted in the slotted lever by a pin upon which the lever B receives
its support when the tongs are in operation. The fulcrum piece is
provided with a spring which retains the serrated edge in proper
position to engage the notches in the lever A. By means of the thumb
piece D, the piece C can be moved in either direction to increase or
diminish the gripping size of the tongs. When the tongs are open the
lever A can be moved within the slot and adjusted so that the tongs will
fit the pipe. The fulcrum piece C, being pivoted, allows the full length
of its serrated edge to come into contact with the corresponding portion
of the lever A, so that the parts always have a firm bearing and are
subjected to an equal wear.
A common form of pipe tongs of this class is shown in Fig. 2473, B being
pivoted to A by a pin, and changing to various holes in A to suit
different diameters of pipe.
ERECTING PIPE WORK.--In erecting pipe work care must be taken to have it
align as true as possible, as well as to have the joints tight enough to
stand the required pressure without leakage. If the elbows, tees, or
other fittings are not threaded true, a pipe whose thread is not true
with its axis may be selected or cut purposely to suit the error in the
fitting, so as not to leave an unsightly finish to the job.
[Illustration: Fig. 2471.]
[Illustration: Fig. 2474.]
Suppose, for example, that in Fig. 2474, _e_ is a pipe erected parallel
to the wall, but that the holes in its elbows are tapped at an acute
instead of at a right angle, then by cutting the thread on the end of
pipe _d_ untrue with its axis, its far end will rotate out of true as
denoted by the shaded and by the plain lines, and all that will be
necessary is to screw up the pipe sufficiently firm to make the joint,
but to leave it in the position shown in the plain lines.
If the pipe tightens sufficiently before it has reached that position it
may generally be eased by rotating it back and forth in the elbow with
the pipe tongs. If this does not suffice, the pipe must of course be
threaded sufficiently further along. To cut a pipe out of true to suit
an untrue elbow, a very good plan is to cut the end of the pipe at an
angle to its axis, which will cause the dies to cant over when starting
the thread, but little practice being required to educate the judgment
as to how much to do this to suit any given degree of error.
In erecting pipe it is best to begin at one end and screw each
successive piece firmly home to its place before attaching another, so
that the lengths of the pieces may be accurate and not vitiated by
screwing them up and causing them to enter farther into the fittings. If
it is probable that the piping may have to be taken down after erection,
it should be put up at first screwed together rather tighter than will
be necessary, as the thread fits become eased by being moved one within
the other. This is especially the case with brass fittings, upon which
it is best in cutting the lengths of pipe to have it of full length, as
the threads will conform to each other sufficiently to cause the pipe to
enter a thread or so farther if the pipe be rotated back and forth a few
times in the fitting.
The fit should in all cases be made by tightness of thread fit, and not
by the union or elbow face jambing against the end of the thread or the
pipe, as joints in which this is the case will usually leak if used
under pressure.
The thread of both the pipe and the fitting should be smeared with a
thick lead paint. If the pipe is to be used as soon as erected, plain
red lead and boiled oil should be used for the paint; but if it may
stand a few days it is better to mix white and red lead in about equal
quantities, as this, if given time to dry, makes a tighter job. The
quantity of this paint should not be more than will thinly cover the
threads, otherwise it will squeeze out when the pipes are screwed home,
and falling from the end of the pipe within the fitting be apt to be
carried by the steam or water to the valves, and getting between them
and their seats cause them to leak. The iron cuttings should be
carefully cleaned both from the pipe and the fitting for the same
reason.
In cases where the piping may require to be used under heavy pressure as
soon as erected, it is a good plan to use dry red lead in varnish,
thoroughly hammering it to mix it well, and thinning it after it has
been so hammered.
In case of emergency a loose pipe may be somewhat improved by wrapping
around its thread a piece of lamp wick saturated with this varnish lead,
beginning at the end of the pipe and wrapping the thread from end to
end.
It is preferable that the stem of the valve stand nearly horizontal, so
that any water of condensation may pass freely away with the steam and
not collect and lie in the pipe as it does when vertical. If it be quite
horizontal the water of condensation will drip through the stuffing box;
hence it is better that it stand 10 or 12 degrees from the horizontal.
