valve is set as follows: Upon the face or edge of the fly-wheel an arc,
true with the centre of the wheel, should be drawn, as at A B, in Fig.
2551, marking it on opposite sides of its diameter and opposite to the
crank pin P. The engine should then be moved in the opposite direction
to that in which it is to run, until the guide block I is very near its
full travel. A straight-edge must then be placed to bear against, or be
coincident with, the end face of block I, and held firmly while a line
is drawn across the edge of the guide bars, as shown at C. There should
then be fastened to the floor (which must be firm, and not give under
the engineer's weight), a piece of iron W, having a deep centre-punch
mark, or its equivalent. A steel tram-rod T, pointed at each end, is
then set in the centre-punch mark at W, and with the upper end D a line
made across the wheel edge or face. The fly-wheel must then be moved so
that the crank passes the dead centre, the guide block moves back and
away from the line C, and then approaches it again. When the end of the
guide block is again coincident with the line C, the tram should be set
as before and a second line, F, marked on the fly-wheel rim, and from
these two lines, D and F, the crank may be placed upon its true dead
centre as follows:--
[Illustration: Fig. 2552.]
In Fig. 2552 a section of the fly-wheel rim is shown (enlarged for
clearness of illustration); from the lines D, F the centre E is found,
and marked with a centre punch dot to define it. It will be obvious,
then, that if the fly-wheel be moved until this line and dot come fair
with the upper edge of the tram T, the guide block will be at the exact
end of its travel, and the crank, therefore, on its dead centre. By a
similar operation performed with the guide block at the other end of the
guide bars, and with lines on the other side of the wheel rim (as shown
at B, J, K), the other centre L may be found. In obtaining these
centres, however, a question arises as to the direction in which the
wheel should be moved for bringing the guide block up to the lines at C,
and for marking the lines D F and J K, or for bringing E or L true with
the tram point. If the fly-wheel be moved in the opposite direction to
that in which the engine is to run, the cross-head journal and crank pin
will bear against the boxes of their brasses in the direction in which
they will have contact when the engine is running. Suppose, for example,
that the top of the fly-wheel when the engine is in motion moves from
the cylinder, then the cross-head and crank-pin journals, driven by the
piston, will bear against the half-brass nearest to the cylinder, which,
_when the force-producing motion is applied to the fly-wheel instead of
to the piston_ will be the case when the fly-wheel is moved in the
opposite direction. By moving the fly-wheel in an opposite direction to
that in which the engine is to run, the lost motion in the journals and
bearings is therefore taken up in the proper direction so far as the
connecting-rod brasses are concerned, and any lost motion between them
and their journals will not impair the set of the valve, as would be the
case were the fly-wheel moved in the direction in which it is to run.
But by moving the fly-wheel backwards the play in the eccentric and in
all the joints between it and the valve spindle is up in the wrong
direction, because the power to move the rods is being applied in the
opposite direction to that in which it will be applied when the engine
is running, and, therefore, the play motion of the jointed or working
parts will cause a lost motion impairing the set of the valve.
Now there are generally more working parts between the eccentric and the
valve than between the crank pin and the piston, and hence more
liability for lost motion to exist, and it follows that in such case it
is better to move the engine in the direction in which it is to run.
It may be remarked, however, that the play may be taken up in the proper
direction in both cases, and the engine be brought upon its dead centre,
by moving it in the opposite direction to that in which it is to run,
and that in setting the eccentrics they be moved on the shaft in the
direction in which the engine is to run, as forward for the forward
eccentric, and backward for the backward one (assuming the engine to
have a link motion, and, therefore, two eccentrics).
It is obvious that any other resting place may be used instead of the
floor for the tram; thus in a locomotive the wheel guard may be used,
the tram T being used to mark lines on the upper part of the wheel rim,
instead of opposite the crank. To set the valve, place the fly-wheel on
its dead centre, moving the fly-wheel as directed until one of the
points (E or L, say E) comes fair with the point of the tram; then move
the eccentric on the shaft until the steam port is open to the required
amount of lead, and fasten the eccentric to the main shaft. Next move
the fly-wheel around until on the opposite dead centre, and if the lead
is the same in amount for both ports the valve is set. Suppose, however,
that in this last case the lead is too great; then it shows that the
eccentric rod is too long, and it must be shortened to an amount equal
to half the difference in the lead. Or suppose that the lead when the
wheel was tried on the last dead centre L, was less than for the other
port; then the eccentric rod must be lengthened to half the amount of
the difference. Assuming that the rod was too long by 1/32 of an inch,
then it may very often be shortened by simply heating about six inches
of its length to a low red heat, and quenching it in water. If the rod
has a foot which bolts on a corresponding foot on the eccentric, then to
lengthen it a liner of the requisite thickness may be placed between the
two feet.
[Illustration: Fig. 2553.]
Suppose there is an equal amount of lead at each end but the amount is
not sufficient or is too great: then the eccentric must be moved on the
shaft until the proper amount of lead appears at the port. The lead must
then be again tried at the other dead centre. In moving the eccentric,
however, it must, under all conditions, be moved in the direction in
which it will rotate, for reasons already given. The best method of
measuring the lead where the lines on a rule cannot be seen is with a
lead wedge P, as shown in Fig. 2553; this, if slightly forced in, will
mark itself, showing how far it entered.
[Illustration: Fig. 2554.]
