The teeth are ground so that their tops form a true circle, this
grinding being done after the reamer has been hardened and tempered,
because in these processes the reamer is apt to get both out of round
and out of straight.
[Illustration: Fig. 2262.]
In some practice the reamers are formed as shown in Fig. 2262, and are
made in sets of three for each size; the first is slightly taper from
end to end, the second is slightly tapered at the entering end for a
length about or nearly equal to the diameter, and the third is parallel
and rounded on the end like the second, and in many cases only three
teeth are employed.
[Illustration: Fig. 2263.]
[Illustration: Fig. 2264.]
Fig. 2263 represents a reamer in which the distance between the cutting
edges A B, Fig. 2264, is greater than between B C, and so on, the
spacing decreasing from tooth A to tooth _a_. The spacing of _a_, _b_,
&c. to _f_ on the other side is also irregular, so that if the reamer be
given half a revolution no two teeth will have arrived at similar
positions except A and _a_, the former arriving at the position occupied
by the latter.
Now suppose that a hole to be reamed has a hollow or spongy seam along
it, and if the reamer be regularly spaced, there will at this point
occur a lateral movement of the reamer that will impair the roundness of
the hole, and this lateral movement the irregular spacing tends to
prevent.
If a solid reamer is made to standard gauge diameter when new, and the
bolts or pins turned to standard diameter, then by reason of the wear of
the reamer the work will become gradually a tighter fit and finally will
not go together, hence the reamer must be restored to standard diameter,
which may be done by upsetting the teeth with a set chisel. Furthermore
the workman's measuring gauges are themselves subject to wear, those for
measuring the pins wearing larger and those for the holes wearing
smaller, and this again is in a direction to prevent the work from
fitting together. It is preferable, therefore, to employ adjustable
reamers.
Thus Fig. 2265 represents an adjustable reamer in which the teeth fit
tightly into dovetail grooves, that are deeper at the entering than at
the shank end of the reamer, so that by forcing the teeth up the grooves
towards the shank the diameter is increased.
Both castings and forgings are found to alter somewhat in shape in
proportion as their surfaces are removed by the machine tools, so that
the shape of the work undergoes continuous alteration.
Suppose, for example, that a piece of metal two inches square and four
inches long, has a hole cast in it of an inch in diameter, and when
finished it is to be 1-3/4 inches square, 3-3/4 inches long, and have a
hole 1-1/8 diameter. Let it be chucked in a lathe or shaping machine and
have its surfaces cut down to the required dimensions. Removing the
metal to true the first surface will reduce the strain on that side of
the casting and alter the shape of the whole body, but this alteration
of form will not occur to its full extent until the piece is removed
from the pressure of the chuck jaws, or other clamping device holding it
in the machine, because this pressure holds it; as a result the surface
will not be so true after leaving the machine as it was before. On
surfacing the second side of the piece, the internal strain is still
further reduced, and a second alteration of form ensues, and so on at
the surfacing of every side of the piece. Now let the piece be chucked
true to have the hole bored out, and the removal of the metal in the
hole will again reduce the internal strain and the form of the body will
again alter.
Suppose, however, that the piece after having its surfaces thus removed,
and its hole bored as true as may be, were again trued over each
surface, and in its bore there will still be at each surfacing and at
the boring an alteration of form, although it may be to a very minute
degree, and from these causes the use of the reamer for work requiring
to be very true becomes indispensable.
[Illustration: Fig. 2265.]
[Illustration: Fig. 2266.]
Fig. 2266 represents a taper hand reamer with straight flutes. It is
preferable, however, to give the flutes a left-hand spiral, as was
explained with reference to reamers for lathe work.
[Illustration: Fig. 2267.]
The frames of large machines are frequently composed of parts that are
bolted together after having the holes for shafts, &c. bored, and to
insure the alignment of these holes after the frames are put together a
hand reaming bar, such as in Fig. 2267, is employed, A and B being two
shell reamers fastened to the bar by a pin.
[Illustration: Fig. 2268.]
Reamers are sometimes employed to enlarge holes or bring them fair one
with another, without reference to their being precise to a designated
diameter; thus Fig. 2268 represents a half-round reamer of the form used
by boiler makers to bring rivet holes fair, and sometimes by machinists
to ream the holes for taper securing pins. The flat face is cut down to
below the centre line, so that the back requires no clearance ground
upon it.
[Illustration: Fig. 2269.]
The square reamer shown in Fig. 2269 is used for rough work generally,
although with careful grinding and use it will produce excellent results
upon work of small diameter. Brass finishers generally prefer a square
reamer to all others for reaming the bores of brass cocks, &c., and some
of them prefer that one edge only be sharpened to cut, the other three
being oilstoned off so as not to cut, but simply serve as guides. The
square reamer is very easily sharpened whether by grinding or
oil-stoning; the flat sides are operated on, taking care to keep them
straight and the thickness even on the two diameters, so that, the sides
being straight and the reamer square, it will cut taper holes whose
sides will be straight. If the reamer is not ground square, two only of
the edges will be liable to have contact with the work bore, causing the
reamer to wabble, and rendering it liable to break.
[Illustration: Fig. 2270.]
Another and very good form of reamer for the rapid removal of metal is
shown in Fig. 2270, having three teeth and a good deal of clearance,
which enables it to work steadily and cut freely.
CHAPTER XXVI.--VICE WORK--(_Continued_).
In most of the operations of the machine-shop, the work of the chisel is
followed by that of the file; hence, as an example in the use of the
chisel independent of that of the file, the cutting of the teeth upon
files may be given as follows:--
[Illustration: Fig. 2271.]
[Illustration: Fig. 2272.]
[Illustration: Fig. 2273.]
[Illustration: Fig. 2274.]
The largest and smallest chisels commonly used in cutting files are
represented in two views and half size in Figs. 2271 and 2272. The first
is a chisel for large rough files; the length is about 3 inches, the
width 2-1/2 inches, and the angle of the edge about 50°; the edge is
perfectly straight, but the one bevel is a little more inclined than the
other; this chisel requires a hammer of about 7 or 8 pounds weight. Fig.
2272 is the chisel used for small superfine files; its length is 2
inches, the width 1/2 inch; it is very thin, and sharpened at about the
angle of 35°; it is used with a hammer weighing only 1 or 2 ounces; as
it will be seen, the weight of the blow mainly determines the distance
between the teeth. Other chisels are made of intermediate proportions,
but the width of the edge always exceeds that of the file to be cut. The
first cut is made at the point of the file; the chisel is held in the
left hand, at a horizontal angle of about 55° with the central line of
the file, as at _a_ _a_, 2273, and with a vertical inclination of about
12° to 4° from the perpendicular, as represented in Fig. 2274, supposing
the tang of the file to be on the left-hand side. The following are
nearly the usual angles for the vertical inclination of the chisels,
namely: For rough rasps, 15° beyond the perpendicular; rough files, 12°;
bastard files, 10°; second-cut files 5°, and dead-smooth-cut files 4°.
The blow of the hammer upon the chisel causes the latter to indent and
slightly to drive forward the steel, thereby throwing up a trifling
ridge or burr; the chisel is immediately replaced on the blank, and slid
from the operator until it encounters the ridge previously thrown up,
which arrests the chisel or prevents it from slipping farther back, and
thereby determines the succeeding position of the chisel. The chisel
having been placed in its second position, is again struck with the
hammer, which is made to give the blows as nearly as possible of uniform
strength, and the process is repeated with considerable rapidity and
regularity, 60 to 80 cuts being made in one minute, until the entire
length of the file has been cut with inclined parallel and equidistant
ridges, which are collectively denominated the "first course." So far as
this one face is concerned, the file, if intended to be single-cut,
would be then ready for hardening, and when greatly enlarged its section
would be somewhat as in Fig. 2274.
The teeth of some single-cut files are much less inclined than 58°;
those of floats are in general square across the instrument. Most files,
however, are double-cut, and for these the surface of the file is now
smoothed by passing a smooth file once or twice along the face of the
teeth, to remove only so much of the roughness as would obstruct the
chisel from sliding along the face in receiving its successive
positions, and the file is again greased. The second course of teeth is
now cut, the chisel being inclined vertically as before, or at about
12°, but horizontally about 5° to 10° from the rectangle, as at _b_ _b_,
Fig. 2273. The blows are now given a little less strongly, so as barely
to penetrate to the bottom of the first cuts, and consequently the
second course of cuts is somewhat finer than the first. The two series
of courses fill the surface of the file with teeth which are inclined
toward the point of the file. If the file is flat and to be cut on two
faces, it is now turned over; but to protect the teeth from the hard
face of the anvil a thin plate of pewter is interposed. Triangular and
other files require blocks of lead having grooves of the appropriate
sections to support the blanks, so that the surface to be cut may be
placed horizontally. Taper files require the teeth to be somewhat finer
toward the point, to avoid the risk of the blank being weakened or
broken in the act of its being cut, which might occur if as much force
were used in cutting the teeth at the point of the file as in those at
its central and stronger part. Eight courses of cuts are required to
complete a double-cut rectangular file that is cut on all faces, but
eight, ten, or even more courses are required in cutting only the one
rounded face of a half-round file. There are various objections to
employing chisels with concave edges, and therefore, in cutting round
and half-round files, the ordinary straight chisel is used and applied
as a tangent to the curve. It will be found that in a smooth,
half-round file 1 inch in width, about twenty courses are required for
the convex side, and two courses alone serve for the flat side. In some
of the double-cut, gullet-tooth saw-files, as many as twenty-three
courses are sometimes used for the convex face, and but two for the
flat. The same difficulty occurs in a round file, and the surfaces of
curvilinear files do not therefore present, under ordinary
circumstances, the same uniformity as those of flat files.
[Illustration: Fig. 2275.]
The teeth of rasps are cut with a punch, which is represented in two
views, Fig. 2275. The punch for a fine cabinet rasp is about 3-1/2
inches long and 5/8 inch square at its widest part. Viewed in front, the
two sides of the point meet at an angle of about 60°; viewed edgewise,
or on profile, the edge forms an angle of about 50°, the one face being
only a little inclined to the body of the tool. In cutting rasps, the
punch is sloped rather more from the operator than the chisel in cutting
files, but the distance between the teeth of the rasp cannot be
determined, as in the file, by placing the punch in contact with the
burr of the tooth previously made. By dint of habit the workman
moves--or, technically, hops--the punch the required distance; to
facilitate this movement, he places a piece of woollen cloth under his
left hand, which prevents his hand from coming immediately in contact
with and adhering to the anvil.
As an example in the use of the chisel for chipping purposes, let it be
required to fasten a feather on a shaft.
There are four methods of inserting feathers: First, a shaft may have a
parallel recess sunk into it and a parallel feather may be driven in;
second, the feather may be made slightly taper and driven in; third, the
feather may be dovetailed on the sides and ends both, or on the ends
only, and as one or the other of these is the proper method, and the
process is the same for both, one only need be described.
[Illustration: Fig. 2276.]
[Illustration: Fig. 2277.]
[Illustration: Fig. 2278.]
In Fig. 2276 let S represent a shaft and F a feather, required by the
drawing to be permanently fixed therein. The drawing will not, in
ordinary shop practice, give any instructions as to how the feather is
to be fastened; hence the mechanic usually exercises his own judgment
about the matter, or is governed by the practice of the shop. If left to
his own judgment he may determine to so fix it that it may be locked on
all four sides, as in Fig. 2277, or he may simply set it in as in the
similar views shown in Fig. 2278.
The method shown in Fig. 2277 is the most secure and best job; but, on
the other hand, it is the most difficult and costly. The difficulty
consists in filing the parallel part above the surface of the shaft to a
line that shall be quite even with the surface of the shaft. This
difficulty may be overcome by leaving the sides parallel, and making the
length A equal to the length of the acting part of the key, and the
bottom B as much longer as may be required to get the required amount of
dovetail on the feather ends.
[Illustration: Fig. 2279.]
[Illustration: Fig. 2280.]
[Illustration: Fig. 2281.]
[Illustration: Fig. 2282.]
The first thing to do is to mark off the keyway by scribing lines on the
surface of the shaft, indicating the location for the feather seat; and
for this purpose nothing is better than the key seat rule shown in Fig.
2279, in which W is the key seat rule, and S the shaft. After the lines
are drawn they should be defined by centre-punch dots, as in Fig. 2280,
and then the metal should be cut out on the sides first, using a cape
chisel, and cutting close to the side lines, as in Fig. 2281, in which A
is a cape chisel cut taken along one side, D a second cape chisel cut,
being carried along the other side, C the cape chisel, C´ the cut taken
by the chisel, and B a piece of metal to be cut out after the cape
chisel has done its work. Suppose, now, the mass of the metal is
removed, then the dovetailing is performed as follows: Next the
_setting_ or _upsetting_ is proceeded with as shown in Fig. 2282, which
is a side sectional view. S is a set chisel driven by hammer blows
against the walls of the feather seat (as against the end _e_), causing
it to bulge up, as shown at _f_. This setting will enlarge the feather
seat or recess, so that the wide part of the dovetail on the feather
will just pass in (the dotted lines shown in Fig. 2281 having, of
course, been marked to the size of the feather, where it will, when
fixed, meet the surface of the shaft). The feather is then placed in its
seat and bedded properly by red marking applied to its bottom surface to
show the high spots on the seat of the recess, and when properly bedded
it is fastened, as in Fig. 2283, in which S is a set chisel, which, by
being struck with hammer blows, closes the bulged metal back again on
the dovetail of the feather, and firmly locks it in the shaft. And all
that remains is to file the shaft surface around the feather level with
the surrounding surface, there being usually a little surplus metal from
the upsetting.