It is better in all cases to purchase nipples than to make them by hand,
because when made in a machine the threads are more true to the axis
than those made by hand; especially is this the case in short nipples in
which there is not sufficient length to use the guide socket when
engaged in threading the nipple with the hand dies.
It is a very good plan in making such short nipples to cut them off the
end of a length of pipe that has been threaded by machine, and to screw
on the threaded end a coupling. Into this coupling a piece of pipe may
be threaded to afford a hold in the vice. If then the nipple is long
enough, a guide to suit the size of the nipple may be used in the
threading dies, or a guide socket to fit the diameter of the coupling
may be used.
A globe valve should be so placed on the pipe that the pressure will,
when the valve is closed, fall on the bottom face of the valve, so that
the steam may be shut off while the valve stem is being packed.
Cotton lamp wick plaited to fit the packing space, and well oiled, is as
good as anything to pack the stem with.
In taking old pipe down a refractory joint may be sometimes loosened by
striking it with a hammer while it is under full pipe tongs pressure; or
these means failing, the elbow or tee may be heated, which should be
done as quickly as possible, so that the fitting may be hotter than the
pipe. A very good method of doing this, where it is desired to save the
fitting, is to pour red-hot lead over the fitting.
If it is not important to save the fitting, it may be split by a flat
chisel, or by cutting a groove along it with a narrow cape chisel; or if
the pipe is free the elbow may be rested on an anvil and hammered around
its circumference, which will either free it or break it, if of cast
iron.
When pipes are to be taken down and re-erected elsewhere they should all
be marked to their fittings and places before being taken down, as this
will preserve their lengths as near as possible for re-erection. Black
japan is an excellent marking for this purpose because it dries quickly.
RE-FITTING THE LEAKY PLUGS AND BARRELS OF COCKS.--When a cock leaks, be
it large or small, it should be refitted as follows, which will take
less time than it would to ream or bore out the cock or to turn the
plug, unless the latter be very much worn indeed, while in either case
the plug will last much longer if refitted, as hereinafter directed,
because less metal will be taken off it in the re-fitting.
After removing the plug from the cock, remove the scale or dirt which
will sometimes be found on the larger end, and lightly draw-file, with a
smooth file, the plug all over from end to end. If there is a shoulder
worn by the cock at the large end of the plug, file the shoulder off
even and level. Then carefully clean out the inside of the cock, and
apply a very light coat of red marking to the plug, and putting it into
the cock press it firmly to its seat, moving it back and forth part of a
revolution; then, while it is firmly home to its seat, take hold of the
handle end of the plug, and pressing it back and forth at a right angle
to its length note if the front or back end moves in the cock; if it
moves at the front or large end, it shows that the plug is binding at
the small end, while if it moves at the back or small end, it
demonstrates that it binds at the front or large end. In either case the
amount of movement is a guide as to the quantity of metal to be taken
off the plug at the requisite end to make it fit the cock along the
whole length of its taper bore.
If the plug shows a good deal of movement when tested as above, it will
be economical to take it to a lathe, and, being careful to set the taper
as required, take a light cut over it. Supposing, however, there is no
lathe at hand, or that it is required to do the job by hand, which is,
in a majority of cases, the best method, the end of the cock bearing
against the plug must be smooth-filed, first moving the file round the
circumference, and then draw-filing; taking care to take most off at
that end of the plug, and less and less as the other end of the plug is
approached. The plug should then be tried in the cock again, according
to the instructions already given, and the filing and testing process
continued until the plug fits perfectly in the cock. In trying the plug
to the cock, it will not do to revolve the plug continuously in one
direction, for that would cut rings in both the cock and the plug, and
spoil the job; the proper plan is to move the plug back and forth at the
same time that it is being slowly revolved. As soon as the plug fits the
cock from end to end, we may test the cock to see if it is oval or out
of round. The manner of testing the cock is as follows:--
First give it a very light coat of red marking, just sufficient, in
fact, to well dull the surface, and then insert the plug, press it
firmly home, and revolve it as above directed, then remove the plug, and
where the plug has been bearing against the surface of the cock the
latter will appear bright. If, then, the bore of the cock appears to be
much oval, which will be the case if the amount of surface appearing
bright is small, and on opposite sides of the diameter of the bore,
those bright spots may be removed with a half-round scraper.