In some practice the position of the valve is transferred to the valve
stem outside of the stuffing box or gland, as shown in Fig. 2554,
sectional view. The valve stem being disconnected from the rod or arm
that drives it, the valve is moved by hand to have the proper lead, as
at A; a centre-punch mark is then made outside the stuffing box and a
tram B rested thereon; with the other end of the tram a mark C is made
on the valve stem. A similar mark is made on the stem when the crank is
on the other dead centre, and the tram and marks, applied as shown, are
employed instead of measuring the lead at the ports themselves. This
involves extra work, but gives no more correct results. It involves
marking lines on the valve stem, which is objectionable. If several
trials have to be made there is a confusion of lines on the valve stem,
and the wrong one is apt to be taken. On the other hand it affords a
facility for setting the valve without having the steam chest open,
which may in some cases be desirable. If this plan be adopted the lines
on the valve rod should not be defined by centre-punch marks, for they
will cut the packing in the stuffing box.
When the eccentrics are secured to the shaft by a set-screw only, and
not by a feather, it is an excellent plan, after they are finally set,
to mark their positions on the shaft, so that if they should move they
may be set to these marks without moving the engine around.
For this purpose take a chisel with the cutting end ground to the form
of a fiddle drill, one cutting edge being at a right angle to the other.
The chisel must be held so that while one edge rests upon the axle, the
other edge will bear against the radial face of the eccentric. A sharp
blow with a hammer upon the chisel head will make a clean indented cut
upon the axle and the eccentric, the two cuts exactly meeting in a point
where the eccentric bore meets the axle circumference, so that when they
coincide the eccentric is in its proper position.
If the eccentrics of a locomotive should slip when the engine is upon
the road, and there are no marks whereby to readjust them, it may be
done approximately as follows:--Put the reverse lever in the end notch
of the forward gear, then place the crank as nearly on a dead centre as
the eye will direct, and open both the cylinder cocks, then disconnect
the slide-valve spindle from the rocker arm, and move the valve spindle
until the opening of the port corresponding to the dead centre on which
the crank stands will be shown by steam blowing through the cylinder
cock, the throttle valve being opened a trifle. The position of the
valve being thus determined, the eccentric must be moved upon the shaft
until the valve spindle will connect with the rocker arm without being
moved at all. The throttle valve should be very slightly opened,
otherwise so much steam will be admitted into the cylinder that it will
pass through any leak in the piston and blow through both cylinder cocks
before there is time to ascertain which cock first gives exit to the
steam.
Instead of finding when the crank pin is on the dead centre by means of
the process shown in Fig. 2551, it may be found as in Fig. 2555, which
is for a vertical engine. On the face of the crank and from the centre
of the crank shaft as a centre, draw a circle B equal in diameter to the
diameter of the crank pin. Then take a spirit-level C and apply it to
the cylinder bore and note where its bubble stands. Then apply the
spirit-level to the perimeter of the crank pin A and circle B, and move
the crank until the spirit-level bubble stands in the same position as
it occupies when applied to the cylinder bore. If the cylinder bore
stands truly vertical the bubble will in both cases stand in the middle
of the spirit tube; but in any event, the bubble must stand in the same
position when applied to the crank as when applied to the cylinder
bore, in which case the crank will be on its dead centre whether the
cylinder bore be horizontal, vertical, or at an angle, the dotted line E
passing through the centre of the crank and the axis of the cylinder
bore.
[Illustration: Fig. 2555.]
When an engine has two eccentrics, so as to enable the engine to run in
either direction, as in the case of a locomotive, it is necessary to
consider which eccentric is to be set for the forward, and which for the
backward motion. In American locomotive practice it is usual to let the
eccentric nearest to the wheel, and, therefore, the most difficult to
get at, be for the backward motion, which is the least used, and
therefore the least liable to get loose upon the axle.
The eccentric that connects to the top of the link is usually that for
the forward motion, and hence that which connects with the eccentric
farthest from the wheel.
In testing the lengths of the eccentric rods, work may be saved after
the engine is first placed on its dead centre by putting the
reverse-lever in the forward notch of the link, and adjusting the
forward eccentric until the valve has the proper lead. Then set the
reverse-lever in the back notch and move the backing eccentric (in both
cases moving them in the direction in which they will run), until the
proper amount of lead appears. The engine may then be placed on the
other dead centre, and the lead both for forward and backward gear
measured, so that if there are any errors both the rods may be corrected
for length; but for the final trial the crank pin must be set on its
dead centre for each direction of motion separately, so as to take up
any lost motion in the connecting-rod brasses.
[Illustration: Fig. 2556.]
In the case of large marine engines it is not practicable to move or
rotate the engines to set the valves, and the eccentrics are therefore
adjusted to their positions on the crank shaft by lines before the crank
shaft is put into its place or bearings. First, the throw of the crank
is set to stand horizontally true by the following method: From the
centre of the crank shaft strike a circle of the diameter of the crank
pin, as shown in Fig. 2556, at A, and draw upon the face of the crank a
line that shall just meet the two circles as denoted by the line B,
using a straight-edge, one end of which rests upon the crank pin, while
the other end is coincident with the perimeter of the circle A.
[Illustration: Fig. 2557.]
By means of the wedges shown at C D adjust the crank until the line B
stands horizontally level, tested by a spirit-level. A straight-edge
having straight and parallel edges is set horizontally level, beneath
the eccentric, so that its edges will stand parallel with the throw line
of the crank. On this straight-edge, and parallel to the edges, is
marked the line A A, Fig. 2557. The first process is to mark on A A the
centre of the crank shaft K, which is done as follows: Over K is placed
the fine line B B, suspending the weights or plumb bobs at B B;
coincident with this line and across A A, are marked two lines C D;
midway between C D is marked E, which therefore stands directly beneath
the shaft centre. From E the line F is drawn distant from E to the
amount of lap added to the lead the valve is to have. From F as a centre
two lines are drawn across A, their distance apart equalling the full
diameter of the eccentric; the plumb line is then placed over the
eccentric, and the latter is rotated on the shaft until the plumb lines
come exactly fair with the lines G H.