[Illustration: Fig. 2283.]
[Illustration: Fig. 2284.]
[Illustration: Fig. 2285.]
[Illustration: Fig. 2286.]
[Illustration: Fig. 2287.]
As an example of chipping and filing let it be required to chip and file
to shape and to fit a knuckle joint (or a double and single eye, as it
may more properly be termed), such as in Fig. 2284. The eye being marked
out by lines, the first operation will be to remove the surplus metal
around the edges by chipping, which should be done (with the pin in
place, so that it may support the eye) before the joint faces are filed
at all, and should be carried in a direction around the eye, as shown in
Fig. 2285, in which _v_ is the vice jaw, E a lead clamp, C the cut, and
D the chisel. By chipping in this direction two ends are served: first,
the force of the chipping blows is less likely to bend the eye if it is
a light one, and, secondly, the chipping will not break out the metal at
the edge of the eye, which it would be apt to do if the chipping was
carried across. This is shown in Fig. 2286, where a chisel cut is
supposed to have been carried across from A to B and a piece has broken
out at B. If the width of the eye is too broad for one chisel cut, a
cape chisel should be run around it, as in Fig. 2287, A D showing the
cutting, the flat chisel cuts B, C being taken separately afterwards.
In order to illustrate the filing clearly, it will be necessary to show
more metal to be filed off than would be the case in practice, unless
the eye were very small, in which case it would not pay to chip.
[Illustration: Fig. 2288.]
Put the eyes together with the pin in and let the two lowest places on
the edges coincide. Then file a flat place clear across them, as shown
in Fig. 2288 at F, making it parallel to the pin, and, say, down to
within 1/100 of the finished depth. To test the parallelism of the flat
place, take out the pin and apply to the flat place a square, rested
against the radial face of the double eye, or measure its distance from
the hole of the eye on each side of the double eye, that is at each end
of the hole.
[Illustration: Fig. 2289.]
When it is true and down to the required size, put the eyes together and
let their relative positions be such that the flat places do not
coincide, and that on the double eye will serve as a guide to carry the
filing around the single eye, while that on the single eye will serve as
a guide to carry the filing around the double eye, as will be seen on
reference to Fig. 2289, in which the flat places A, B on the double eye
serve as a guide to file C down to, while the flat place on the single
eye at D is a guide to file the metal at E, F down to, and it is obvious
that by moving the eyes to different positions the eye may on that side
be filed true and to circle.
When the filing has thus been carried around as far as the movement of
the eyes permits on that side, turn the single eye over in the double
eye, and they will appear as shown in the end view, Fig. 2290, A being
the filed side of the single and E D that of the double eye; hence the
metal at C, B must be filed down level with A, and that at F down level
with E, D.
[Illustration: Fig. 2290.]
We have assumed that the edges only required finishing irrespective of
the joint faces; but let it be assumed that the whole of the eye has
been dressed up by machine tools, and that it requires fitting and
finishing by the file both on its joint faces and on its edges.
If the eye has been bored and faced in the lathe the faces will be about
true with the hole, but if it has had its faces trued in a machine, as a
planer or slotter, and the hole bored subsequently in a slotting
machine, the hole may not be true to the faces. This may occur from want
of truth in the chucking devices, from these devices having been held to
a table or carriage moving on slides, and having lost motion or play, in
which case from the leverage of the pressure of the boring tool-reamer
or bit, this table may have lifted to the extent of such play, in which
case the hole will not be at a right angle to the face or faces.
[Illustration: Fig. 2291.]
First, then, these faces must be tested for truth and smoothed by
filing. The best testing device is a pin and washer, the pin neatly
fitting the hole in the eye and the washer neatly fitting the pin. The
radial face of the pin head and of the washer should then be given a
light coat of marking, and be inserted in the eye, as shown in Fig.
2291, in which _a_ is the pin head and B the washer. If each be then
rotated under pressure against the eye, they will mark the high spots,
which may be filed and draw-filed until an even contact all around is
shown.
The single eye should be similarly faced and fitted, a somewhat tight
fit, into the double eye. In a job of this kind, where accuracy of fit
is essential, it is usual to bore the hole about 1/100 inch smaller than
its finished diameter, and after fitting the two eyes, to ream out the
eyes while bolted together.
For the reaming the two eyes should be clamped together. The single eye
is left somewhat too tight a fit to the double eye to permit of the
finishing being done after the holes are reamed, because the reaming may
slightly alter the axial line of the hole. The two bolts holding the
clamping plates should be brought just home on the plates, and then
tightened up gradually and alternately, so that the eyes may be gripped
fair, and not liable to move during the reaming. The bores of the eyes
should be set as true as possible one with the other before the plates
are tightened upon the eyes, for if it is attempted to set the eyes true
by hammer blows afterwards, the pressure of the plates would cause the
arm or hub of the double eye which received the hammer blow to move more
than the other, or, in other words, to spring out of its normal
position, and the eye will be distorted. But when released from the
pressure of the clamping plate the double eye will resume its normal
shape, and the holes will not be axially true in the two eyes.
After the holes are reamed the temporary pin and washer used for the
facing will be too loose, and the proper pin should be used for all
future operations. The eyes should be put together with a light coat of
marking on both faces of the single eye, and, with the pin in place, one
eye should be moved back and forth, when they may be taken apart again
and filed on the high spots. When by repetition of this process they fit
properly the outside edges may be filed up, as already described.
It is obvious, however, that the pin and washer shown in the figure may
be hardened and used to file the edges up before the reaming, in which
case, their diameters being equal, and equal to that of the required
finished diameter of the eye, it is easy to file the eye edges true and
to size; but even in this case the eyes should be finished by reversing
and moving as before described. There is, however, the objection to
filing the edges--first, that the joint will show plainer, because in
filing the side faces to fit the single into the double eye, that part
of each face near the edge is apt to be filed away slightly too much,
causing the joint to show; but if the circumferential edges of the eye
be filed last, the part so filed away is removed and the joint may be
made almost invisible.
The best plan of all is to first fit the eyes, then ream them out and
then provide a hardened pin and washer to fit the reamed hole, then file
down the circumferential edges nearly level with the pin and washer and
finish by reversing and moving the eyes as before described.
In the absence of any pin and washer, such as shown in Fig. 2291, the
inside faces of the jaws of the double eye must be filed parallel to the
outside radial faces of the single eye, the outside surfaces being trued
when the hole is bored. If none of the surfaces have been trued with the
hole, the outer ones should first be trued, using a [T]-square (if there
is no pin) to test the truth of the face with the hole, and the inside
jaw faces must be trued with the outside, measuring each jaw with
outside calipers, and the width between the jaws with inside calipers.
[Illustration: Fig. 2292.]
Let us now suppose that it were attempted to first fit the single to the
double eye a tight fit, then to ream the hole and then to make the joint
an easy working fit. In this case the finished hole in one eye may
become out of true with that in the other, that is, it may not be
parallel with that in the other, and for the following reasons:--The
holes of the two eyes will rarely come quite true with each other, even
though the radial faces of the eyes be turned in the lathe or faced in a
machine when the holes are bored, and it is the duty of the reamer to
true as well as smooth them in whatever direction they may be out of
true or face one with the other until they are put together. Now, if
they be put together a tight fit, the outside jaws are sprung open to
some extent. Again, they may be sprung slightly atwist, and if the hole
be reamed true and this twist taken out afterwards the hole will come
atwist or out of fair in proportion as the jaws lose their twist from
being fitted.
Again, reaming the hole slightly alters its axial line, and the radial
faces, if at a right angle to the hole before reaming, will not be so
after reaming, and it is not practicable to discover in just what
direction and to what degree reaming the hole will alter its axial
direction; hence, the single eye must be fitted as near as may be before
the holes are reamed, and finished afterwards as described.
Let it be required to reduce by filing, the diameter of a round pin or
to file it to fit a taper hole, and the diameter of the pin being small
it may be held by one end in the vice jaws or by means of the clamps,
shown in Fig. 2091 or those in Fig. 2092. But the filing can be more
truly and easily finished as in Fig. 2292, in which there is shown
fastened in the vice a filing block having [V]-grooves (of varying width
to suit varying diameters of work), in which the pin to be filed may be
rested.
The pin is held by the hand vice shown, and is rotated towards the
operator during the forward file stroke (one hand holding the hand vice
and the other the file), and in the opposite direction during the back
stroke. After every few file strokes the hand vice is partly rotated in
the hand so that the whole of the pin surface may be subjected to the
file. The hand vice enables the pin to be forced into its hole and
rotated, to show by the contact or bearing marks where it requires
filing to adjust the fit.
[Illustration: Fig. 2293.]
Fig. 2293 represents an excellent form of hand vice for holding pins,
&c., the jaws being pivoted to a cross piece and opened by a cone, the
handle threading to the stem of the cross piece, and being hollow so
that the work may pass through it. The work is thus very firmly gripped
and not liable to move in the jaws as it is when the hand vice is
fastened upon the work by a thumb nut.
Very thin pieces of metal cannot be well held in the vice jaws, and as
an example of this kind of work holding, let it be required to file up a
caliper leg, which being curved cannot well be held in any of the vice
fixtures heretofore shown.
[Illustration: Fig. 2294.]
In Fig. 2294 there is a block of wood having an extension at A that may
be gripped in the vice jaws. Upon the surface of the block the caliper
leg is held by brads or nails driven around its edge, as shown, or it is
obvious screws may be used.
[Illustration: Fig. 2295.]
An excellent example of filing is to file up a hexagon nut or a bolt
head. This is apparently a simple piece of work, but it is in fact a job
that requires a good deal of care and precision to properly accomplish.
The requirements are that the nut shall measure alike across the flats,
that each flat shall be parallel to the axial line of the bolt, and at a
proper and equal angle to both of its neighbors, and that the nut shall
be of equal thickness all round. The method of accomplishing this result
is as follows: Let Fig. 2295 represent a bolt head, after it has been
turned in the lathe. It will be observed that the end face of the bolt
head is rounded. Now a bolt head of this form gives a very neat
appearance, but it presents difficulties in the filing up, as we shall
see presently.
[Illustration: Fig. 2296.]
[Illustration: Fig. 2297.]
[Illustration: Fig. 2298.]
[Illustration: Fig. 2299.]
Suppose that one flat (which we will call flat A) of a nut, is nearest
to the bore, then to make the nut of equal thickness all around, the
other flats must be so filed down as to approach the bore as nearly as A
does, and it is assumed that there is metal enough to permit this. The
flat A will then be the first one to be filed up, taking off just
sufficient to make it true when tested by the nut gauge, applied as in
Fig. 2296, in which N is the nut, and G the gauge. The flat must also be
filed true when tested by the gauge, as in Figs. 2297 and 2298, the
gauge G being tried rested on A and applied to B, and then rested on A
and applied to C. A should be filed so that, if possible, it will be at
the proper angle to both B and C, but if, from errors in the angles of B
and C, this is impossible, the error should be divided between the two,
as shown, for example, in Figs. 2299 and 2300, where the gauge is shown
in the two positions necessary to test each respective flat, B and C;
the amount of error being equal at H and I.
The next flat to file will be E, Fig. 2299. Now, in a small nut, the
chamfer of the nut edge will be sufficient guide to the eye in filing E
to an equal thickness (that is, equal for distance from the bore to A).
In order that the finished nut shall be so true that the nut gauge shall
show that the flats or angles are true one with the other all around the
nut, it is necessary that the flat E shall stand parallel to A; hence it
should be made so by measurement with calipers, irrespective of its
angle to either D or F. After E is filed it will serve as a base from
which D and F may be filed to angle, while A will serve as a base from
which the flats D and C may be filed to angle; but, while testing the
angle with the gauge, C and D should be tried for parallelism, and F and
B for parallelism, while the diameters across these flats should be
equal on all sides.
[Illustration: Fig. 2300.]
If it were attempted to go all around the nut, filing to the gauge, as,
for example, filing C, Fig. 2300, from A, F from C, E from F, D from E,
and B from D, all the error in the angle of the gauge, or errors of
workmanship, will (supposing the latter to be always in the same
direction) be multiplied upon, or rather added to B when tested with A,
and these two will not be of correct angle. Again, any error made upon
one flat will be copied upon the one filed to gauge angle from it;
whereas, filing E parallel to A insures the correctness of these two,
and testing the parallelism of the others, as B, F, serves to discover
and correct any error of angle that may exist. It is obvious that in
filing each flat the gauge must be applied as in Fig. 2296, as well as
in Fig. 2298.
In filing the opposite flats to diameter to fit the wrench or gauge, if
one be used, it is best to leave them a tight fit until all are nearly
finished, so that any error that may be discovered may be corrected
while finishing them.
[Illustration: Fig. 2301.]
[Illustration: Fig. 2302.]
In small nuts, if two are to be filed, a better plan may be followed.
The two nuts may be put upon a short piece of screw, as shown in Fig.
2301, and screwed firmly together. In doing this, however, it may be
found that the nuts will not tighten against each other, with the flats
fair one with the other. This, however, may be accomplished by winding
around the piece of screw, and between the nuts, a piece of waste,
twine, or rag, and then screwing them together until they bind
sufficiently and the sides come fair; the nuts may then be put in the
vice, the jaws of the latter meeting the end A of the screw and the face
B of the nut in the figure. Select the thinnest flat on either of the
two nuts, and file it and the one coincident to it, but on the other
nut, at the same time taking care that both are filed equidistant from
the screw. To test this, apply the gauge as shown in Fig. 2296. File
these faces down a little above size, and then loose the nuts and put in
an addition of waste or twine, so that the same faces shall not
coincide, and the two filed faces will serve as guides, down to which
their new contiguous faces may be filed, the hexagon gauge being applied
as before. By adding waste or twine, this process may be repeated, the
original, or first-filed faces serving as guides down to which to file
all the others, which will insure equal thickness of all the flats.