Having eased off the high spots as much as deemed sufficient, the cock
should be carefully cleaned out (for if any metal scrapings remain they
will cut grooves in the plug), and the red marking re-applied, after
which the plug may be again applied. If the plug has required much
scraping, it will pay to take a half-round smooth file that is well
rounding lengthwise of its half-round side, so that it will only bear
upon the particular teeth required to cut, and selecting the highest
spot on the file, by looking down its length, apply that spot to the
part of the bore of the cock that has been scraped, draw-filing it
sufficient to nearly efface the scraper marks. The process of scraping
and draw-filing should be continued until the cock shows that it bears
about evenly all over its bore, when both the plug and the cock will be
ready for grinding.
Here, however, it may be as well to remark that in the case of large
cocks we may save a little time and insure a good fit by pursuing the
following course, and for the given reasons. If a barrel bears all
around its water-way only for a distance equal to about 1/16th of the
circumference of the bore, and the plug is true, the cock will be tight,
the objection being that it has an insufficiency of wearing surface. It
will, however, in such case wear better as the wearing proceeds. Plug
and barrel being fitted as directed, we may take a smooth file and ease
away very lightly all parts of the barrel save and except to within,
say, 3/8 inch around the water or steam-way. The amount taken off must
be very small indeed, just sufficient, in fact to ease it from bearing
hard against the plug, and the result will be that the grinding will bed
the barrel all over to the plug, and insure that the metal around the
water or steam-way on the barrel shall be a good fit, and hence that the
cock be tight.
The best material to use for the grinding apparatus is the red burnt
sand from the core of a brass casting, which should be sifted through
fine gauze and riddled on the work from a box made of, say, a piece of
1-1/2 pipe 4 inches long, closed at one end and having fine gauze
instead of a lid.
A very good material, however, is Bath brick rubbed to a powder on a
piece of clean board. Neither emery nor ground glass is a good material,
because they cut too freely and coarsely, which is unnecessary if the
plug has been well fitted.
Both the barrel and the plug should be wiped clean and free from
filings, &c., before the sand is applied; the inside of the barrel
should be wetted in and the plug dipped in water, the sand being sifted
a light coat evenly over the barrel and the plug. The plug must then be
inserted in the barrel without being revolved at all till it is home to
its seat, when it should be pressed firmly home, and operated back and
forth while being slowly revolved. It should also be occasionally taken
a little way out from the barrel and immediately pressed back to its
seat and revolved as before, which will spread the sand evenly over the
surfaces and prevent it from cutting rings in either the barrel or the
plug. This process of grinding may be repeated, with fresh applications
of sand, several times, when the sand may be washed clean from the
barrel and the plug, both of them wiped comparatively dry and clean, and
the plug be re-inserted in the barrel, and revolved, as before, a few
revolutions; then take it out, wipe it dry, re-insert and revolve it
again, after which an examination of the barrel and plug will disclose
how closely they fit together, the parts that bind the hardest being of
the deepest colour. If, after the test made subsequent to the first
grinding operation, the plug does not show to be a good even fit, it
will pay to ease away the high parts with a smooth file, and repeat
afterwards the grinding and testing operation.
To finish the grinding, we proceed as follows: Give the plug a light
coat of sand and water, press it firmly to its seat and move it back and
forth while revolving it, lift it out a little to its seat at about
every fourth movement, and when the sand has ground down and worked out,
remove the plug, and smear over it evenly with the fingers, the ground
sand that has accumulated on the ends of the plug and barrel, then
replace it in the barrel and revolve as before until the plug moves
smoothly in the barrel, bearing in mind that if at any time the plug,
while being revolved in the barrel, makes a jarring or grating sound, it
is cutting or abrading from being too dry. Finally, wipe both the barrel
and the plug clean and dry, and revolve as before until the surfaces
assume a rich brown, smooth and glossy, showing very plainly the exact
nature of the fit. Then apply a little tallow, and the job is complete
and perfect.