[Illustration: Fig. 2558.]
It is obvious that instead of using plumb lines a square may be employed
to mark the lines C D, and to set the eccentric to the lines G H, the
square being applied as at S and S´, in Fig. 2558.
[Illustration: Fig. 2559.]
In this example it has been assumed that the direction of crank rotation
was to be as denoted by the arrow; but, suppose the crank rotation
required to be in the opposite direction, then the marks on the
straight-edge would require to be located precisely the same, but the
position of the eccentric throw-line would require to be as in Fig.
2559, the perimeter of the eccentric being set to the lines G H as
before. The eccentric rod being supposed to connect direct to the valve
spindle, without the intervention of a rock shaft, for if there is no
rock shaft the eccentric leads in the direction of rotation, while if
the engine has a rock shaft the eccentric follows the crank-pin in the
direction of rotation, and F must be marked on the crank-pin side of E,
as in Fig. 2560.
[Illustration: Fig. 2560.]
[Illustration: Fig. 2561.]
If two eccentrics are used, as in a link motion, the lines for setting
one eccentric are equally applicable to both; the lap and lead line F
being located on the crank-pin side of E when there is a rock shaft, as
is supposed to be the case in Fig. 2561; and on the other side of E when
there is no rock shaft; and in this case the eccentric that is to
operate the valve to make the engine run forward must have its
throw-line following the crank pin, as at J, in Fig. 2561; the eccentric
K operating the valve for running backward. Conversely, in the absence
of a rock shaft, the throw-line of the forward eccentric leads, while
that of the backward eccentric follows the crank pin.
When the line of connection of the eccentric rod is not parallel to the
axial line of the cylinder bore, the crank must be placed horizontally
level (or if it be a vertical engine, on the dead centre), but instead
of the straight-edge being placed parallel to the throw-line of the
crank, it must be placed at a right angle to the line of connection of
the eccentric rod.
[Illustration: Fig. 2562.]
Thus in Fig. 2562 the engine is supposed to be a vertical one, and the
crank is, therefore, placed on its dead centre, its throw-line being
vertical instead of horizontal as in our previous examples (which were
supposed to be for a horizontal engine). It is also supposed to have a
rock shaft A; hence the straight-edge is set at a right angle to the
line of connection of the eccentric rod which is denoted by B.
It is obvious that to set the crank throw-line vertical the circle B in
Fig. 2509 may be used, the spirit-level being resorted to to discover
when the crank stands vertical.
[Illustration: Fig. 2563.]
An example in the erection or setting of framed work is shown in Fig.
2563, which represents a side elevation of a frame put together in four
parts, two side and two end frames. A and B are journal bearings
requiring to stand parallel and true one to the other, B being capable
for adjustment in distance from A by means of the adjusting screws G, H.
The bearings C, D, E, F, are to be parallel one to the other and to A,
B. Their proper relative distances apart, and the axes of all the
shafts, are to stand at a right angle to the side frames.
[Illustration: Fig. 2564.]
Fig. 2564 represents an end view of the frame, the ends T being bolted
to the side frames S and S´ at I, J, K, and L.
Now it is obvious that the ways for the bearings A, B, C, &c., may be
trued out, ready to have the brasses fitted before the framework is put
together, and that from their positions they would have to be planed out
at separate chuckings; supposing, of course, the frame to be too large
to be within the capacity of the machine table. It would be difficult to
cut all the surfaces of the bearing ways to stand in the same plane,
unless there were some true plane to which all might be made common for
parallelism.
Furthermore, unless the surfaces where T is fastened to S and S´ are
properly bedded to fit each other, bolting them up would spring and bend
the frames out of their normal planes. To meet these requirements, there
are given to the side frames a slightly projecting surface where the
feet of T meet them, and furthermore, the feet of T themselves project
beyond the sides of T as shown. These projecting pieces may therefore be
planed to a common plane without planing the sides of the respective
frames; and this plane should be as nearly as can be parallel with the
body of each frame surface. The surfaces of the bearing ways may then be
planed parallel to those of the projections, and the jaw surfaces true
to the side surfaces, and all the bearing ways will stand true if the
frames be properly set--when put together with the bolts. But unless the
bedding surfaces at I, J, K, L, be made to bed and fit properly, the
whole truth of the bearing ways and their distances apart across the
framework may be altered. Thus, supposing the feet of T at I and J to
meet S as denoted by the dotted lines O R, and whether the fault lie
with the feet of T or with the projections on S the result will be that
the pressure of the bolts holding I J to S will bend S so that its plane
will be a curve as denoted by the dotted line P P, and the distances
apart of the journal ways B B and D D respectively will be wrong, being
too wide on account of the bend outward of S.
But the feet may touch on the opposite corners, the surfaces of S´ or of
T being out of true or out of full contact, as denoted by the dotted
lines V W on K, L; in this case the frame S´ would be bent to the curve
Q Q, and the journal ways would be too close together.
On the other hand, the want of fit between these surfaces may be in the
direction of the length of the frame instead of the direction of its
height, as has been supposed; or it may be in one direction on one foot
and in another direction on another foot. But in whatever direction it
does exist, it will inevitably bend and twist the frame.