After roughing out all the flats in this manner, reverse the nuts on the
screw, so that the two chamfered faces come together, as in Fig. 2302,
and any want of truth in the parallelism of the flats one with the
other, or with the axial line of the screw, will become at once
apparent, and will be corrected in the finishing, providing that an
equal amount be filed off the respective sides that are in the same
plane as are A and B in the figure. Of course nuts filed in this way
require the application of the calipers and gauges, the same as
described for a single nut; but uniformity will be assured and the
filing truer, because the filing in small nuts, as an inch or less, will
be more true on account of there being a larger area for the file to
rest and steady upon. It is obvious that a plain cylindrical piece,
instead of a piece of screw, may be used, in which case the waste or
twine will be unnecessary; but in this case the plug, or cylindrical
piece, should be shorter than the length of the two nuts, and should not
be so tight a fit to the bores as to damage the threads.
In small nuts it will not pay to chip off the surplus metal, because
they cannot be held sufficiently firmly in the vice without suffering
damage from the vice-jaws, or even from copper clamps, while lead ones
are too soft to hold them.
[Illustration: Fig. 2303.]
The finishing marks, if any, should be in a line with the bore of the
nut, which gives the neatest appearance. The process is the same for a
bolt head, such as shown in Fig. 2295, as for a single nut, with the
exception that the gauge must be applied as in Fig. 2303, when testing
the truth of the flats with the axial line of the bolt, this being
necessary because of the roundness of the end face A, in Fig. 2303. The
distances D and C will be equal when the flat is true in that direction.
A pair of outside calipers form an excellent example in vice work. The
material should be good cast steel of an even thickness, and therefore
(unless for very large ones) saw blade will answer the purpose. It
should be well softened by being made to a low red heat and buried in
fine cinder ashes or lime, and allowed to cool there; the proper width
of this piece of steel being sufficiently greater than the size of the
caliper washer, to allow room for a chisel cut and leave a little to
file off in truing up the joint. The length should be somewhat more than
that required to make the legs, because a piece will be required to be
cut off the narrow end to give substance enough for the points. The size
of the washer should be drawn at each end of the steel, the centre of
the washer should be centrepunch-marked, and a line should then be drawn
to set off the two legs. The steel is then severed along this line, thus
getting out the two rough legs. When shears are not at hand, or when it
is not designed to use them for this purpose, three methods of dividing
may be pursued: First, we may drill small holes along the line, and cut
between the holes with a chisel. The objection to this is that the blade
is sometimes very hard to drill. Secondly, we may make centrepunch
marks along the line, and then cut along the line with a chisel; and
thirdly, we may drill a few holes at each end, and cut the middle with
the centrepunch and chisel. The entire drilling is the safest, and the
centrepunching the most hazardous, but it can be accomplished if the
centrepunching is done lightly and gone over several times, with the
chisel applied between the centrepunch marks, which will be much the
quickest plan of the three.
The hole is next drilled for the rivet, care being taken to make it
about 1/32 inch smaller than the proper size, because the drill will not
make a sufficiently true and parallel hole, and the latter must be
reamed or trued out; and again because the legs have to go into the fire
to be bent, and hence the holes may become damaged. There is another
consideration, however, in determining the size to drill this hole,
which is that the two legs require to be riveted together to bend them,
and it is as well to drill the hole to suit the piece of metal intended
to be used for this temporary rivet, which should be of brass or copper,
so as to drive out easily after the bending is done. During the bending
process the points should be thickened, care being taken not to twist
them in the process. If the vice hand does the bending, the following
instructions are pertinent: Heat the steel slowly and turn it over and
over in the fire so that the points may not get burned before the wider
parts are sufficiently heated. Let the fire be a clean one, that is,
with no gaseous or blazing coal about it, or the coal will stick to the
sides of the calipers, and they will get cool while being cleaned of
adhering coal after being taken from the fire. Begin the bending from
the thick end, carrying it forward by degrees. Strike light but rapidly
succeeding blows, placing the steel upon the round point of the anvil.
The bending completed, and the points being thickened, the edges of the
legs are trimmed upon an emery wheel or with a file, using the latter
lengthwise of the edges if a new one, or crosswise if an old one. A full
1/32 inch may be left to trim off after the calipers are put together.
The temporary rivet may next be driven out, first, however, gripping the
legs firmly and near to the rivet end with a hand vice, putting a piece
of sheet brass between each jaw of the hand vice and the steel;
otherwise the teeth of the latter will mark the steel, entailing a great
deal of extra labor to file the marks out. The rivet hole is then reamed
out to the required size, the two legs being held together by the hand
vice to render the reaming more steady and true by making the hole
longer when the two are together.
The next operation is to turn the rivet and washers. It is a very common
practice to turn two separate washers and a rivet. On account, however,
of the small amount of bearing in the washer holes, such washers are apt
to rivet up out of fair one with the other, making an unsightly joint
and causing them to be out of round when the edges of the joint are
filed up. A better plan is to turn a pin and washer, taking care to make
the diameters of the two exactly equal and the flat faces of each quite
level. The pin should be turned about 1/64 inch taper, the small end
being made a neat fit to the holes in the caliper legs, and should be
made of cast steel properly annealed. When finished, the head of the pin
should be gripped by a pair of lead clamps in the vice, the end being
left protruding so that the legs can be put upon it and revolved back
and forth with a good supply of oil and under hard pressure, so that the
pin will be forced a good and rather tight fit into the holes. This
process will also smooth out the holes and condense the metal around
both the holes and the pin. It is well to leave the pin to fit about one
half as tight as the finished joint requires to be. The washer should be
countersunk about three-quarters of the way through the hole, the latter
being left a close working fit to the pin.
The legs should be rough filed, second-cut filed, and smooth filed
before being draw-filed, care being used to keep the files clean, so as
to avoid scratches. During this filing, however, the pin should be tried
in the hole to see if the head comes fair down upon the face; thus the
pin forms a guide and test in facing up the joint of the leg, and this
is one of its advantages over the two-washer plan. After carefully
draw-filing and polishing the sides of the legs the fitting of the joint
is finished as follows: Place the two legs upon the pin in their proper
position, and then put the washer into its place. Then behind the washer
place another temporary one that will protrude beyond the end of the
pin; then grip the whole tightly between a pair of lead clamps or pieces
of thick leather in the vice; this will bring all parts of the joint
home. Take hold of one leg in each hand and move them backward and
forward as far as the vice will let them go, repeating the operation
about a dozen times or more. This will mark the high spots upon the
legs, which may then be taken apart again and have the bright parts
removed by a scraper. It is also well to place the flat face of the
washer upon a smooth file and rub it backward and forward under finger
pressure, which will tend to correct any defect in its flatness. When
the faces of the joint bear all over, it may be put together with oil
and placed in the vice as before. Work it well back and forth, take it
apart again and cut off the rivet to the required length, taking care
very slightly to recess the end to assist the riveting. The whole joint
should then be wiped quite clean, freely oiled, and put together ready
to rivet. The head of the pin should be rested upon a block of lead, so
that it will not get damaged. The riveting should be done with a small
light ball-pened hammer, the blows being delivered very lightly and
evenly all round the edge. As the riveting continues it is necessary to
move the legs occasionally to see how the tightening proceeds, and when
the legs are sufficiently tight, one of them may be gripped between
pieces of leather in the vice, while the other is well worked and
lubricated with oil. Then the riveted end should be filed off to very
nearly its proper height and shape, and the joint well worked back and
forth and round and round in the hand until it gets quite warm, when it
may be cooled in water and tried for tightness. If too tight, it may be
either worked until easy, or the riveted end of the pin may be tapped
with a hammer to loosen it slightly. The riveting being completed, and
the end filed smooth, the rounded part of the washer and the pin head
should be draw-filed with a very fine file moved in varying directions,
and then the polishing may be done with emery paper.
FITTING KEYS.--Keys that have been planed or milled will still require
fitting with the file to insure that they bed properly. If the key to be
fitted is taper and intended to fit top and bottom, the sides should
first be filed true to a surface plate, and fitted into the keyway in
the shaft, so that it can be slid up and down a good working fit. While
fitting it, however, it is well to try it once or twice in the keyway in
the wheel, as well as in the shaft, so as to see by the marks whether
the keyways in the shaft and wheel require any fitting at all, either to
make them quite square with the outside face, supposing it to be turned
off, or to give them a good even bearing surface. The key being fitted
sideways we must give the two keyseats a coating of red marking just
sufficient to show that the surface is of a red tint, and then put the
wheel in its place on the shaft. Then we bevel off the edges of the key
at each end, leaving a chamfer of 1/16 inch, and after facing off the
top of the key with a bastard file, we place it in the keyway and tap it
very lightly to a gentle bearing. After driving the key lightly home and
taking it out again, we may file it on the top and bed it on the bottom,
according to the indication of the marking, and re-insert it, tapping it
up until it is home, top and bottom, without being a driven fit at all;
on taking it out we file it according to the marks again, and if we
continue this process until the key is a good fit, it will not spring
the wheel the least out of true, no matter how tight, reasonably, it is
finally driven. The key must never be driven in or out dry, for it will,
in that case, inevitably cut during the first part of the operation; the
marking put on the keyway is sufficient lubrication, but after two or
three insertions the key also should be itself given a light coat, which
will serve as lubrication, as well as denote the fit.
The bearing or contact marks upon a key driven home very lightly may
show at one end or on one side only, while if the key was driven farther
in those marks may show all over, making the key appear to fit much
better than it actually does. This occurs from the elasticity and
compression of the metal of the keyway and key, the metal giving most
where the contact is hardest; from this it is apparent that a wheel
truly bored and a good fit may be set out of true by the key.
In Fig. 2304, for example, is a wheel hub W, assumed to be a good fit to
the shaft S, while the key K fits at the end A only. If the key be
driven tightly home, the wheel will spring over, so that instead of the
plane of its diameter standing at a right angle to the axial line of the
shaft as at D in Fig. 2305, it will stand at an angle as at E, throwing
the wheel out of true in that direction. This would occur not only on
account of the elasticity and compression of the metal of the keyway,
but also because the surface of the bore of the wheel and of the shaft
is not, even under the best of turning, smooth enough to come into close
contact all over, but are covered with slight projections or
protuberances, which may occur in spirals because of the turning tool
marks, or in localities because of differences in the texture of the
metal. In driving the key home these protuberances give way, and they do
so most where the contact pressure is greatest, which would be at G in
Fig. 2305, causing the wheel to cant over. If the wheel is not a good
fit to the shaft it will not in this case touch the shaft at C, Fig.
2305.
[Illustration: Fig. 2304.]
[Illustration: Fig. 2305.]
[Illustration: Fig. 2306.]
Now suppose the key to bear at _a_ and _b_, Fig. 2306, only, then the
wheel would be thrown out of true in a direction at a right angle to the
length of the key as denoted by the line E, which should stand as at D.
A properly bedded key binds the opposite half of the circumference of
the wheel bore to the corresponding half circumference of the shaft; but
if the key binds at one end only, as in Fig. 2304, the contact will be
at the end H only; hence the surfaces will soon compress, on account of
all the strain of the key falling on a small area, and the key will get
loose.
It is obvious then that if a wheel has not been bored to run true the
error may be to some extent corrected in fitting the key, but in this
case the key must be driven well home, and the wheel rim tried for
running true during the fitting process, the key being so bedded as to
true the wheel as far as the elasticity and compression will permit; but
a key thus bedded will not hold so firmly.
The distance a key of a certain length, breadth, and thickness, and of a
given taper, will drive after being pushed home by hand or lightly
tapped in with a hand hammer depends upon how closely it fits to its
seat, and upon the elasticity of the metal, as well as upon the force
with which it is driven. The workman usually, while fitting the key,
drives it well home occasionally, to see how much of its length to allow
for the final driving, and while doing so, if the key is a small one, a
hand set chisel or a piece of copper should be interposed between the
key head and the hammer (a blacksmith's set chisel is used for large
keys) to prevent the hammer from damaging the key.
In fitting keys to old keyways the key is made too long, and cut off
after being driven home. A long key is apt to bend in the driving, hence
it is not unusual to support it by holding a second hammer beneath and
against it to support it while being driven. In driving a key out,
especially if it is fast home, a quick heavy blow is best, as it is less
likely to burr, swell, or bulge the end of the key. But after the key
has started lighter blows will answer.
To make a key for an old sunk keyway, it is as well to fit a piece of
wood thereto as a guide in forging and fitting the key. If a _fast_
running grindstone or emery wheel is at hand, many will forge the key a
trifle large and then grind it as near as possible, and finish by
filing. This, however, does not produce good work; it is better to plane
the key all over, leaving a little in size for fitting. In preparing the
piece of wood referred to, it should not in the fitting be driven or
even forced in and out to try the fit, for the wood will compress and
the marks mislead as to the actual fit. The proper way is to chalk the
piece of wood and push it up the keyway just tightly home, then withdraw
and fit it again.
In cases where the key is forged to very nearly the finished size, and
is finished by the file, as sometimes occurs when away from the shop, it
is best to forge the key with a gib head, as in Fig. 462, to assist in
extracting it, especially when it is difficult to drive the key out from
the back end, or when the keyway does not pass entirely through. The key
should be finished with a smooth file and with the file marks
lengthways; it is, in fact, better to use a small smooth file and
draw-file it, taking care to ease the high spots the most; and before
driving it home both it and the keyway should be oiled.