In place of the tallow a soft paste of good beeswax and castor oil is an
excellent application, the two being heated in order to thoroughly mix
them.
The grinding material must be frequently changed to produce smooth work,
because if the grinding cuttings accumulate in it, they will scratch and
score the work. Indeed, it is a good plan when convenient, to hold the
cock and plug under water while grinding them, and to occasionally lift
the plug out, so as to wash out the cuttings.
The surface of a well-ground plug will be in all cases polished, and not
have that frosted appearance which exists so long as active grinding is
proceeding, and all that is necessary to produce this polish is to well
work the plug in its barrel while keeping it quite clean.
[Illustration: Fig. 2475.]
FITTING BRASSES TO THEIR JOURNALS.--Brass bores always require fitting
to their journals after having been bored, because the finished hole is
not a true circle, but too narrow across the joint face, as at F in Fig.
2475, in which the full lines represent the form of the brass before,
and the dotted line its form after being bored and released from the
pressure of the devices or chuck that held it while it was being bored.
This almost always occurs to a greater or less degree, and it arises
from local strains induced from the unequal cooling of the casting in
the mould, which strains are released as the metal is removed (in the
process of boring) from the surface of the bore. It would appear,
however, that if the finishing cut taken by the boring cutter be a very
fine one it should leave the hole true and round, but the pressure which
is placed upon the bearing to hold it against the force of the cut
prevents the bearing from assuming its natural form until released from
that pressure.
If a bearing be bored to very nearly its finished size and first
released altogether from the pressure of the holding chuck, or other
device, and then re-chucked, it is probable that the finished bore would
be practically quite round and true, but such re-chucking is not the
usual practice.
Suppose, however, that the bearing shown in Fig. 2475, be properly
fitted to a journal, still improper conditions arise from wear, because
the area of the surface D becomes from the weight and from vibration
condensed, and finally it stretches, causing the bore at F to close upon
the journal and bind it with undue friction.
[Illustration: Fig. 2476.]
If the shape of the bedding part of the brass, or bearing, be such as
shown in Fig. 2476, the surfaces A B and C will condense and stretch,
closing the diameter of the bore at E and making the sides G G fit
loosely in their places. It is to be observed that a similar
condensation of the metal occurs to some extent around the bore of the
bearing; but this surface is being continuously worn away by the
journal, and it is, therefore, at all times less stretched and condensed
than that on the bedding surface.
[Illustration: Fig. 2477.]
There is, therefore, a constant action causing the brass to bind unduly
hard at and near its joint face E, Fig. 2476, and thus to cause heating
and undue abrasion and wear. To prevent this it is necessary to ease
away that part of the brass bore, as is shown in Fig. 2477 from J to K,
clear of the journal.
But in the case of bearings receiving thrust, as in engine main
bearings, the line of pressure is in a horizontal direction; and hence
the most effective bore area to resist that pressure has been removed.
Furthermore, the bearing area of the brass bore has been reduced, thus
increasing the pressure per square inch on the remaining area.
[Illustration: Fig. 2478.]
The methods employed to avoid this evil are as follows:--In the form
shown in Fig. 2478 the joint faces are at an angle instead of being
horizontal and parallel to the line of the thrust, or the joint faces
may be made to stand at a right angle to the line of journal thrust, so
that the crown of the brass will receive the thrust. But the brasses
will still close across the joint faces (as already described) as the
wear proceeds, and the areas from J to K in Fig. 2477, must still be
eased away, requiring frequent attention and giving a reduced bearing
area. Furthermore, in proportion as the line of the joint faces of the
brasses is at an angle to the line of thrust, the strain on the top or
cap brass will fall on the bolts, so that if those joint faces be at a
right angle to the line of thrust, the whole strain of that thrust will
fall on the bolts that hold the cap and cap brass.
[Illustration: Fig. 2479.]
Another plan is to make the bearing in parts, as in Fig. 2479, in which
the top and bottom parts of the bearing extend to the joint face on one
side, but admit a chock or gib, A in the figure, which may be adjusted
by a set-screw as shown. By this means the bearing area may extend all
around the bore. In some cases two of such chocks and set-screws, one on
each side of the journal, are employed.