It must not be taken for granted, that because these surfaces have been
planed or milled, that therefore they are true; because frames of this
class cannot, if large, be held without springing them to some extent
from the pressure of the bolts or other devices necessary to hold them
to be cut.
It is not uncommon to plane the surfaces as true as may be, and put the
frames together, bolting them up tight, and then applying the
straight-edge trammel and rule to test the truth, correcting any error
that may be found by inserting pieces of paper, sheet tin or material of
requisite thickness on one side of the surfaces, so as to offset the
error in their fit and bring the framing true; but this is not the
proper way, because it reduces the area of contact, and furthermore
renders a new testing and adjustment necessary whenever the frames are
taken apart. It is better therefore to apply a straight-edge to the
surfaces and true them to it, testing them vertically as by placing the
straight-edge across K L, and longitudinally across S´, at K and the
corresponding projection at the other end of the frame, filing them
until they appear true.
The holes through the frame may be drilled before filing these surfaces,
so as to reduce the area to be filed. Since the end frames T do not in
this example carry any journals or mechanism, the position of T is not
so particular as it otherwise would be; hence, the holes in its feet may
be marked off and drilled independently of the frame, the holes being
drilled a little too small to allow for reaming with the holes in the
frame. The framing will then be ready to put together (all machine work
upon them being supposed to be done). The feet of all such frames should
be planed true, so that the frame, when put together, may stand true and
steady when placed upon a level floor or foundation, and in this case
the distance and parallelism of the feet surfaces will be true with the
ways or bearings, affording much assistance in holding the frame while
putting it together. The height of the holes may be measured and marked
from the feet surface, thus insuring truth as far as height is
concerned. Lines may be drawn or marked on each side frame, at the
proper distance from and parallel with the jaws of the ways A, B, thus
completing on the side frames the marking of the location of the centres
of the holes for bolting the end frames on.
If the frames were of a size to be sufficiently easily handled, the end
frames might be put in their places, and the whole framework set true,
so as to mark the holes in the end frames from those already drilled in
the side frame. But if the use of a crane were necessary to lift them,
it would be better to mark the holes on the end frames, and drill them
before putting the framework together at all, leaving sufficient to ream
out of the holes to bring them fair, notwithstanding any slight error in
drilling them. In this case, a line denoted by the dotted line X in Fig.
2564, should be drawn across the frame, and the holes at I and J be made
equidistant on each side of it, as well as the proper distance apart. X
must be at a right angle to the trued foot surfaces at I J, so as to
cause the side frames to stand vertical while their feet are horizontal.
Supposing now the holes to be drilled and the frames are to be bolted
together, the whole frame may be held temporarily together by bolts
passing through the side frames at each end, or a bolt may be passed
through the holes F to steady it. Indeed, if these holes F have been
accurately bored, a neatly fitting mandrel passed through them should
hold the side frames true. The end frames T having been set to stand at
a right angle to the side frames, and with their holes at I J, &c., as
near fair as may be with the holes in the side frames, two feet, as I J,
may have their holes reamed fair with the holes in the side frames, and
tightly fitting bolts be driven in and screwed firmly home. Before
reaming the other holes (as K L) of each end frame, the jaws to receive
the bearing boxes should be tested for alignment one with the other.
Truth, in this respect, being of the utmost consequence for the
following reasons:
Suppose the bearing ways on one side frame to stand higher than those on
the other, then, the shafts will not stand level in the frame unless
(except in the case of the brasses or boxes in B) the lower brasses are
made of unequal thickness through the crown, to an amount equal to that
of the error. In the case of the brasses in A, C, D, E, the joint faces
of all the brasses of one side frame would require to be made thinner
beneath the journal than above it on the high frame, and thicker beneath
than above on the low frame, This would entail much extra work in
planing, marking, and boring the bearing boxes or brasses, and be an
inferior job when done.
Again, the bores of all the brasses would not be parallel to the crown
or bedding faces, and this error would entail the following extra work:
1. Ascertaining the amount of the error, and allowing for it in marking
the brasses; 2. The setting of the ways of the brasses out of true with
the ways when clinking them for boring; and, finally, extra fitting or
filing the brass bores when fitted with the shafts in place. This extra
fitting would be necessary for the following reasons:
When the surfaces of work are to be parallel, they can be measured with
calipers. Surfaces to be at a right angle can be tested with a square;
those to be in line can be tried with a straight-edge, and in each case
the truth or alignment of the surfaces is tested by contact of the
testing tool. But in the cases where surfaces at an angle are tested or
measured the tools must be set to a line or lines, and the work must be
measured or cut to lines, thus: Suppose it were found that the bedding
surface of the brass B was a certain amount out of alignment with the
corresponding bedding surface on the other side frame, and, by
measurement, this amount determined to be 1/64 inch, then there is a
liability to error in measuring this 1/64. The brasses must be marked
(for boring the same 1/64 out of square, inducing another liability of
error in marking that amount); this marking being done by lines, there
is a liability to error in setting the work to the lines. From these
liabilities to error, it is generally found that work not true in
alignment requires, when it comes to be put together, to have each piece
fitted to its place and corrected for alignment.
But, suppose the ways are made true and in proper alignment, then the
brass bores are simply made of equal thickness at the crown, and on the
sides at a right angle to the inside faces of the ways; and truth, in
these respects, may be measured by actual contact, with the square or
calipers, eliminating the chance of error.
In repairing the machine, or putting in new bearings or brasses; the
measurement and transferring of the error in the ways to the brasses has
all to be gone through with again, and the parts fitted for alignment;
whereas, if the ways are true, the brasses can be made true, and to go
together, with but little, if any, adjustment when tried in their
places.