If a keyway is to be cut by hand through a bore, as in a pulley or
gear-wheel bore, its width should be marked with a [T]-square. If its
width does not exceed 1/2 inch a cape chisel a little less (say 1/32
inch less) than the finished width of keyway should be used, which will
leave a little metal for the sides to be filed true. If the keyway be an
inch wide it is better to take a cape chisel about 1/4 inch wide and cut
a groove along each side of the keyway (keeping close to the marked
line), and then cut out the middle with a flat chisel. The sides and
bottom of the keyway should be surfaced true with the file.
If a keyway is to be cut in a shaft the cape chisel should be used in
the same manner as above. But in both cases it is best, when filing, to
occasionally ease out the corners with the edge of a half-round file,
for reasons which will be explained presently.
In chipping a keyway in a bore the cut must not be carried entirely
through from one side, or the metal at the end of the cut will break
out, and even in wrought iron this is apt to occur, so that it is
necessary to cut the keyway from each end, or, at least, nick it in at
one and cut it from the other end. In long key ways it is handiest to
cut them half-way from each side, using, in the absence of anything
better, a piece of planed wood and red marking or chalk to try the
keyway with.
[Illustration: Fig. 2307.]
In cutting out through keyways by hand the location of the keyway is
marked off by lines on both sides of the stub end of the rod, and then
the mass of the metal is removed by drilling through as many holes as
can be got in the size of keyway required, as shown in Fig. 2307, in
which W is the work, B C D E the location of the keyway, and 1, 2, 3, 4
are the holes, taking care to have the drill rather smaller than the
width of requisite keyway. The holes are drilled half-way through from
each side, which is done to keep the keyway true; for if the drills were
to run a little to one side, as they are apt to do from a variety of
causes, a great deal of work would be required to correct the error.
If the keyway is of sufficient dimensions to admit of the use of a
chisel, the pieces left between the drilled holes are chipped out, and
for this purpose a side chisel is found very useful, not only to nick
the sides of the pieces left by the drilling, but also to take the
finishing chipping cuts on the sides of the keyway. To cut out the
square corners of the keyway, the diamond-point chisel shown in Fig.
2171 is employed.
[Illustration: Fig. 2308.]
If, however, the keyway is a very deep one, requiring long and slight
chisels, the chipping process may be greatly reduced, or in fact
entirely dispensed with, by plugging up the holes first drilled in the
stub end by driving pieces of round iron tightly into them, and then
drilling new holes, having their centres midway between the pieces so
driven in, as at A in Fig. 2308. After the latter drilling, the
remaining pieces of plugs are driven out, leaving the centre of the
keyway cut clear through and the sides with a series of flutes in them,
as shown at B, Fig. 2308 (in which 1 2 are the plugs and A is a centre
for the new hole at that end), which should be filed away with a file as
thick or strong as the clear space will allow. These plugs must be of
the same metal as that in which the keyway is cut, otherwise the drill
will be apt to run to one side.
To insure truth in the surfaces, a surface plate to test with is an
absolute necessity, while to test the parallelism, a small sheet iron
gauge is used, which gauge may afterwards be employed as a guide whereby
to plane the thickness of the gib and key.
In cases where a slotting machine is at hand, it is sometimes the
practice to cut out one end of the keyway to a sufficient length to
admit a slotting tool, and then to slot out the remainder. This plan is
often resorted to in getting out keyways of unusually large dimensions.
A much more usual method, however, is to employ slotting or keyway
drills.
It is obvious that the ends of the keyways cut by drills are half round;
hence, if square corners are required, they must be cut out square with
the chisel shown in Fig. 2176, and afterwards filed out true. As a
general rule, keyways cut with these drills require filing on the sides
to get proper smoothness and bearing for the keys; and here it may be
remarked that, in filing the corners of the keyway, a safe-edge file
must be used, so that the two faces forming the corner will not be
operated upon simultaneously, because that would require that the file
be used in a straight line laterally as well as horizontally, and this
is impracticable even in the hands of the most skilful.
Even the square file should have a safe edge upon it, and such an edge
is usually produced by grinding the teeth off one face of the file. In
selecting the face to have the teeth ground off, choose a face that is
hollow in its length, or, if none of the faces is hollow, then select a
face that is at a right angle to a good face of the file. It will be
noted that with one safe edge only the square file will require turning
over in order to operate upon both corners and maintain in each case a
safe edge of the file against the flat sides of the keyway. For this
reason many workmen select the two best parallel faces of the file and
grind off the two other faces, giving to the file two safe edges, one
opposite to the other. In this case either of the cutting faces of the
file may be used upon the whole end face of the keyway operating close
up to the corner, or if the file is much narrower than the keyway it may
be used with a side sweep that will prevent the file from pinning, and
produce much truer filing.
It is useless to attempt to cut out a square corner with a square file
unless one edge of the latter is ground safe, because the teeth of the
file itself do not form a square corner, and it is therefore only by
grinding the teeth off one side that the points of the file teeth can be
brought full up to a sharp angle. Here, however, it may be noted that
even if the filing is performed with the best of safe-edge files, and as
carefully as possible, it will still be necessary to square out the fine
corners with the edge of a fine smooth half-round file.
If the edges of the keyways are rounding, as they are sometimes made
where strength is required in the strap, it is better to take a file
nearly or about 1/8 inch larger in diameter than the width of the
keyway, and grind two safe edges on it, otherwise the round file is very
apt to go astray and cut the sides as well as the edge of the keyway.
An equaling file is much better for keyways than one actually parallel.
[Illustration: Fig. 2309.]
Another way employed to finish small keyways is by the aid of the tools
shown in Figs. 2309 and 2310, which are termed drifts, because they are
driven through with a hand hammer. That shown in Fig. 2309 is intended
for holes having but little depth and not requiring to be very true,
such, for instance, as those cut in the ends of keyways or bolts to
receive cotters; the thickness at A A is made greater than at B C to
give the cutting edge clearance.
The form shown in Fig. 2309 is for use by hand, the teeth being cut
diagonally instead of across, as at A A, to preserve the strength. This
end may also be attained by making the serrations round at the bottom,
as shown in the figure.
[Illustration: Fig. 2310.]
The slant of the teeth on one side of the drift should cross the slant
of the teeth on the diametrally opposite side, because if the teeth on
opposite sides were parallel one to the other the drift would have a
tendency to move over to one side, and crowd there during the process of
drifting.
In using these drifts the keyway should first be filed out to very
nearly the finished size, leaving very little duty for the drift to
perform, although the drift may be driven a short distance into the
keyway occasionally during the filing, so as to show where filing is
requisite. The work must lie flat and level upon a metal block, lead
being preferable, and oil freely supplied to the drift. "If the hole is
a deep one, and the cuttings clog in the teeth, or if the cut becomes
too great (which may be detected by the drift making but little
progress, or by the blows sounding solid) the drift must be driven out
again, the cuttings removed, and the surplus metal, if any, removed by
filing. The drift must again be freely oiled, and driven in as before,
and the operation continued until the drift is driven through the
keyway. After the drift has passed once through it should be reversed
(or, if a square one, turned a quarter revolution) and again driven
through, so that each side of the drift will have cut on each side of
the hole, which is done to correct any variation in the size of the
drift" ("Complete Practical Machinist").
The great desideratum in using these drifts is to drive them true, and
to strike fair blows, otherwise they will break. While the drift is
first used, it should be examined for straightness at almost every blow;
and if it requires drawing to one side, it should be done by altering
the direction in which the hammer travels, and not by tilting the hammer
face.
[Illustration: Fig. 2311.]
In Fig. 2311, suppose A to be a piece of wood and B and C drifts which
have entered the keyways out of plumb, as shown by the dotted lines D
and E. If, to right the drift C, it was struck by the hammer F in the
position shown, and travelling in the direction denoted by G, the drift
C would be almost sure to break; but if the drift B was struck by the
hammer H, as shown, and travelling in the direction denoted by I, it
would draw the drift B upright without breaking; or, in other words, the
hammer face should always strike the head of the drift level and true
with it, the drawing of the drift, if any is required, being done by the
direction in which the hammer travels. When it is desired to cut a very
smooth hole, two or more drifts should be used, each successive one
being a trifle larger in diameter than its predecessor. Drifts slight in
cross-section or slight in proportion to their lengths would be tempered
evenly all over to a blue, while those of stout proportions would be
tempered to a deep brown, bordering upon a bright purple.
For cutting out long narrow keyways, that are too narrow to admit of a
machine cutting tool, and for very true holes, not to be cut out in
quantities all of the same dimensions, it has no equal.
[Illustration: Fig. 2312.]
Hand drifts are sometimes used to cut keyways in small bores, as in
small hubs, the method being shown in Fig. 2312, in which A represents a
pulley with a keyway to be cut in the hub _b_; _c_ is a plug, and _d_
slips of iron placed between _c_ and the drift _e_ to press the latter
to its cut. It is obvious that in this case the keyway in the pulley
will be cut parallel, and the taper must be provided for in the key seat
in the shaft. Keyways cut in this way are more true than those filed
out. It is also obvious that the sides of the keyway, as well as its
depth, may be finished by a drift, and this is very desirable (on
account of insuring parallelism) when the key is to act as a feather
that is to have contact on the sides and not bind top and bottom.
The most improved form and method of using this class of tool, however,
is as follows:--If a keyway is to be cut out of solid metal, holes are
drilled as closely together as the length of the keyway will admit,
their diameter nearly equaling the required width of keyway, after these
holes are drilled through the metal remaining between them.
TEMPLATES.--Templates for vice work are used for two purposes: first to
serve as guides in filing work to shape and size, and secondly to test
the finished work. When used as guides to file the work they are mainly
used to work of irregular, curved, or angular form, to which the square
and other ordinary vice tools cannot be applied.
Fig. 2313 represents a template for filing out a square hole. The edges
A, B are at a right angle to each other, the wire simply serving as a
handle.
There are two methods of applying this template; the first is to file
out two opposite surfaces of the hole to the required diameter, making
them true and parallel one to the other, and to then employ the template
while filing out the remaining two sides; the other is to file out one
side and apply the template from that as a base for the other sides. The
first is preferable because the liability to error is a minimum.
When work is to be from a template, the latter obviously becomes the
original standard, and in many cases the best method of forming it so as
to insure correctness and enable its proper application to the work is a
matter of great consideration. The shape of the template must, of
course, be marked by lines which should be as fine and as deep as
possible. But it does not matter how closely the template may be filed
to these lines, it will still have some error, and this can in many
cases be discovered and corrected during its application to the work. In
the following examples there are principles which will be found of
general application:--
[Illustration: Fig. 2313.]
[Illustration: Fig. 2314.]
[Illustration: Fig. 2315.]
[Illustration: Fig. 2316.]
[Illustration: Fig. 2317.]
Let it be required to make or test a piece of work such as in Fig. 2314,
the teeth to be equally spaced, of the same angle, and of equal height.
A template must be made of one of the two forms shown in Fig. 2315. To
begin with, take a piece of sheet metal equal in width to at least two
teeth, and, assuming that the template is to have two teeth, file its
sides P Q, in Fig. 2316, parallel, and make the width equal to twice the
pitch of the teeth. We next divide its width into four equal parts by
lines, and mark the height, as shown in Fig. 2316. If we desire to make
the template such as at A, we cut out the shaded portion; or for the
template at B, the shaded portion. It will be observed, however, that in
template A there are two corners C and D to be filed out, while at B
there is but one E, the latter being the easier to make, since the
corners are the most difficult to file and keep true. The best method of
producing such a corner is to grind the teeth off the convex side and at
the edge of a half-round file, producing a sharper corner than the teeth
possess, while giving at the same time a safe edge on the rounded side
that will not cut one angle while the other is being filed. But when we
come to apply these templates to the work, we shall find that A is the
better of the two, because we can apply the square S, Fig. 2317, to the
outside of the template, and also to the edge F of the work, which
cannot be done to the edges G of the work and H of the template, because
the template edge overhangs. We can, however, apply a square S´ to the
other edge of B, but this is not so convenient unless the tops of the
teeth are level.
[Illustration: Fig. 2318.]
[Illustration: Fig. 2319.]
Assuming, therefore, that the template A is the one to be made, we
proceed to test its accuracy, bearing in mind that for this purpose the
same method is to be employed whatever shape the template may be.
Consequently, we make from the male template A, Fig. 2318, a female
template K, beginning at one end of K and filing it to fit A until the
edges of A and K are in line when tested by a straight-edge S. We then
move the template A one tooth to the right, and file another tooth in K,
and proceed in this way until a number of teeth have been made, applying
a square as at S, Fig. 2319, to see that the template A is kept upright
upon K. When K has been thus provided with several teeth that would fit
A in any position in which the latter may be placed, we must turn
template A around upon K to test the equality of the angles. Thus,
suppose at the first filing the edges _a_, _b_, _c_, _d_, upon A
accurately fit the template K, and the straight-edge shows the edges
fair; then if we simply turn the template A around, its angles, which
were before on the right, will now be on the left, as is shown at the
right of Fig. 2318. Thus in one position _a_ fits to _e_, in the other
it fits to _h_, or _b_ fits to _f_, and when turned around it fits to
_g_, and so on. Supposing that when thus turned around the angles do not
coincide, then half the error will be in the teeth of A and one-half in
those of K, and the best plan will be to correct them on A to the
necessary amount as near as judgment will dictate, and then to apply K
as before, continuing this process until A will fit anywhere in K, and
may be turned around without showing any error. But at each correction
the straight-edge must be applied, and finally should be tried to prove
if the teeth tops are level. We thus have two interchangeable templates,
of which A may be used on the work and K kept to correct A when the
latter becomes worn. It may be as well to add, however, that in first
applying A to K it is best to press the straight-edge S against the edge
of K, and hold it there, and then to place A against S, and slide it
down into K.