[Illustration: Fig. 2480.]
In place of the set-screws, whose ends, from receiving the pressure of
the thrust, are apt to imbed themselves into the chock and to thus
loosen the adjustment, wedges lifted by bolts passing up through the
cap, as shown in Fig. 2480, are employed, being preferable to the
screws.
In the Porter Allen engine the wedges pass clear through the bearing, as
in Fig. 2481, so that they may be pushed up after the manner of a key
and their pressure against the side chocks judged independently of the
nuts at the top.
In some designs the top and bottom parts of the bearing are free to move
in the line of the thrust, and the side chocks or blocks alone are
relied on to resist the thrust.
When the brasses are in two halves, they may be fitted so as to have a
known degree of bearing pressure upon the journal, and the fit may thus
be accurately adjusted, in which case they will wear a long time before
requiring re-adjustment. On the other hand when the side chocks are used
the wear in the line of the thrust may be taken up as it proceeds. In
one case the attending engineer cannot alter the fit of the bearing nor
the alignment of the shaft, while in the other he can do both. Thus the
facilities that enable him to make these adjustments properly also
enable him to make them improperly. But this would be of no consequence,
providing it could be determined whether the adjustment were improving
the conditions without first making it. With an engine at rest it is
easy to determine, by means of the connecting rod, whether the chock
adjustment is correct, so far as the adjustment of the shaft is
concerned, but it is not easy so to determine the pressure of the chock
on the journal; nor when each chock has two adjusting screws is it easy
to determine when they both bear alike.
[Illustration: Fig. 2481.]
When the bearing is in four pieces, and three of them have two screws
each, it is still more difficult to operate all so as to have the
bearing equal on the journal. The fit to the journal can only be
determined by the results: if too easy, the bearing pounds; if too
tight, the bearing heats and wears.
But undue wear may take place without heating, and this is one of the
greatest objections to this method of adjustment.
[Illustration: Fig. 2482.]
A design of bearing used in American locomotive practice is shown in
Fig. 2482. Here the joint faces C, B of the brass is bevelled, fitting
into a corresponding bevel in the box, which prevents the brass from
closing across the joint face; hence, the bearing on the journal may
extend all around the brass bore from the oil cavity A to the edges B C.
The brass is, in this case, forced to its place in the axle box under
hydraulic pressure, and this pressure springs the box open at H, making
it wider; but when the box is put to work the brass compresses somewhat,
and its surfaces conform more closely to the bedding surface of the box
than when first put in, and this causes the box to close slightly at H.
To prevent this closure from carrying the brass with it and close it
across the joint face (as in the case of the brass shown in Fig. 2476)
the following plan is adopted. The brasses, after having been turned in
the lathe, are filed along the entire surface (on each side) for a
distance of about 1-1/2 or 2 inches, so as to clear the bore of the box
near the bevels B, C. When the box is put into the hydraulic press, to
have the brass forced in, a centre-punch mark J is made, and part of a
circle L L is struck; when the brass is home in the box the arc of
circle K is made, the distance between K and L showing how much the box
has been sprung open by the brass; the amount allowed is about 1/32 of
an inch. If, as the brass is pressed in, it is found that this will be
exceeded, it is taken out and eased. When the engine is running and the
boxes spring to some extent they do not carry the brass with them,
because the sides being eased away gives liberty to the box to come and
go slightly; the bevels also tend to keep the brass bore open.
Here, then, the brasses may be fitted to align the axle perfectly, and
it is not permitted to the engineer to alter that alignment, while at
the same time the fit of the brass to the journal being made correct,
the engineer cannot alter it. Under these conditions the whole area of
the brass is effective in holding the journal, which increases the
durability of the brass by keeping the pressure per square inch on the
brass bore at a minimum.
If side chocks are used, however, it is better to set them up by wedges
than by screw bolts, because from the tightness of the fit of such
screws in the tapped holes, it is difficult to determine, with
precision, with what degree of pressure the chocks are forced against
the journal. Furthermore, the screws may not fit with an equal degree of
tightness; hence, when screwed up with an equal degree of pressure, one
end of the same chock may be set tighter to the journal than the other
end, and any undue pressure of fit at either end tends to throw the
shaft out of line as well as inducing undue wear. But when wedges are
used to set up the side chocks the nuts operating those wedges may be an
easy fit without fear of their becoming loosened (as set-screws in the
line of thrust are apt to do).