[Illustration: Fig. 2565.]
The most accurate method of testing the adjustment of the ways is as
follows: Fig. 2565 represents a plan view of the frame; N represents a
straight-edge applied to the surfaces of the jaws _a_ _b_. The method of
applying this straight-edge is to place one end across a jaw, as _a_,
while the other end is elevated above _b_; then, while pressing the end
firmly against _a_, lower the other end to the face of _b_; if its edge
at that end falls fair with _b_, so as just to touch it, the process may
be reversed--one end being pressed to _b_, and the other lowered upon
_a_. By this means, it will not only be discovered whether the jaws _a_
and _b_ stand square across the frame, but also whether the frame on
either side is sprung. A square _c_ may also be rested against N, and
its blade _d_ tested with the side face of the way, as shown. The same
process of testing should be applied to the other jaw faces _e_, _f_.
Suppose, however, that the width between the jaws _a_, _f_ was less than
that between _e_, _b_, then the straight-edge, when pressed to _a_,
would show a space between its edge and _b_; and also a space between
its edge and _e_, when its other end was pressed to _f_; and, when these
spaces were equal in amount, the frames would be set true in one
direction. To test the truth in the other direction, the straight-edge
should be applied after the same manner to the bottom surfaces _g_, _h_.
It will not answer to rest the straight-edge against the two surfaces
and observe their coincidence with its edge, because any error cannot be
sufficiently, readily, or accurately tested by this means. Nor will it
answer to test by the bearing marks of a straight-edge applied with
marking, unless the coat of marking be very fine and the straight-edge
be moved without any vertical pressure on it; because, under such
pressure, the straight-edge will bend.
The ways for all the bearings should be tested in this manner; so that,
if from any error in the machine work, some of them will not come fair,
the frames may be set to align those that it is of most importance to
align truly; or if there is no choice in this respect, then those
carrying the largest bearing should be set true; because, if it be
decided to correct the error on the other bearing or bearings, there
will be less area to file or operate upon. The setting being complete
the holes may be reamed and the remaining bolts put in, the testing
being repeated after the frame is finally bolted together. If this final
test shows that bolting the frame up has altered the alignment by
springing the frame, the bolts in one foot, as say I, Fig. 2564, may be
slackened and the test repeated; and, if the frame is then found true,
it is the bolting at I that causes the spring, on account of the bedding
surfaces not fitting properly. If I is not found to be at fault, it may
be bolted up again and J tested by loosening its bolts, and so on, until
the location of the error is detected. Furthermore, when the frame is
bolted up, the width of the bearings, as from _a_ to _b_, should be
tested; for in a job of this kind, it will pay to have the framework so
true to the drawing that, if the other parts, as the shafts, bearing
parts, &c., be also made to the drawings, the parts will go together,
thus avoiding the necessity of varying all the other parts from the
drawing to accommodate errors in the framework.
[Illustration: Fig. 2566.]
Among the jobs that the erector is often called upon to perform is that
of patching or repairing pieces that have cracked or broken. Fig. 2566
represents a case of this kind, the fracture being at D. The principle
to be observed in work of this kind is to cause the bolts to force the
fractured pieces together, so that the irregularity or crookedness of
the crack, as at D in the figure, may serve to lock the pieces together.
[Illustration: Fig. 2567.]
Suppose, for example, we were to put on a patch P, Fig. 2567, and there
would be but little to prevent the crack from opening under severe
strain, and the patch would stretch, permitting the crack to open and
finally causing the bolts to break or sheer off. A preferable plan,
therefore, is to put two patches on the sides in the following manner:--
The holes should be drilled through the beam and the plates held against
the beam so that their holes may be marked by a scriber passed through
the holes in the beam. The holes in the plates should be drilled closer
together than those in the beam, so that when driven in they will serve
as keys to close the two sides of the crack together, as shown in Fig.
2568, where it is seen that one side of the bolt bears against the holes
in the patch and the other against the holes in the beam. To facilitate
getting the bolts in place the plates may be heated so as to expand
them.
In cases in which it would not be permissible to drill so many holes
through the beam on account of weakening it, we may use patch bolts with
countersunk heads, as in Fig. 2569. Two only of the bolts pass entirely
through, and it is best to let them be taper, as at A in the figure, the
head not meeting the patch. The hole in the beam, after being reamed
taper, should be filed out on the side B, and that in the patch plates
on the other side, as at C and D, so that the bolts will serve as keys.
After these two bolts are in place and their nuts firmly screwed home,
the holes for the patch bolts may be drilled through the plates and into
the beam. When the countersunk head bolts are fitted they should be
turned down behind the head, so as to leave a part weaker than the bolt,
and then screwed in until the required end breaks off. The taper bolts
should be of steel, but those with countersunk heads may be of iron.
[Illustration: Fig. 2568.]
[Illustration: Fig. 2569.]
ERECTING AN IRON PLANER.--If an iron planer be properly fitted and
erected, the table will be quite solid in the [V]-ways in the bed, and
will not rock or move even though a heavy vertical cut be taken at the
extreme sides of the table, but any error of truth of alignment or fit
either in the bed-ways or the table [V]'s will cause the table to lie
improperly in the [V]'s and to be apt to rock as it traverses. The
author has had planed upon a planer thirty years old, at the Freeland
Tool Works, in New York City, a cast-iron surface 12 × 20 inches, the
metal weighing about 60 lbs., and the surfaces were so truly planed that
one would lift the other by reason of a partial vacuum between the two.
These planed surfaces were exhibited by the author at the American
Institute Exhibition in 1877, and were awarded a medal of superiority.