[Illustration: Fig. 2320.]
[Illustration: Fig. 2321.]
Fig. 2320 represents an example in which, the form being a curve, it
would be best to have the template touch more than two teeth, as shown
in the cut. By letting the side A, Fig. 2321, of the template T
terminate at the centre line of the two curves, and the end B terminate
at the top of a curve, turning the template around would cause end A to
envelop side C of the middle curve, thus increasing the scope of the
template. Suppose, however, that the base curve D required to be true
with the teeth, then a second template T´ must be used, its ends at E
and F measuring an equal length or height, so that when they are placed
even with the ends of the work, the distances G H being equal, the
corrugations will be true to the curve D D. Now let it be supposed that,
instead of making a template to test a piece of work such as in Fig.
2321, it is required to make a template for use in making another piece
of work that is to fit to piece W, then template T in Fig. 2321 will not
answer, because it is a female template, whereas a male one is required,
so that the edge of the template may coincide with that of the work. But
we may convert T, Fig. 2321, into a male template by simply cutting off
the edge A as far as the line J, and causing its right-hand edge to
coincide with the edge of the work so that the latter, after being
fitted to the template, may be turned upside down and fit upon the piece
of work.
[Illustration: Fig. 2322.]
[Illustration: Fig. 2323.]
[Illustration: Fig. 2324.]
In Fig. 2323 is an example in which the forms of both sides of a piece
require to be exactly alike, and the easiest method of accomplishing
this is as follows:--The face A should first be made true, and face B
made parallel to A. A centre line C may then be drawn, and from it the
lines E, E may be marked. The lines D are then drawn parallel to A A,
lines E being made square to D and to A. The sides E may be calipered to
width and parallelism, and all that will then remain is to file the
angles F, F and the ends G, G to their required lengths. For F, F all
that is necessary is a template formed as in Fig. 2324. The object of
dressing the ends G, G last is that if they were finished before, their
faces E would have to be made at exactly correct distances from them,
which would render the job considerably more difficult.
[Illustration: Fig. 2325.]
[Illustration: Fig. 2326.]
Fig. 2325 represents a sketch for a piece of work whose two sides are to
be shaped exactly alike, requiring a template of the form of the work,
as shown. From this a second template, Fig. 2326, is made, and to this
latter the work may be filed. To make the template in Fig. 2325, which
represents the work, the edge _x_ _x_ must be made straight, and the edge
D parallel to it at the proper height. A centre line S is then marked,
and the edges at E may be filed equidistant from S and square to D;
hence they will be parallel to each other. The side sections F should
then be filed equidistant from S and parallel to each other. They should
be the proper width apart and square to D, being tested in each of
these respects. The line joining E and F should be left full, as
denoted by the dotted line at A on the right. The edges at C, C should
then be filed, calipering them from the edge _x_ _x_. Edges G, G are
obviously equidistant from S and parallel to S, or, what is the same
thing, at a right angle to _x_ _x_, from which they may therefore be
tested with a square, and, finally, the edges B are made parallel to _x_
_x_, and the ends H made square to _x_ and equidistant from S. We have
now to file the angular groove at A, and to get this true after marking
its depth from the lines at A, we file it first to the lines as near as
may be by the eye and very nearly to the full depth. We then make a
small supplemental male template T, Fig. 2327, equal in width to the
distance E F, or, in other words, to the width of the step at A, and
having its edges quite parallel. Its end is then filed to fit the groove
at A, when its edge meets and coincides with edge E, as in Fig. 2327, T
representing the supplemental template. It is clear that when the
[V]-groove A is so filed that T will fit it with either of its edges
against E, the angles of the groove will be alike, and we may then make
a male gauge, as in Fig. 2326, that may be used to mark or line out the
work and to use as a template to file it to, its edge H being kept
parallel to face D, Fig. 2325, of the work.
[Illustration: Fig. 2327.]
CHAPTER XXVII.--VICE WORK--(_Continued_).
[Illustration: Fig. 2328.]
[Illustration: Fig. 2329.]
There are two principal kinds of connecting rods, first those in which
the brasses fit in spaces provided in the solid rod, and which are known
as solid-ended connecting rods, and second those in which the brasses
fit in a strap secured by bolts or keys to the end of the rod. In Fig.
2328 is shown the simplest form of solid-end connecting rod. It consists
of a rod enlarged at its end to receive a brass held up to the journal
by a set-screw as shown, one-half the bore being provided in the rod and
one-half in the brass. The objection to this kind of rod is that as the
bore wears the rod gets shorter and no means is provided to restore its
length, and that during the pulling stroke of the rod the whole of the
strain is concentrated on the end area of the set-screw, and this causes
it to imbed in the brass, giving play to the brass unless frequent
adjustment is made. It is, therefore, difficult to readily maintain a
very accurate adjustment of fit with a simple set-screw of this kind.
This may be to some extent remedied by the construction shown in Fig.
2329 in which the half brass A threads upon the stem of the rod, so that
when it wears shorter to the amount of half the pitch of the thread upon
the rod end, the brass may be unscrewed half a turn, and the original
length will be restored. The cap is held on by two screws, which may
have slotted heads as shown, or screws with check-nuts to prevent the
screws from slackening back, as all screws are apt to do that receive
alternating strains in reverse directions.
[Illustration: Fig. 2330.]
[Illustration: Fig. 2331.]
[Illustration: Fig. 2332.]
[Illustration: Fig. 2333.]
Yet another simple form of solid-end connecting rod is shown in Fig.
2330, there being two brasses with a key on one side and a set-screw on
the other. In this case, as soon as either brass is moved by the key it
can fit the rod at the top and at the bottom only; hence there is but
little to hold the brasses sideways in the rod, and furthermore the
brasses are damaged from the key and the set-screw acting directly upon
them, as will be explained with reference to strap-ended rods. In Fig.
2333 is shown a very substantial form of solid-ended rod, a sectional
view being shown in Fig. 2331. The bottom or back brass A has a flange,
as shown in Figs. 2331 and 2332 at A, which secures it to the rod end at
the back. The top or key brass B has the keyway partly sunk in it, and
the key binds against one side as well as on the bottom of the keyway,
and this draws that brass close down to the face of the rod, as shown in
Fig. 2331.
In this as in all other connecting rods in which one edge of the key
beds against the back of the brass, the taper for the key should be cut
in the rod so that the edge which meets the brass will stand square
across the opening for the brass; in this way the back of the brass will
also stand square across, which is easier to mark off and cut, plane,
and fit. If the taper for the key is cut on the brass, marking the
latter and fitting it become more difficult, as it must be put in and
out of its place to fit and bed the taper for the key edge, whereas, in
the other case, it can be squared with a square while planing and
fitting. As the bore of connecting-rod brasses wears, and the lost
motion incident thereto is taken up (by driving in the key) the location
of the brasses in the rod end is altered, making the rod longer or
shorter according to the location of the key. But when this wear has
been sufficient to let the key pass through the rod, slips of iron
termed liners are inserted between the backs or bedding faces of the
brasses and the end of the rod or crown of the strap, as the case may
be. In putting in these liners the location of the brasses in the rod
end may be adjusted so as to bring the brass back to its original
position and restore the rod to its proper length, and in doing so the
back brass, as distinguished from the key brass, is the one to be lined
first.
[Illustration: Fig. 2333.]
[Illustration: Fig. 2334.]
In the rod ends shown in Figs. 2333 and 2334 the joint faces (that is
the faces where the brasses meet) must be filed away to take up the
wear, hence the rods get shorter. In Fig. 2333 the liner may be placed
behind either brass, A or B, or behind both, the thickness of that
behind A adjusting the length of the rod (which is always measured from
centre to centre of the respective brass bores), while the thickness of
that placed behind B would simply act to prevent the key from passing so
far through the keyway. To prevent as far as possible the wear from
altering the length of the rod, the key at one end of the rod is placed
outside the crank pin or at the outer end of the rod, as in Fig. 2333,
while at the other end it is placed between the brasses and the stem of
the rod, as in Fig. 2334. In this latter case the thickness of liner
placed behind the key brass B (as the brass against which the key bears,
or the brass next to the key, is always termed) would adjust the length
of the rod, while the thickness of liner placed behind the back brass
(as the other brass is termed) would be the one to adjust the distance
the key would pass through the keyway.
[Illustration: Fig. 2335.]
In this form of rod end, as in many other solid-ended rods, the flange
or collar of the crank pin, if solid with the pin, requires to pass
through the opening in the rod end which receives the brasses. This may
be accomplished by making that opening large or wide enough to pass over
the crank-pin collar (which will increase the width of the brasses, and
hence that of the rod end); or else the crank-pin collar may have two
flat places filed on it, as in the end view shown in Fig. 2335. The
objection to this plan is that the rod can only be taken on and off in
one position of the engine; that is, when the two flat places A and B,
Fig. 2335, stand parallel with the length of the rod.
[Illustration: Fig. 2336.]
[Illustration: Fig. 2337.]
[Illustration: Fig. 2338.]
[Illustration: Fig. 2339.]
[Illustration: Fig. 2340.]
[Illustration: Fig. 2341.]
[Illustration: Fig. 2342.]
It will be noticed in Fig. 2331 that the brass B does not fill the space
in the rod. This is because that brass has to pass in over crank-pin
collar and push up into the journal after it is in the rod. To make this
space as small as possible, and to enable giving the crank pin as large
a collar as possible, the key brass is sometimes beveled off, as shown
in Fig. 2336 at A B. Another form of this rod end is shown in Fig. 2336,
in which there are two keys to the brasses, the object being to adjust
the keys to maintain the rod of its proper length. In order to
facilitate making this adjustment, there should always be upon the face
of the rod end centrepunch marks, as shown in Fig. 2338 at F and G, or
else two deep marks, as shown at C D in Fig. 2337. Then, in lining up
the brasses to set the key back, the rod may be restored to its original
length by putting behind the back brass a piece of metal of such
thickness as will bring the centre of the bore of the back brass B even
with the centrepunch or other marks. This being the case, it does not
matter about the exact thickness of the piece of metal put behind the
other brass, since a variation in that will only act to let the key come
more or less through the rod end without affecting the length of the
rod. In Fig. 2337 is shown a form of rod end sometimes used. The end
being open, the brasses pass through it. In this case the whole strain
of the pull of the rod falls upon the edge of the gib at top and bottom
of the strap, causing the gib to wear out very fast; furthermore, the
back brass condenses the metal at the back of the brass opening, acting
to pene it and throw the points of the rod end open, which it always
does, the jaws of the gib imbedding in the jaws of the rod. This opening
of the rod jaws makes the brasses loose in their places; hence this is a
weak and undesirable form of rod end, though very convenient to take on
and off. In Figs. 2338, 2339, 2340, and 2341 is shown a form of
solid-ended rod of more modern construction. In this case a wedge A is
used instead of a key, being adjusted by screws passing through the rod
at the top and bottom, it being obvious that the set-screws may have
check-nuts added. B is the back brass, and C the key brass. In this case
the flange of the brass goes next to the crank pin, and a plate D is
provided to serve as a flange on the front face of the brass. In Fig.
2338 this plate is removed to show the wedge A; but it is shown in the
plan view, 2339, and the end view, 2340, and by itself in Fig. 2341. A
groove is cut on each side of the two brasses and the plate spans the
brasses, passing up the groove being held in position by a screw at E.
The opening for the brass (in the rod end) is here shown wide enough for
the rod end to pass over the collar of the crank pin, but in many cases,
with this as well as with other forms of solid-ended rods, the crank pin
may be made plain--that is, without a flange--and have a washer secured
by a screw, so that by removing the washer the rod may be put on with
the brasses already in place, and made no thicker (at the joint face)
than is necessary for strength. In Fig. 2342 is shown what may be termed
a clip-end connecting rod, the screw closing the rod end (to take up the
wear) against the spring of the metal. It is obvious that in this case
the hole may receive a brass bush split as is the rod end and secured
from turning by a pin. Fig. 2343 presents another form of solid-end rod,
which admits of the use of a brass having a flange on both sides of the
strap, and will take on and off by removing the cap B. If the crank-pin
collar is solid, the brasses must be placed on the crank pin, and the
rod, with the wedge in place, lifted or lowered to the brasses; but if
the crank pin has a washer and bolt, the rod may be put together and
slipped on its place.
A compromise between the solid and the strap-rod end is shown in Fig.
2344, which represents a design used upon the fast engines of the
Pennsylvania Railway. The piece A takes out to enable putting on the
rod or taking it off, A being secured in position by the bolt and nuts
shown. This forms a solid and durable rod that is much less costly to
make than strap-ended rods.
[Illustration: Fig. 2343.]
[Illustration: Fig. 2344.]
[Illustration: Fig. 2345.]
[Illustration: Fig. 2346.]
[Illustration: Fig. 2347.]
[Illustration: Fig. 2348.]
The simplest form of strap-ended connecting rod is that shown in Fig.