On the fast engines of the Pennsylvania Railroad solid bronze boxes,
without brasses, are used, and when the boxes require truing from having
cut or from having worn oval they close them under a steam hammer,
closing the bore across and enabling it to be trued out in the lathe
without taking much metal out of the crown of the bore. The wedges and
adjusting shoes are thickened when this becomes necessary by reason of
the box closure or width.
If a brass bore does not bed fully and equally over the entire intended
bearing area the part not fitting will at first perform no duty as
bearing area, and the whole strain will be thrown upon a less area than
is intended by the construction, causing undue abrasion until the brass
bore has what is termed worn down to a bearing. The amount of this
wearing down to a bearing may be so small as to be scarcely perceptible
to ordinary observation, but if the oil that has passed through the
journal be smeared upon stiff white paper, as writing paper, it will be
found to contain the particles of abraded metal, which will be plainly
distinguishable. Under these conditions the journal will have a dull,
though perhaps a smooth appearance, and will not have that mirror-like
surface which is characteristic of a properly fitted and smooth working
bearing, while under a magnifying glass the journal will show a series
of fine rings or wearing marks. It is necessary, therefore, that each
brass be properly fitted to its journal so that it shall bed fairly and
evenly over all the area of its bore that is intended to bear upon the
journal.
The most expeditious method of fitting a new bearing box or brass to its
journal is to first file the bore until it fits the journal when simply
placed thereon by hand, and without going to the trouble to put the
brass or the journal in position in the frame which holds them. So soon,
however, as the crown of the brass beds to the journal along its whole
length, the brass should be placed in its box, or in the frame, and the
journal adjusted in its place and rotated so as to leave its bearing
marks upon the brass bore, to assist which it may have a faint coat of
red marking on its surface. The fitting should be continued both with
file and scraper until the whole area of the part intended to bed fits
well and is smooth and polished. To produce this result the finishing
should be done with a very smooth half-round file, draw-filing so as to
leave the marks in a line with the circumference of the bore, and
finally with a half round scraper, which will remove the file marks. The
degree of contact should be such that, when the bearing is bolted up,
brass and brass, as it is termed (which means that the joint faces of
the brasses are held firmly together), the journal will rotate as freely
as when the top brass is removed, while the contact marks on the top
brass have been removed by scraping. By this means the fit will be just
sufficient to permit the lubricating oil to pass between the journal and
the bearing, and the journal will work freely and easily without any
play, knock, or pound. If, when the top brass or bearing is bolted home
and the shaft is rotated by hand, that brass on removal shows contact
marks on its bore, although it may rotate comparatively easily it will
be so tight a fit that the oil cannot pass, and as a result the wear,
instead of producing a glossy surface, will produce a dull one, and
undue abrasion will ensue even though no rings appear.
When brasses are held in rods that connect two journals together the
fitting of the brass bore must be conducted with a view to have the
brasses fit their journals all over the intended bearing area of their
bores, which can only be accomplished by trying the brass bores to their
journals while in the rod, in the manner to be hereafter described with
reference to connecting rods and to lining engines.
When a journal is worn in rings, or so rough as to cause destructive
abrasion and undue friction, it may be refitted as follows:--First, with
a smooth file draw-file the journal in the direction of its length,
taking off all the projecting rings. Then sweep a very smooth file that
is somewhat worn (which will cut smoother than a sharp file) around the
circumference of the journal so that the file marks will be in the plane
of revolution. Then wrap a piece of fine and somewhat worn emery paper
around the journal, and wrap around it (say twice around) a piece of
coarse string, leaving the two ends about two feet long. Take one end of
the string in each hand and pull first one end and then the other,
causing the emery paper to revolve around the journal and smooth it.