The manner in which this planer was fitted and erected, and the
principles involved in such fitting and erecting, are as follows:
While it is essential that the foot or resting surface of a planer bed
(whether it stands on legs or rests direct upon its foundation) be as
true as it is practicable to plane it, still it is more essential that
the [V]'s or ways be true, and as the casting will be apt to alter its
form from having the surface metal removed, it is best to plane the side
on which the ways are the last.
When the bed is placed upon the machine to have its resting surface
planed, the casting being uneven, it will be necessary to place packing
pieces of suitable thickness beneath the places where the clamping
plates hold it, so that the pressure of those plates may not spring or
bend the casting.
These packing pieces require to fill up solidly (without lifting the
bed) the hollow places, and it is a good plan to place among them a
piece of strong writing paper for reasons which will appear presently.
In planing the bed all the surfaces should be roughed out before any are
finished. Before any finishing cuts are taken all the clamping bolts
should be loosened and the pieces of paper tried by pulling them, so
that if the casting has altered its form it will be made apparent by
some one of the pieces of paper becoming loose.
In this case the packing must be readjusted, clamping both as lightly as
will hold the work, and all as equally as possible, when the finishing
cuts may be taken.
[Illustration: Fig. 2570.]
The best form of template to plane the ways to is that shown in Fig.
2570, in which B is a side and A an end view. A corresponding female
template being shown at D to be used in planing the table [V]'s.
The length C of the [V] of the template must not be longer than from 4
to 6 inches, or it will be liable to spring or twist from its own
weight. This template is not intended to be used in any sense as a
straight-edge to test the truth of the length of the ways, but rather as
one to test their width apart, and the correctness of the angles. The
top surface A B should be quite true with the [V]'s, being equidistant
from them, so that by testing that surface with a spirit-level it may be
known whether the ways are level either crosswise or lengthwise.
The [V]'s of the template require to have red marking on them so as to
mark the ways when the template is moved, and show that the ways
accurately fit to the template, which is highly important.
In planing the table or platen it is essential to bear in mind that the
area to be planed on the [V] side is always small in comparison with
that to be planed on the other or work-holding side of the table, and as
the planing of this latter surface is sure to cause the casting to alter
its form, it is necessary to plane it first, so that the alteration of
form may occur before and not after the [V]'s have been planed.
In chucking the table to plane its work-holding surface, the packing
pieces must be used as described for the bed, and the bolts placed as
there described.
Both bed and table being planed they require to be fitted together (no
matter how expertly the planing has been done) if a really first-class
job is to be made of them. In doing this it is essential that the bed be
supported at the same points as it will be when the machine is put to
work, for in large or long casting the deflection or bending from its
own weight is sufficient to have an important practical effect. The same
fact will also apply to the table and even to the cross slide, even
though the latter be heavily ribbed and but, say, 5 feet long.
If, therefore, the bed is to be supported by legs, its guideways or
[V]'s should be fitted after the legs are attached. The bed must be
carefully levelled so that the ways may stand horizontally true, which
may be tested by placing the template A B in Fig. 2570 in place and
applying a spirit-level first across and then lengthwise of the upper
surface of the template.
If the bed rests upon a foundation at several points in its length it
should be rested at those points while being fitted and carefully
levelled as before, the template and spirit-level being tried at every
two or three feet of the bed length.
To test the width of the [V]'s and their widths apart in the fitting,
the template A B, Fig. 2570, must be used in connection with red
marking, but to true the lengths of the ways a surface plate about 4
feet long and slightly wider than the width of one side of the ways must
be used, and if the template and the surface plate show the ways true
they will be of the correct width, of correct angle and true planes. But
this does not insure that the two ways are in line one with the other,
and for this purpose separate test blocks are necessary, because the
template is too narrow in width to give a good test, and cannot be made
wider, because in that case its own weight would cause it to spring or
deflect to suit any error in the work.
[Illustration: Fig. 2571.]
These test blocks are simply two pieces of metal, such as shown in Fig.
2571. The lengths of these blocks should be about 8 inches, and the best
way to obtain them true and exactly alike is to make one block and then
cut it into two. They possess an advantage not possessed by a template
that spans both ways, inasmuch as they may be turned end for end in each
way and thus test the accuracy of the angles of each way.
Again, both may be placed in one way, and by various applications in
connection with straight-edge, surface plate, and level they will test
the truth of the ways, both individually and one with the other in a
better manner than by any other method.
Fig. 2572 represents the various positions of the [V] blocks for the
testing, A, B, C, D, E, F, G, H, representing the blocks; straight-edges
may be placed as at I, at J, and at K, and if the ways are true the
straight-edge, lightly coated with marking, should have contact clear
across the upper surface of both [V]-blocks, and a spirit-level placed
on the straight-edge (in each position of the same) should show them to
be level.
The surface P, on which uprights or standards on that side of the plane,
rest, being planed with the [V]-ways will be true with them, and the
uprights may be erected thereon, their base surfaces being fitted to P
until the standards stand truly vertical and parallel in their widths
apart. In testing these uprights they should be bolted home as firmly as
they will be when finally erected, as they will be liable to alter their
set if bolted up more firmly than when tested. These front surfaces
should be at a right angle to the length of the bed [V]-ways, and this
may be tested by placing a straight-edge across their surfaces and
testing it with a square rested against the edge of the planer table.