2345; S is the strap, secured to the rod end by the key D and gib C. A
is the top, and B the bottom, or crown brass, and E the set-screw for
securing the key in its place. [When the rod ends are forged in separate
pieces, to be afterwards welded to the stem of the rod after the strap
brasses are fitted up (which is done for convenience in handling them
while fitting them up), they are termed stub ends.] This form of rod
affords great facility for connection with the journals as the strap is
easily removed. As the strap, however, is only secured to the rod by the
gib and key, and as these have a small amount of area on the sides, it
is not unusual to employ two gibs and one key, as in Fig. 2346, which
holds the strap more securely, and more effectually prevents its
movement sideways upon the rod end. In rods in which gibs and keys alone
are used to hold the strap to the rod, the strap moves along the rod as
the key passes farther through the strap, and the fit of the strap to
the rod must be easy enough to permit of this motion; hence it cannot be
locked to the rod. This, however, may be done by the employment of a
bolt as well as a gib and key, as is shown in Fig. 2347. The edge of the
gib here abuts against the back of the top brass, or key brass, as it is
sometimes termed, which is objectionable, inasmuch as that it is apt to
indent the brass, as shown in Fig. 2348 at B. This causes the bore to
close at A, and causes the journal to heat, while it makes the brass fit
loosely between the jaws of the strap, because it stretches the metal at
the back of the brass, which has the same effect as pening it with the
hammer.
In Fig. 2349 is shown an end of a connecting rod, such as is employed on
American locomotives, the use of a gib being dispensed with, and the
strap being held by two bolts. To prevent the edge of the key from
imbedding in the brass, a piece of hardened steel is sometimes placed
between the key and the brass, as shown in the figure.
In some designs this method is reversed, the gib being prolonged in a
screw-thread, as shown in Fig. 2350, and the key head is carried over as
shown. Two wing nuts are provided for adjusting the key, which enables
its adjustment without the employment of a wrench or hammer.
To prevent the end of the set-screw from raising a burr on the key,
which would prevent its easy motion through the keyway, a shallow groove
is sometimes cut along the key, as in Fig. 2351 at A, the end of the
set-screw binding on the bottom of that groove.
In other forms of rod a gib and key are used as well as two bolts. This
not only holds the strap very firmly, but it prevents to a certain
extent the pening of the back of the brass, explained with reference to
Fig. 2348. It is obvious that in the absence of a gib the key moving
under friction against the brass stretches the metal more than a gib
that presses against the brass, but has no motion endways.
[Illustration: Fig. 2350.]
[Illustration: Fig. 2351.]
[Illustration: Fig. 2352.]
In Fig. 2352 the strap is held by bolts having nuts at each end, instead
of a solid head at one end and nuts at the other. The single nuts at the
top serve to draw the bolts out when the rod is to be taken apart, thus
saving the use of the hammer for that purpose.
[Illustration: Fig. 2353.]
In Fig. 2353 is shown a form of rod in which the strap is held by two
dies A B, and a bolt which passes through the strap, the dies, and the
rod end.
[Illustration: Fig. 2354.]
In Fig. 2354 is a form of rod end in which the strap ends are keyed
against abutments on the rod by means of the key A. The abutments and
strap ends being bevelled, keying up the strap with A closes it down
upon the rod.
[Illustration: Fig. 2355.]
In Fig. 2355 is a form of rod end largely used upon marine engine work;
A is the end of the rod, B, B the brasses, and D, D bolts passing
through the brasses. Here we have no means of correcting the alteration
of length due to the wear, unless a line is marked on the rod end, as at
C, and the distance that line should stand from the centre of the brass
bore is marked beside it, as is denoted by the figure in the cut,
indicating that the line should stand 9 inches from the cuts of the
brass bore.
In general practice the inside jaw faces of connecting rod straps and
the faces of the rod are made parallel, which serves very well when the
duty and wear is not great; but when the wear and tear is great, as in
locomotive work, it is much better to make them taper; indeed, they are
in any event better taper, because in that case the brasses can be made
a tighter fit. The reason for making them parallel is because they can
be more readily planed so than taper; but a parallel strap is more
difficult to fit, and cannot be made so good a fit as a taper one, even
when new, while it is very much more difficult and expensive to repair.
[Illustration: Fig. 2356.]
When the faces of the stub end (or, more properly speaking, of the
block) are parallel one to the other, and the inside faces of the strap
are also parallel, the strap must be made a very easy fit to the block,
in order to be an equal fit from end to end; for if the strap fits as
tightly as it should to be a good job, it will, when put on the rod,
spring open, fitting across A, Fig. 2356, only; this because the strap
springs open from contact at A. The fit, then, can only be such as will
not have force enough to spring the strap open, and this is very small
indeed even in a very strong strap. It is within the mark to state that
in a strap measuring 4 inches between jaws, at A in Fig. 2356, it can be
forced by hand on the rod sufficiently tight to spring them open 1/16th
of an inch at B, B. When the brasses are fitted into the strap a second
difficulty arises, inasmuch as they must be made a very easy fit, or
else they will spring the strap open so that it will neither fit at A
nor at B, whereas it is desirable that the bottom brass drive home, and
the top brass, or one nearest the rod, just push home by hand.
When the rod requires repairing a more serious difficulty arises.
Suppose, for example, that the strap requires refitting to the rod, then
it must evidently be closed between the jaws, especially if the rod end
requires filing up, as it usually does. Now the jaws being parallel
cannot be closed without being taken to the blacksmith shop and closed
across the crown, as at A in Fig. 2357; for if the jaws are closed (as
they might be) by pening the corners B, C the jaws would close as
denoted by the dotted lines. The brasses will have to be made larger
than the diameter at D, in order to fill the space at A, and will be an
easier fit as they pass from D to A, whereas the opposite should be the
case. The strap must therefore be closed across A in the blacksmith's
fire; this will scale the crown end and render it necessary to file down
the whole of the surface on each of the side faces of the strap and rod
in order to make them parallel, as they must be to have the flanges of
the brasses fit when home in the strap.
[Illustration: Fig. 2357.]
The blacksmithing will in most cases render it necessary to file out the
keyways, and this again entails the making of a new gib and key. All
this extra work may be avoided by making the block and strap a little
taper. But before proving this it may be noted that when the rod is made
parallel the strap may be made to fit tightly by making the jaws taper,
as shown by dotted lines in Fig. 2357; so that when the strap is on the
rod, and the jaws spring open by reason of the close fit, the fitting
surfaces will be parallel. Such a construction would be faulty however,
for the brasses would fit too tight when entering the strap, and get
easier as they passed to their places, whereas, as already stated, the
exact opposite should be the case.
[Illustration: Fig. 2358.]
Let us now observe the advantages of a strap, whose inside faces are
made as in Fig. 2358; smaller at A than at B, and also at C than at D,
while the thickness from A to B is greater than that from C to D, while
the widths C D are less than the corresponding width of the rod.
First, as to fitting the strap to the rod. It may be made so tight to
the rod that it will only just pass on when pushed by the hand.
Second, this will render possible a tighter fit than would be possible
with a parallel strap and rod.
Third, the width B A being taper, the brasses may be easier made a good
fit, because there will be some metal to fit on after they enter at B.
Fourth, the brasses may be made a tighter fit, the bottom brass being
tight enough to spring the strap a trifle, easing but not destroying its
fit on the rod.
Fifth, the top brass may be made a handsliding fit to the strap without
springing the strap open, which being already under a tension because of
the spring due to the bottom brass, will be more rigid and permit of a
tighter degree of top brass fit, without springing open and away from
the rod.
Sixth, this will leave the bottom brass a tight driving fit, and the top
a hand sliding fit, which is desirable, because the top brass has to be
taken out to get the rod off while the bottom brass remains in its
place.
[Illustration: Fig. 2359.]
Seventh, what is of more consequence than all, the strap can be more
easily and cheaply refitted to repair it. Thus, in Fig. 2359, suppose
the strap to have been closed by pening at D; then whether the end D
will be narrowed will depend on the amount the strap was closed, and the
amount of taper it had before closing. Let us take, however, the most
unfavorable conditions, and suppose that the amount of taper was so
small, and the amount of closing by pening so great, that the jaws were
made taper and smallest at D. Then the amount to be filed off to bring
the width of jaw correct, and a fit to the strap, will be less than if
the strap jaws were formed as in Fig. 2357, as will be seen by comparing
Fig. 2357 with Fig. 2359, the amount to be filed away being that between
the dotted and the full lines in both figures; the amount of closure
being the same in the two figures.
But there is another great advantage, inasmuch as in pening, the strap
may be pened and tried on the rod, the strap being pened and tried
alternately until the required fit is obtained, which is not practicable
with upsetting in the blacksmith's shop.
Again, the keyways in the strap will not be set out of true with those
in the rod, as they are apt to be when upsetting is resorted to, nor
will the strap be scaled; hence the side faces will require but little
filing.
Furthermore the step may be located so as to come against the rod end
when the wear has let the key down, and this will prevent the strap from
passing too far upon the rod, and, therefore, tend to prevent the rod
length from being improperly altered from errors in the thickness of the
liners placed behind the brasses to take up the wear.
FITTING UP CONNECTING RODS.--The method of fitting up a connecting rod
depends entirely upon its size. Very small rods to be made in numbers
are usually got out by means of special devices which leave the fitter
but little to do; indeed, sometimes the machine work is so accurately
and finely fitted and finished as to finish the rod without the aid of
the vice hand, save to put it into its place upon the engine or machine.
As, however, the dimensions of the rod increase, this method of
manipulation is in practice departed from, and the filing, fitting, and
adjusting operations increase. In any event, however, the principles to
be observed in the manipulation are the same, because the points to be
observed in the fitting by hand work must be accomplished by the machine
if the rods are to be finished by machine work.
Let Fig. 2360 represent a connecting rod; A representing the centre line
in the side, and F the centre line in the edge view, and it is obvious
that the axial lines, B and C, of the brass bores must stand at a right
angle to line F, and be parallel to each other, because the journals on
which they fit will do so. Furthermore, the faces of the brasses, as E,
must stand their proper distance from the centre line F, this distance
being at each end respectively half the whole width D, and the faces E
must be in the same plane whatever their widths may be. The centre lines
A and F are imaginary lines not worked to (except it be in marking or
lining the rod out for the planing operations); but the method employed
to fit up the rod must be such as will make all parts true to those
lines if they were tested by them.
The process of fitting up a connecting rod may be tersely stated as
follows: 1st, the rod is planed; 2nd, the straps are planed; 3rd, the
straps are fitted to the rods; 4th, the straps are drilled and bolted to
the rod; 5th, the keyways are cut, and the keys and gibs fitted; 6th,
the side faces of the rod ends are again planed with the straps on; 7th,
the brasses are fitted and the rods marked off for length and the
brasses bored; and, 8th, the file finishing and polishing done.
[Illustration: Fig. 2360.]
[Illustration: Fig. 2361.]
[Illustration: Fig. 2362.]
[Illustration: Fig. 2363.]
[Illustration: Fig. 2364.]
In the case of very large rods the two ends are made and fitted up as
separate pieces, and are afterwards welded to the body or stem of the
rod, and the setting of the ends true one to the other after the welding
affords such an excellent insight into the alignment of rods that it may
be well to describe it. First, then, the rod being laid on its side, two
straight-edges, or rather winding strips, S and S´, Fig. 2361, are
placed on the side faces, and the rod will be set in this direction when
their ends A, B, C, D, appear parallel when sighted by the eye. If the
winding strips are adjusted to stand straight across the rod, and,
therefore, parallel one to the other, any twist or wind in the two rod
faces will be very plainly discernible by the sighting process. The rod
is then stood on edge, as in Fig. 2362, to test the alignment of the
side faces. A straight-edge S is pressed firmly against one of the
faces, as H in the figure, with the other end elevated as shown. The
elevated end is then lowered, the motion serving to keep the end fairly
bedded against face H. The distance, I J, Fig. 2363, is then measured.
The straight-edge is then used in the same manner on the other side of
the rod as at S in the figure, and the distance K L is measured, the
setting in this direction being correct when distances I J and J K are
equal. The straight-edge is then applied to the edge faces of end H of
the rod, as in Fig. 2364, at M and at N, the distances O, P, are made
equal. During these operations a straight-edge is applied along the body
of the rod to see where to set it to effect any required adjustment, and
if that body is straight the adjustment is made near the end at which
the straight-edge is pressed to the rod.
The setting of the small end I is effected in the same manner, but the
straight-edge will in this case fall over the face at the larger end, as
is shown in Fig. 2365; hence, instead of measuring, lines as G and T are
marked coincident with the edge of the straight-edge and the distances
T U, I G, are made equal. Winding strips are applied to the edge faces
as well as to the side faces, and as making one adjustment or alignment
may alter another, the whole process must be repeated until the whole of
the tests prove the setting to be true.
[Illustration: Fig. 2365.]
[Illustration: Fig. 2366.]
[Illustration: Fig. 2367.]
[Illustration: Fig. 2368.]
Now suppose the rod to have been forged solid and all these faces to
have been made true in the planing, and the first operation is to fit
the straps to the rod ends. The strap should be put in place on the rod
and moved laterally, when the centre of its motion where it moves the
least will be the place where it binds and therefore requires filing. If
its side faces come atwist with the side faces of the rod end, as shown
in section in Fig. 2366, either the faces of the rod end or the inside
faces of the jaw are out of square as denoted by the dotted lines. In
any event the face E, Fig. 2367, of the rod end should be surfaced true
and made at a right angle to the side face, and if to be made parallel
to M, also at a right angle to K, a square and a surface plate are used
to test them. If the diameter J is to be smaller than that at H, then
the angle of both face E, and its opposite, should be equal with
reference to K. These faces should be finished by draw-filing, with the
file marks lengthwise of the rod. To fit the strap, proceed as follows:
To find where it requires filing, place it on the rod (having previously
put red marking on the rod end), and move it endwise and sideways,
observing where the least motion takes place when the strap is moved
sideways by pressing its crown end, for this point of least motion is
always where it fits the tightest. To test the jaw faces for being
square apply a straight-edge S, and a square P, Fig. 2368, pressing S
against the strap, and P firmly against S.