To refit the bearings, first with a smooth half-round file remove the
rings or rough surface, and then fit the surface with the file, so that
when in its place the journal is rotated the contact marks show a proper
bearing. Then draw-file the bore with a smooth half-round file and
finish with a half-round scraper, easing away the high spots until the
bore shows proper contact and is smooth. A piece of fine emery paper may
then be wrapped around a half-round file and the surface smoothed with
the emery paper moved across the bore and not in the direction of the
circumference of the same. The emery paper should be well worn for the
finishing and of a fine grade number, so as to leave a bright polish and
not dull marks.
In some practice the bores of brasses are left rough-filed, the file
marks being lengthways of the bearing of bore. If the journal requires
smoothing it is draw-filed lengthways of the journal. The philosophy of
this is, that the file marks will hold the oil and afford unusually free
lubrication while the bearing and journal are wearing down to a bearing.
But where the framework holding the bearings and journals are rigid,
these bearings and journals may, with care, be fitted to a polished and
equal bearing, leaving a smoother surface than that produced by wearing
down to a bearing. But if, as in the case of a locomotive, the framework
is subject to torsion, rough surfaces left to adjust themselves are
possibly better than those accurately fitted, because the whole
framework holding the bearings changes its form when the full load is
upon it and after put to work, and the fitting done when there was no
load upon the parts is no longer quite correct. The lubrication of the
bearing, however, should be very free, and the effort appears at present
to be to afford more ample oil ways than hitherto even at some sacrifice
of bearing area.
LEAD-LINED JOURNAL BEARINGS.--If a journal is worn in grooves or
undulations it becomes impracticable to properly fit the brass to it
without reducing its diameter to remove the rings, and to obviate the
cutting and heating which necessarily follow, as well as to obviate the
necessity of fitting the brasses at all, Mr. D. A. Hopkins introduced
lead-lined bearings; the lead lining being merely auxiliary to the
bearing proper, which is made preferably of hard bronze, and to which
the thin layer or facing of lead is firmly attached by a soldering
process, so that the two metals are virtually one piece. Into this lead
facing the journal, under the pressure of the car, moulds or imbeds
itself from the start, and afterwards gradually wears its way through it
into the hard metal. The perfect fit thus secured under all conditions
of the journal, aided with proper lubrication, not only prevents
heating, but secures the full wear of the brasses, and makes them at all
times perfect counterparts of the journal surfaces.
[Illustration: Fig. 2483.]
Fig. 2483 shows at the top an unfitted bearing without the lead lining,
resting upon a worn and badly-cut journal, the only points of contact
being near the ends. For obvious reasons such a journal is sure to run
hot.
The engraving below shows the application of the lead lining to the same
journal, the dark shading between the journal and bearing representing
the lead which has been pressed into the worn and hollow surface of the
journal, forming a complete bearing and distributing the weight equally
upon its surface.
[Illustration: Fig. 2484.]
Fig. 2484 represents an end view of an unfitted journal and the same
lead lined.
The lead compresses until the brass meets the journal and thus permits
between the two contact over the area that does fit or touch; while the
lead fills the remaining area of the brass bore, giving it a bearing on
the journal, thus relieving the touching points from receiving the whole
weight of the load, and preventing the cutting or abrasion that would
otherwise occur. As, however, the wear takes place the lead compresses,
permitting the journal and brass to come into bearing over its full
area, being obviously effective providing the bearing be kept free from
grit, which would imbed in the bearing and cause it to unduly wear the
journal.
If a brass is too tight a fit upon its journal, heating and abrasion, or
"cutting" as it is termed, ensues. But if a brass or box does not fit
close to its journal, lost motion and sometimes knocking or pounding
ensues. When the joint faces of brasses abut, or come brass and brass as
it is termed, they should be a proper fit to the journal when they are
keyed, or otherwise set up close together; hence there is no danger of
either having a pound in the brass, or of heating and cutting. The
objection to this plan is that the brasses must be removed from their
boxes and the joint faces filed away to let the brasses together, to
take up the wear; hence, in positions in which it is difficult to get
the brasses out, the joints should be left open, while in all cases
where they can be readily removed they should be made brass and brass.
It is to be observed that brasses that come brass and brass require less
adjusting and last longer than those left open, because the latter often
suffer from the abrasion due to an improper adjustment.