The method of erecting planers at the Pratt and Whitney Company's shops
is as follows:--
To test the [V]'s, a plate P, Fig. 2573, is applied as shown, its lugs
_a_, _a_^{1} fitting to corresponding sides of the two [V]s; as B, B. In
Fig. 2573 the test is made by inserting thin pieces of tissue paper
between _a_, _a_^{1} and the [V]-sides, the friction with which the
paper is held showing the nature of the fit. Thus, if the paper will
move easily at one end and is tight at the other end of either of the
lugs _a_, _a_^{1} the fit is shown to be defective. When the fit on
these sides is corrected, the plate P is turned around, as in Fig. 2574,
and from a similar tissue-paper test, the other sides are corrected.
Thus the outside angles of the two [V]s are fitted to the same angle;
inside angles are also fitted to the same angle. But it will be observed
that it does not follow that the inside angles of the [V]s are of the
same degree of angle as are the outside halves or angles, unless the two
lugs _a_, _a_^{1} of the plate P have equal angles. It is on this
account that the test is made by tissue paper, rather than by the
bearing marks produced by rubbing P along the [V]s, since that might in
time wear the angles _a_, _a_^{1} out of true. The same plate P may be
used to true the male [V]s on the work-holding table of the machine, as
is shown in Figs. 2575 and 2576, where the table is seen upside down, as
is necessary in order to apply the plate. Here, again, the outside
angles or halves of the [V]s are fitted from the same [V] (_a_^{1}) of
the plate, so that the fit of the table will be true to the bed, even
though the angle on one side of the [V]-ways were not precisely correct,
and there is less liability to error than would be the case were a male
and female plate used instead of a single plate. The alignment next in
importance is that of the uprights, standards, or side frames of a
planing machine, and to enable the correct erection of these, the device
A, Fig. 2577, is employed. It consists of a solid plate fitting into the
[V]-ways of the planer-bed and having two steps, B and C, which receive
the side frames to be erected. The width D is the width apart of the
side frames, and the side surfaces of the steps (as G) are vertical to
the centre line of the [V]-ways of the bed, so that the side frames may
be rested against G on one side, and the corresponding surface on the
other step. The surfaces E, F are at a right angle to the [V]-ways of
the bed, so that when the side frames are against E, F they will be set
square across the machine. The top face of the plate A is planed
parallel to the [V]s of the plate, so that in addition to resting each
side frame against the surfaces (as F G) a square may be rested on plate
A and applied to their trued surfaces, and thus may these side frames be
set true and square, both one with the other, and with the ways in the
bed, without the use of stretched lines and straight-edges, which
secures greater accuracy and saves considerable labor.
[Illustration: Fig. 2578.]
All the smaller parts of the machine may then be erected true to the bed
or the side frames, as may be required, and if it be a small planer, in
which the bed rests upon feet, all that will be necessary in setting the
machine in position to work is to set the surface of the work-table
level. But in the case of a large heavy planer a solid foundation must
be built for the bed, because it will spring, bend, and deflect from its
own weight, and thus the side frames, as well as the bed, may be thrown
out of true and alignment. Fig. 2578 is a side and plan view of the
foundations for a planer, showing the bed-plate in position upon the
same.
[Illustration: _VOL. II._ =TESTING PLANER BEDS AND TABLES.= _PLATE XI._
Fig. 2572.
Fig. 2573.
Fig. 2574.
Fig. 2575.
Fig. 2576.
Fig. 2577.]
The stone blocks forming the base of the foundation require themselves
to rest upon a solid base, and not upon a soil or gravel that is liable
to sink beneath them. The brickwork above them is best laid in cement,
which should be properly set before the planer bed is placed in
position. Near the centre of the bed, and directly beneath the
cross-slide, is shown a screw jack, to take up any sag of the bed, and
cause the [V]s to have a good bearing directly beneath the cutting tool,
which is essential to prevent the table from springing from the pressure
of the tool cut.
FITTING UP AND ERECTING A LATHE.--The first operation will be to true
the bed or shears. If the lathe has raised [V]s on the bed it will be
sufficient to true them only, without truing the flat surfaces. The bed
should during the fitting be supported at the same points as it will be
when in use.
[Illustration: Fig. 2579.]
The method of aligning the lathe heads at the Pratt and Whitney
Company's workshops is as follows: Fig. 2579 is a side and an end view
of a part of a lathe shears A, with the tailstock B thereon. To the bore
of the tailstock there is closely fitted an arbor C, accurately turned
in the lathe, and having at the end D and at E two short sections of
enlarged diameter. A plate F is fitted to the inside [V]s of the shears
(upon which [V]s the tailstock sits). This plate carries a stand G, and
a second gauge or stand G. Stand G fits at its foot into a [V] provided
in F, as shown, the object of which is to so hold G to F that its (G's)
face will stand parallel to arbor C. The stand is so adjusted that a
piece I may be placed between C and G and just have contact with both,
and it is obvious that if this is found to be the case with the
tailstock and the stand placed at any position along the bed, the arbor
C, and, therefore, the bore of the tailstock, must be true, sideways, to
the inside [V]s of the lathe shears. The testing, however, is made at
the enlarged sections D and E, G of course being firmly bolted to F. To
test the height of the arbor C from the [V]s, and the parallelism in
that direction, stand H is provided. It carries a pointer or feeler K,
whose end is adjusted to just touch the enlarged sections D and E of C,
it being obvious that when the degree of contact is equal at these two
sections, with the tailstock and the plate F moved to various positions
along the bed, the adjustment or alignment in that direction is also
correct. The adjustment and corrections may then be made with the
headstock of the lathe in place of the tailstock, the arbor fitting into
the bored boxes of the lathe and extending from it, and having two
sections of the same diameter, as sections E in the figure. Now, suppose
that in the test thus made the bar C proves to stand true in some
locations, but not in others, upon the bed; then it is proof that it is
the [V]s that require correction, while the tailstock is in error in all
cases in which the error is constant, with the tailblock moved in
various positions along the shears.