[Illustration: Fig. 2369.]
When the strap shows to bed well on the rod and its motion is an ambling
one (and not a pivoted one), it fits properly, and if both rod and strap
have been filed square, their side faces will come fair or even. The
keyways being drilled, may then if necessary be filed out, for which
purpose it is necessary to bolt the strap to the rod, a process that
requires very skilful treatment, because if the tightening of the bolts
moves the strap on the rod, or if the strap be moved on the rod after
the clamp is tightened, the keyways will not come fair when the clamp is
taken off. In Fig. 2369 the strap is shown held to the rod by plates C
and bolts B, the rod being shown in position ready to file out the
keyway. It is better, however, to let the side face of the rod stand
vertical as the strap will stand steadier that way. The strap should be
set fair with the outside faces, which will bring the keyway fair if it
is properly located. The bolt nuts should be tightened gradually, first
one a little and then another, going over all four once or twice before
they are fully tightened, and if the strap is not fair when they are all
tight, all must be loosened before the strap is adjusted, or the clamp
pressure will cause the strap jaws to spring out of true, and the
keyways will not come fair when the clamp is removed.
Should the keyways not come fair when the strap sets fair on the rod the
strap may be set to accommodate the keyways, and thus save filing, but
this must be done before clamping it to the rod end. Care must, however,
be taken to see if cutting the strap out to suit the keyway may not
leave too little metal on one side of the keyway when the strap is
subsequently planed.
The sides of the keyway should be filed true to a surface plate, using a
well-bellied file and as stout a one as possible, so that it may not
bend under the pressure, and file away the edges of the keyway.
The keyway should be made parallel to the side face of the strap, so
that it may be fair with the centre line F in Fig. 2360. It should be
made of equal width throughout, a piece of iron being used as a gauge in
place of the key, and this same piece of sheet iron will serve as a
gauge to plane the keys to thickness.
The corners of the keyway, if to be made square, should be filed out
with the corner of a smooth half-round file, because the corners even of
safe-edge files do not come up sharp enough.
For filing out the end faces of rectangular keyways, a square file with
both edges safe must be used, the safe edges being on opposite sides of
the file. For roughing out, a taper square, but for finishing, a
parallel, or equalizing file is preferable.
The next operation is to fit the keys and gibs. The key should first be
fitted and should be filed true to a surface plate, for in no other way
can a really good reliable gib be obtained, no matter how well the keys
may have been planed or milled. It should be filed a tight fit to the
keyway so that it may be used (with a light coat of red marking) to show
tight places in the keyway, driving the key in for that purpose from
first one and then the other end of the keyway. If, however, it is
driven too forcibly, it may seize or cut, and it will be difficult to
get it out, besides damaging both it and the keyway. When the keys are
reduced so that they will drive lightly into the keyway, they should be
tried in the rod and in the strap separately, moving the key laterally
or edgeways, so that it may mark any high places in the keyway of either
of them.
The finished key and gib should be left tight enough, that they will
hold themselves in any position in the keyway of the strap or of the rod
when standing vertical.
[Illustration: Fig. 2370.]
The head of the gib should be chamfered as in Fig. 2370, so that it may
be driven in and out to fit without raising burrs which would prevent it
from passing into the keyway, and the key should be similarly chamfered
and rounded in its width.
[Illustration: Fig. 2371.]
The width of the key and gib should be such as to just fill the key
ways, leaving no draw when the key is down in the keyway so that its
head is level with the head of the gib, as in Fig. 2371, A equaling the
keyway width; and their edges should bed fairly one against the other,
and against the edges of the keyway. The strap must then be keyed upon
the rod, and the side faces of the rod and strap planed to thickness,
placing a bolt and nut in the rod end in place of the brasses, so that
the key may lock the strap and bind it in position. The rod end should
be planed to thickness for the brasses and of equal thickness on each
side of the keyway. The brasses should be planed after the rod end is
planed to thickness. The width for the brasses should be measured while
the strap is on the rod end, because the width between the jaws of the
strap is greater when the strap is in place on the rod end than when it
is off, because in order to make the strap jaws a tight fit to the rod
end it is made narrower between the jaws than the width of the rod end,
so that the jaws spring open when the strap is pushed on the rod end.
The sizes for the brasses to be planed to will then be the width of the
strap across its edge face, and the width of the strap between the jaws
_when it is on the rod_; and for these sizes a wire gauge should be
made; or an adjustable gauge may of course be set.
The method to be pursued in planing the brasses is an important
consideration. It is most convenient to plane both the brasses together,
by which means much time is saved. To obtain this end the brasses are
sometimes cast together, as in Fig. 2372, and after planing and before
boring are cut in two at the narrow section A. In this case the brasses
are cast sufficiently wide from crown to crown as denoted by B to allow
for the length cut away in separating them. In other practice the joint
faces of the brasses are faced first and then soldered together for the
planing; but very large brasses are planed separately. In either case
the joint face of the brass should be made at a right angle to the faces
of the brass that fit the strap.
[Illustration: Fig. 2372.]
The brasses should be fitted separately to the strap, and hence should,
if joined, be separated, being cut in two in a shaper, if of the form
shown in Fig. 2372, and split by driving a keen chisel between the
corners of the joint faces, if the latter have been soldered. The back
or crown brass, and not the key brass, should be fitted first. The
corners of the ways, in the brass, for the strap should be eased just
clear with the edge of a smooth half-round file, because otherwise they
will rub down the sharp edges of the strap, and make the strap jaws
appear to be a bad fit when on the rod. The brass should be driven in
and out of the strap to fit, using a block of wood to strike on,
otherwise the skin of the bore may become pened, and when the brasses
are bored they will close in at the sides and become loose in the strap.
[Illustration: Fig. 2373.]
As a guide when fitting the bottom brass in the strap, place the strap
on the rod as in Fig. 2373, and take the measure of the strap at A A,
the strap overlapping the rod to admit the calipers or gauge. Each time
the brass is driven in the strap to try the fit, the calipers so set
should be tried in the strap (the brass being in the strap), as in the
figure, and when the calipers very nearly touch the strap jaws, the
strap with the back brass still in should be tried on the rod end, or in
the case of a very heavy strap the caliper measurement minutely taken
may be relied on to show that the brass does not spring the strap jaws
too wide open. It is better, however, to leave the brasses a little too
tight in the strap as they close slightly in the boring, becoming easier
in the strap.
[Illustration: Fig. 2374.]
[Illustration: Fig. 2375.]
After the brass has been tried in the strap, and before it is filed
again, it should be tried with a square, using a straight-edge also if
the square back is too short to cross both faces of the brass. The
method of testing is shown in Fig. 2374, in which B represents the
brass, S the square, and T the straight-edge. The inside face of the
flange should also be tried as in Fig. 2375, in which P represents the
surface plate, S the square, and B the brass. This will insure that the
brass face joint is square as it should be, and is further necessary
because the bearing marks on the brass are not to be altogether relied
upon.
[Illustration: Fig. 2376.]
In Fig. 2376, for example, the brass is shown in section in the strap,
and the side A of the brass has a bearing against the jaw B of the
strap, and hence would show marks of contact. The succeeding blows in
driving the brass, however, may cause the brass to have contact on the
side C with the jaw D; hence the bearing marks would show the brass to
fit well when such was not the case. This may be detected by striking
the brass on its joint face, and then measuring from E and from F to the
end of the strap, and then striking the joint face at F and again
measuring both distances, when any canting of the brass will readily be
detected. It is better, however, to also apply the square, as shown in
Figs. 2374 and 2375, because by this means the joint faces E F being
parallel to the crown face G of the brass, the brass will be fitted so
that when G meets the crown face H of the strap, the two will be
parallel to each other and require but little filing to fit or bed
together.
The crown of the brass should be bedded very finely to the strap, or it
will spring the strap jaws away from the rod when the key is driven
home.
Suppose, for example, that the crown of the brass did not bed well at A
in Fig. 2377, then keying up the strap would spring its jaws away from
the rod end, as shown at B C, the least error in the bedding having this
effect notwithstanding the fit of the gib jaws.
[Illustration: Fig. 2377.]
The second brass must be made to just fit the strap when the back brass
is in its place, and is small enough when the calipers, set as shown in
Fig. 2373, and tried as shown in Fig. 2376, just fit the strap. This
will insure that both brasses fit the strap when it is in its place on
the rod.
When both pairs of brasses have been fitted to their straps, the latter
should (if held by bolts) be bolted to their places on the rod, and the
centre of the respective spaces for the brasses will be the location for
the marks G, G, Fig. 2360. A pair of trammels should, however, be set to
the proper length of the rod and these marks tested. If the strap is
held by gibs and keys, as in the small end in Fig. 2360, the strap
should be put on its place with the gibs in, and drawn up the rod by
slowly forcing the key in until the mark G at that end stands in its
proper distance from G at the other end, at which time the key should
come through its proper distance.
The thickness of the brasses must be measured from these marks G, G to
the crowns of the straps and the ends of the rod respectively. If the
rod is of its proper length and the straps are in their proper
positions, these marks will come in the centre of the space for the
brasses. If, however, there is any error, as there is apt sometimes to
be in very large rods, the course to be pursued depends upon the kind of
rod end. If both straps are bolted to the rod end, the error may be
divided equally at each end. If one end has a key and gib or gibs, but
no bolt, as at the small end in Fig. 2360, the key brass may be made of
such thickness as to butt against the end of the rod and meet the mark
G.
[Illustration: Fig. 2378.]
For the large end, the thickness of the key brass, or, in other words,
the distance D in Fig. 2378, must be taken after the face of the crown
brass has been squared up, as described with reference to Figs. 2374 and
2375, the connecting rod strap being placed in such position that the
key will be up in its proper place.
When the joint faces of brasses do not meet, but are left open to take
up the wear, it is a difficult matter to properly adjust the brass bore
to the journal. If the flanges of the brasses do not quite fit the
length of the journal, as is very commonly the case, it is customary to
tighten the key until the rod end can just be moved by hand so as to
force the brass flanges against first one and then the other end of the
journal. This is an approximate adjustment; and if the journal heats at
all, the key is slacked back a trifle; whereas if it pounds, the key is
set up a little. As a matter of fact, then, nothing is actually known of
the precise fit of the brass to the journal; and while looseness may be
detected by the pounding, the brass may be tight enough to cause undue
wear without very sensibly heating the journal, especially if the latter
is freely lubricated. If, however, the brasses fit the length of the
journal, and do not butt, it is usual to drive the key in till the
brasses bind the journal, and to then slack the key back to the
necessary amount. What that amount should be cannot be stated, because
it varies with the taper of the key and the force with which it is
driven home. As a result, then, the operation is left to the judgment,
or, in other words, to guess-work, of men, many of whom are not well
experienced in the operation; while under any circumstances the actual
fit is not positively known. A plan not infrequently adopted is to
insert a piece of lead wire of small diameter between the brasses, the
key is first driven tightly home, and then slacked back until the lead
wire is just freed. It is estimated that the adjustment will then be
correct; there is no actual certainty of the fit, however, even in this
case.
Another objection is that the oil is apt to flow out of the opening, and
the brass having communication with the oil cup is better lubricated
than the other brass.
In cases where the brasses are difficult to get out of the strap,
because of the location or of the size and weight of the parts, a piece
of sheet brass is sometimes placed between the joint faces, and this
piece is filed thinner to let the brasses together, the necessary
thickness for the piece being ascertained by the lead wire process
described. If the strap is held to the rod end by a gib and key only,
and the joint faces are left open, there is nothing to lock the strap to
the rod end save the jaws of the gib, whereas when the brasses butt, the
key binds the brasses to the end face of the rod and the strap to the
brasses, which if there is any wear sideways (as in locomotives),
prevents the keys from wearing the sides of the key ways and the brass
flanges from wearing the straps.
A method of overcoming this defect is shown in Fig. 2379, where the
joint faces are left open, and four set-screws S, S, two on each side of
the rod, pass through the flange of one brass and abut against the face
of the other, serving to adjust the fit of the brasses to the journal,
and lock them in their adjusted position, locking at the same time the
brasses to the strap and the strap to the rod end.
When the rods are finished so far as the fitting of its various parts
are concerned, the brasses should be marked so that the bore, when bored
out, will leave an equal thickness of metal between the brass and the
strap on each side of the bore, while the rod will be of proper length.
To accomplish this, mark on the outside face of the top brass two lines
level with the faces which fit against the inside jaws of the strap, as
shown in Fig. 2380, A, B being the lines referred to. We then key up the
brasses in their places in the rod and fasten a centre piece in the
brasses at each end of the rod. Upon these centre pieces we first mark a
line parallel with and central between the lines A, B, and then a line
across the joint of the brasses if the joint faces meet, and in the
centre of the space between them if they do not meet.
[Illustration: Fig. 2379.]
[Illustration: Fig. 2380.]
Before applying the trammels to test the rod length, the latter should
be stood or placed in the position in which it works when on the engine;
for all rods deflect by their weight, the amount of such deflection
depending upon the position in which the rod is suspended. The trammels
also deflect, it is true, but their deflection is allowed for in setting
them, whereas the deflection of the rod will not be accounted for unless
it is trammelled when standing or lying in the position in which it
works.