In brasses that are left open, it is not an uncommon practice to adjust
the fit as follows: Between the brass joint faces at each of the four
corners a piece of lead wire is inserted; the brasses are keyed as close
home as can be upon the journals, which compresses the lead wire; the
top brass is then released until the piece of lead wire can be moved
freely between the brass joints.
[Illustration: Fig. 2485.]
[Illustration: Fig. 2486.]
A compromise between the brass and brass and the open joint is sometimes
effected by the insertion of slips, as shown in Fig. 2485 at A, B. These
slips may be taken out by simply removing the top brass, while their
reduction of thickness lets the brasses together to take up the wear.
The thickness for these strips may be readily obtained by means of the
pieces of lead wire used as already described.
In the case of large brasses which come brass and brass, much of the
filing on the joint faces to let them together may be saved by reducing
their thickness and area by cutting away part of the metal, as at A A in
Fig. 2486.
[Illustration: Fig. 2487.]
To enable the removal of bearings for renewal, or to refit them without
taking the shaft out, various forms of construction are employed, of
which Fig. 2487, which shows a main bearing, is an example.
Thus, when the cap is removed the side chocks, or gibs as they are
sometimes called, can be lifted out by eye-bolts screwed into the holes
at _c_; the weight of the shaft can then be sustained while the bottom
piece D is removed.
A great deal of trouble in fitting journals and bearings may be avoided
if the best conditions are observed in their manufacture. If, for
example, the conditions of casting are uniform, and the diameter of the
bearing bore and journal bores are constant, that is to say, when a
great number of pieces are to be bored, the amount the bearings will
close across the joint being definitely determined, the conditions of
boring may be made such as to allow for the closure, and the fitting in
this respect may be facilitated; but this applies to small bores only,
as, say, three inches and less in diameter, because in larger diameters
there will be sufficient variation in the amounts of contraction across
the joint face to render it necessary to fit to some extent at least the
bores to their journals.
In some cases slips of paper are placed between the joint faces of the
bearings, or if the joint faces do not meet, slips of brass may be
placed between them; or again the conditions of chucking or holding the
bearings to bore them may be such as to hold them a certain amount
farther apart than they will require to be when on the journal. The bore
is then made sufficiently larger than the diameter of the journal that
it will be as nearly as possible round after being removed from the
boring machine, and will bed down fairly upon the journal without being
fitted with a file, which saves considerable labor. But unless the
bearings are so held as to be to some extent self-adjusting for
alignment, there is liability of the axis of the bore not being quite
true with the axis of the journal, the amount being so small as to
escape detection save by trial for fit with the shaft, and the bearings
in their respective positions. It is a difficult matter, in the absence
of special holding devices, to chuck a bearing, especially if a long
one, so true in a boring machine or lathe as to insure that its bore
shall stand in absolutely correct alignment with the journal when placed
in its position in the framing where it is to operate, and it is for
this reason that many bearings are bored while in their frames. In some
cases, however, this difficulty is overcome by so constructing the bores
and the pieces holding them that the boxes may swivel and adjust
themselves, as in the case of the bearings of line shafting.
Examples of the oil cavities for bearings are given as follows:--
For journals of small diameter oil cups screwing into the bearing cups,
with feed-regulating devices, are generally used, and the same are used
in the case of two half-brasses. But if the journals are of large
diameter, as, say, 5 inches or more, oil receptacles are often cast in
the caps.
In the absence of side chocks in the bearing all the oiling usually
proceeds from the top, save perhaps that an oil groove may be provided
in the crown of the bottom brass.
Fig. 2488 represents a bearing lubricated from the top and bottom; thus
in the cap is an oil cup or cavity from which passes nearly down to the
bearing a brass tube containing cotton wick, which slowly feeds the oil
to the bearing.
Fig. 2489 represents this tube and wick removed from the bearing. This
plan of feeding is largely used on marine engines and on locomotives.
When used upon stationary bearings the cotton wick need not fill the
tube, but if used on reciprocating parts it should fill so that the oil
may not spill over and pass too freely down the tube. In either case,
however, it is desirable to twist in the cotton a piece of fine copper
wire, and bend the ends over the top of the tube to keep the wick in
place in the tube.
[Illustration: Fig. 2488.]