FITTING UP SOLID-ENDED CONNECTING RODS.--In fitting up solid-ended rods
the side faces require to be filed up first and the jaws to receive the
brasses next, taking care to file them out either square with the faces,
or if slightly taper, as they should be, then each inside face should be
an equal degree of taper to the side faces. This is necessary so that if
the brasses are bored true to their own faces, the bore of the brasses
at one end of the rod shall stand parallel to the bore of those at the
other end.
The fitting of the keys and brasses is performed as described for
strap-ended rods.
The reason that the jaws or box that receives the brasses is but a
trifle taper is that in that case they are easier made a good fit, as
they can be tried in their places while being fitted and before being
reduced to the finished size, and furthermore because they can be put in
and taken out easier.
FITTING UP A FORK-END CONNECTING ROD.--A fork-end connecting rod affords
as good an example of vice work as can be found, because any faulty
workmanship, either in the individual truth of the parts, or their
relative truth one part to another, will make itself very plainly
apparent.
[Illustration: Fig. 2381.]
[Illustration: Fig. 2382.]
Fig. 2381 represents a side and plan view of an ordinary form of
fork-end rod, and the requirements are that the centre line A of the
brass bores at the fork end shall be parallel with the centre line B of
the bore at the butt end; that the side faces of all the brasses shall
be parallel one to the other; that the side faces at the fork end shall
be equidistant, or at the required distance, from the side faces at the
butt end as denoted by C, D; that the bores of the brasses shall be at
the proper distance apart to make the length of the rod come right; that
the brasses at the fork end shall be the right distance apart, and that
they shall stand parallel to each other, as well as to the bore at the
butt end, as denoted by the line E in Fig. 2382.
If the rod were of a size that it could be conveniently handled and
planed, if forged solid, the fitting up would be much simplified,
because the setting of the rod for the machine operation would, to a
great extent, insure truth in the relative alignment of the parts. Thus
all the side faces of the rod ends could be planed at one chucking, in
which case they would necessarily be parallel, and their proper relative
distances apart, if the rod was properly marked out by lines and planed
to the lines. The jaws or ways to receive the brasses would be slotted
out together, and necessarily true, if the rod was chucked true on the
machine table. But even in this case the rod has to be marked out by
lines denoting where the metal is to be cut off to, and the principles
involved in the lining are just the same as those involved in the
fitting up.
[Illustration: Fig. 2383.]
[Illustration: Fig. 2384.]
If the rod be large, the ends may be, and usually are, forged and fitted
up separately, and subsequently welded to the body of the rod, which has
been forged separately. In this case, the alignment of the parts is a
part of the process in welding the rod, and setting it after welding.
All the principles involved in making the rod ends separate, and
afterwards welding them, or in marking out a small and complete forged
rod, are, however, involved in the process of refitting an old rod in
the jaws, and putting in new brasses; hence a description of that
process will cover the whole ground. The first thing to do is to file up
the side faces, as F, G, Fig. 2381, and, in doing this, all that is
necessary is to file F up true, when tested by a straight-edge applied
as in Fig. 2383, in which R is the fork and S a straight-edge, whose
edge should measure the same distance at H as it does at I from the side
face F, while the face C measures the same distance from face A of the
other fork end, or from the imaginary centre line X, Fig. 2381. Then
turning the rod on its side, a straight-edge should be placed across the
face F, and one across the face G, as in Fig. 2384, at S and S´; and the
edges of the two straight-edges should stand parallel, when sighted in
such a position that the edges are very nearly in line with the eye, as
shown in the figure.
The inside faces of the fork jaws may be filed to measurement from the
outside ones.
[Illustration: Fig. 2385.]
[Illustration: Fig. 2386.]
[Illustration: Fig. 2387.]
The ways for the brasses should be filed square with the outside faces,
as shown in Fig. 2385, in which S is a [T]-square; but if one jaw is
wider than the other, as sometimes occurs, it will not matter, providing
that, with the square applied, resting against the side and the face of
the ways on the narrow jaw, the ways of the other jaw are equidistant
from the square blade, as would be the case; for example, if the width
of the ways of the jaw J extended to the dotted lines at K, L, because
the line P would still form the centre line of both jaws, standing at a
right angle to the side faces of the fork end, and parallel to the bore
of the brasses at the butt end. Before filing up the side faces at the
butt end, the strap should be fitted on and keyed up, so that its side
faces may be filed up with those on the rod. To test the truth of the
side faces at the butt end, a straight-edge should be applied, as at S
and S´´, Fig. 2386, being pressed firmly to the side faces at the butt
B, the fork faces being measured from the edge of the straight-edge at
that end, and also with straight-edges, as in Fig. 2384. The brasses,
after being fitted into the ways of the jaws, should have their joint
faces squared, as in Fig. 2387, the top of each jaw being shown broken
away, so as to fully expose the brasses. S is a square held firmly
against the side face of a jaw, the brasses having their joint faces
true with the square blade, and true also when tested with a square,
applied as in Fig. 2388, in which B is the brass and S the square. The
brasses at the other end should be filed true to the side faces of the
strap in a similar manner, and, the fitting being completed, it simply
remains to mark off the brasses for boring. The joint faces of the
brasses should form the centre of their respective bores; hence, all
that is necessary, is to insure that the brasses be of equal thickness,
top and bottom, and this may be accomplished as follows: Mark across
each face a line even with the ways of the brass, as shown in Fig. 2389,
at A, C, and carry these lines around the side face, as shown in the
figure at B, D. Place the brasses in the strap, put in a piece of wood
whereon the compasses may be rested, as shown in Fig. 2390, which
represents one jaw, and mark on this piece of wood a line even with the
joint faces of the brasses, and on this line a centre-punch dot
equidistant between the lines B, D. From this dot, as a centre, strike
the circle shown, and define it by centre-punch dots, and if the
lathe-hand chucks the brasses true to the ways that fit the rod jaws,
and to the dotted circle, the bores will stand true in every respect.
[Illustration: Fig. 2388.]
[Illustration: Fig. 2389.]
[Illustration: Fig. 2390.]
REPAIRING CONNECTING RODS.--In repairing connecting rods the following
is the work usually required to be done, and in the order named:
Refitting straps, refitting gibs, and perhaps new gibs and keys, filing
up the side faces of rod ends and straps, lining up brasses to make them
fit the strap, lining up the rod to length and fitting the brasses
together so as to fit their journals.
[Illustration: Fig. 2391.]
If the strap is taper and can be closed by pening, the outside of the
back should be pened; but if the strap requires closing in the
blacksmith's shop, then it should be tested by winding strips as shown
in Fig. 2391, to insure that the faces are true, and thus save filing at
the key ways and on the side faces to make them come fair with the rod
ends. The rod ends should then be filed up and the straps fitted on.
[Illustration: Fig. 2392.]
[Illustration: Fig. 2393.]
[Illustration: Fig. 2394.]
Next comes putting in the new key and gib, or refitting the old gib. If
the jaw of the gib has cut into the strap, as it will do in some cases
(especially in marine and locomotive rods), this may be repaired as
follows: Cut out the recess shown in Fig. 2392 at A, making it
dovetail-shaped as shown, and with a set chisel set up its sides as
shown in Fig. 2393, which is a sectional side elevation through the line
of B. Cut out a piece of wrought iron and bevel its edges as shown in
Fig. 2394, filing it to fit into the recess cut at A, Fig. 2392, and
letting the bevelled edge be uppermost. Then take a set chisel and close
down again upon the bevelled edge of the piece the metal that was set
up, as shown in Fig. 2393, and the piece will be riveted, and it and the
gib jaw may be refitted to touch the piece thus let in.
[Illustration: Fig. 2395.]
The jaws of the gib are sometimes made slightly taper at A, Fig. 2395.
To refit the brasses to the jaws of the strap, the flanges which do not
as a rule wear much are usually tinned with a soldering iron, and given
a lining of babbitt metal. This must be done all around the flanges (of
both pairs of brasses) that come on the same side of the rod, so as to
keep the faces of the brasses leading fair.
[Illustration: Fig. 2396.]
The fit between the jaws is restored by riveting pieces of sheet brass
to that side of the brasses that has worn the most (usually the top
which carries the weight of the rod). Fig. 2396 shows this operation
carried out, A being the pieces of sheet brass which are sometimes
soldered as well as held by rivets. These rivets are screwed into the
brass, being composed of softened brass wire riveted after being screwed
in.
If these pieces, which are called liners, are placed on the top of the
brasses at one end, they should also be placed at the top of the brasses
at the other end of the rod. They should not be less than about the 1/24
inch thick, the body of the brass being cut off to admit them if
necessary.
In filing the joint faces of the brasses to let them together so as to
take up the lost motion due to the wear of the brass bore and of the
crank pin, the following considerations are met.
[Illustration: Fig. 2397.]
If the brass faces are to come "brass and brass," that is, butt
together, when their bore is of the diameter of the journal, file those
faces away until the bore appears just perceptibly too large for the
journal, when measured with calipers, as in Fig. 2397, the bore
measuring parallel all the way through. But, in doing this, it is
necessary to be careful to file each brass so that it shall embrace
one-half the journal diameter, which will be the case when the two
brasses measure correctly as above, and alike, when tested, as in Fig.
2398, in which P is a planed surface, C a pair of inside calipers, and B
a brass resting on P. When filing the joint faces, test them with a
square as in Fig. 2399, in which _s_ is a square and B a brass, and also
in Fig. 2400, in which _s_ is a square and B the brass shown in section,
thus making the faces quite square.
[Illustration: Fig. 2398.]
[Illustration: Fig. 2399.]
[Illustration: Fig. 2400.]
The necessity of having their faces quite square when the brasses come
brass and brass may be shown as follows:--
[Illustration: Fig. 2401.]
Suppose the joint to be at an angle as at A, A, Fig. 2401, instead of
square across, as denoted by the dotted lines B, B, then the respective
brasses will be forced by the key-pressure in the direction of the
respective arrows, and there will be a tendency to twist the brasses in
the strap. Or suppose the joint faces to be out of square as at C, C,
instead of square as at D, then there will be a tendency to twist the
respective brasses in the direction of E, F, and therefore to cause
these to move in the direction of G, H, and as a result the brasses will
spring the strap away from the rod, as shown at I, J.
[Illustration: Fig. 2402.]
To line up the brasses for length we proceed as follows: One of the
liners adjusts the length of the rod and the other simply serves to set
the key back to its proper height, so that it shall not pass too far
through the keyway, as the wear of the brasses lets it down. Which of
the liners will be the one by which to alter or adjust the length of the
rod depends upon the design of the rod itself; but, in the case of all
solid-ended rods, or those in which the position of the strap is fixed
by means of bolts, it is the liner behind the end brass, as D, in Fig.
2402, as stated in the opening of this discussion, and it is the first
one, therefore, to be fitted. The space at E is where the second liner
requires to be placed, its thickness being that necessary to lift up the
key from its bottom or lowest position, as shown in the cut, to the
highest position.
[Illustration: Fig. 2403.]
In strap-ended rods in which the strap is not bolted to the rod, but
moves farther upon the rod as the key passes farther through the keyway,
it is the brass next to the rod end, as B, in Fig. 2403, by which to
adjust the length of the rod, and its liner L is, therefore, the one to
be fitted first; the space E is, in this case, the one to be fitted with
a liner of sufficient thickness to lift the key up. It will now be noted
that the thickness of L in both figures requires to be exact, so that
the rod may be of correct length, which is necessary, so that there may
be the same amount of clearance or space between the piston head and the
cylinder cover when the piston is at the respective ends of the stroke.
But the liners to fill the respective spaces E need not necessarily be
of the exact thickness (although it is better that they should be),
because if too thin the only effect will be that the key will pass
farther through the keyway than otherwise. In considering in any form of
rod which is the liner to be put in first to bring the rod to length, we
have the general rule that the brass that moves in the strap or rod end
when the key is moved farther through the keyway is the one to be lined
last. The method of obtaining the proper thickness of the liners L,
Figs. 2402 and 2403, are as follows: If the rods have been correctly
made at first, the centre of the brass bores will be midway in the
spaces for the brasses (denoted by F in the two figures). If the
oil-holes in the strap or rod end (as the case may be) have been drilled
in the centre of this space F as they should be, then the line _g_ will
represent the centre of F and the centre of the oil-holes, and all that
will be necessary will be to place behind D and B respectively a liner
of sufficient thickness to bring the joint face of these brasses (D and
B) even with the line _g_. To ascertain the thickness of liner necessary
for this purpose, suppose the case of a rod end of the design shown in
Fig. 2402, then, with the strap off the rod, drive the brass D down
until its crown face beds fairly against the strap C, and with a scriber
mark on the inside face of the jaw of the strap a line coincident with
the joint face of the brass, then set the brass up the strap until its
joint face comes fair with the centre of the oil-hole or the central
line _g_, and then mark a second line so that on taking the brass out of
the strap there will appear two lines, and the distance between these
two lines is the necessary thickness of liner. In the case of the form
of rod end shown in Fig. 2403, the process would be as follows: Let the
strap have placed in it the brass B only, place it upon the rod, and set
it so that it binds the gib and key, when the key is lifted up to its
required position, then, with the brass B bedding fairly against the rod
end, mark on the strap a line coincident with the joint face of the
brass as before. Then move the brass in the strap until its face comes
fair with the centre of the oil-hole or line _g_, and mark another line,
and the thickness between these lines is the thickness of liner required
at L.
[Illustration: Fig. 2404.]
[Illustration: Fig. 2405.]
[Illustration: Fig. 2406.]