In some practice the heads are bored after being fitted to the ways, and
in this case the boring bar may be supported by standards fitting to the
lathe bed, running in bearings, and not on centres. There should be
three of these bearings, one at one end of the head, and as close to it
as convenient, another at the other end, as close as will permit the
insertion of the cutters, and the third as far from the second as will
permit the insertion on the bar and between them of a pulley to drive
the bar, which must be splined to receive a feather in the pulley, so
that the bar may be fed through its bearings and through the pulley to
the cut. After the live head has been bored the tailstock or back-head
may be bored from the other end of the bar, so that the standards will
not require to be moved on the bed until the boring is completed. The
bar may be fed by hand, or an automatic feed motion may be affixed to
one of the standards. The heads being secured to the bed while being
bored, there is no liability of error in their alignment, because, even
if the holding bolts spring the heads in clamping them to the bed, the
holes will be true when the heads are firmly home upon the bed, as they
will be when in use, whereas under this condition such will not be the
case if the holes for the spindles are bored before the seats are planed
and fitted.
The feed screw must be placed quite parallel to the [V]s or guides of
the bed, or otherwise the pitches of threads cut in the lathe will be
finer than they should be, and the screw will bind in the feed nut,
causing undue wear to both.
The method employed to test the truth of lathe shears and heads in the
David W. Pond Works, at Worcester, Massachusetts, is as follows:--
[Illustration: Fig. 2580.]
The planing, both of the lathe shears and of the heads, being done as
accurately as possible, the heads are provided with a mandrel or arbor,
to the end of which is secured the device shown in Fig. 2580, in which A
is a hollow cylindrical piece having a threaded and split end, so that
by means of a nut the bore may be closed to tightly fit the arbor
referred to; B, B are two arms, a sliding fit in A, to enable their
adjustment for the width of lathe [V]s, and having a flat place on one
side, as at C C, to receive the pressure of a locking device D, by means
of which B, B may be fastened in their adjusted positions; E, E are
cylindrical arms, a sliding fit in B, B, also having flat sides, and
capable of being secured in their adjusted positions by means of
locking devices F, F.
[Illustration: Fig. 2581.]
[Illustration: Fig. 2582.]
Fig. 2581 is an end view of the device in position on a lathe tail
stock, and Fig. 2582 is an enlarged view (being half full size) of the
devices at the lower end of arms or rods E, E.
At the lower ends of E, E are provided two pieces G, G, which are
capable of adjustment to fit the [V]s H, H of the lathe, as follows:--
The middle pins I are fast in the arms J, but are pivoted in G, the end
pins, as K, are pivoted in G, are flat where they pass through J, and
threaded to receive the nuts, L, of which there are four, two to each
piece G. By operating these nuts, G may be adjusted to bed fair on the
angles on the lathe [V]s H. At M are two fixed pins which afford a
fulcrum, at N and O respectively, to four index needle arms. Two of
these index arms only are seen in the cut, marked respectively P and Q,
which are pivoted at N. Two similar pointer or needle arms are on the
other side of M, being behind P and Q, these two being pivoted
respectively at O. At the lower end of P is a point resting in the
centre of the nut, and similarly the end of Q rests in the centre of the
nut on that side. Similarly the two needles not seen have pointed ends
resting in the centre of the nuts marked respectively L. Between G and J
are two springs placed back to back, which act to hold G away from J.
But it will be seen that if either end of G be forced towards J, as by
passing over a projection on the [V] H, then the pin K, will push nut L,
and this will raise the end of the pointer or needle to a corresponding
degree, and the pointer being pivoted (as at N), its upper end will move
and denote on the graduated index R that there is an error in the lathe
[V], the amount of the error being shown multiplied on account of the
leverage of the needle arms from the pivots.
The pieces G being adjusted to bed fairly on the lathe [V]s, the heads
of the lathe are moved along the lathe shears, and if the [V]s are true
to angle the upper ends of the needles will remain stationary, a
projecting part of a [V] will, however, cause the needle point to move
toward E, while a depression on a [V] would cause the springs K to move
G in, keeping it in contact with the [V], while the needle point would
move away from E. To maintain the needle arms in contact with the nut
heads L, springs S are employed. Variations in the widths apart of the
[V]s on either side of the shears would obviously be shown in the same
manner, the defect being located by the needle movement. The corrections
are made from the contact marks of the heads, caused by moving the heads
along the [V]s and by careful scraping.
Notwithstanding that every care and attention may be taken to make a
lathe true in the process of manufacture, yet when the whole of the
parts are assembled it is found essential to test the truth of the
finished lathe, because, by the multiplication of minute errors the
alignment of the lathe, as a whole, may be found to need correction. A
special inspector is therefore employed to test finished machines before
they leave the works, and in Fig. 2583 is represented the device
employed for testing the alignment of the line of centres of lathes.
Upon the face of the face plate and near its perimeter there are turned
up two steps, as denoted by B and C. The tail-spindle is provided with a
stud S, which fits in the place of the dead centre, and carries what may
be termed a double socket, one-half of which (as F) envelops the stud S,
while the other half (A) envelops and carries a rod R. These two halves
are in reality split sleeves, with set screws to close them and adjust
the fit. By means of the screws E, the sleeve F may be made a tight
working fit upon S, while, by means of screws G, sleeve A may be made to
firmly grip the rod R, which may thus be securely held while still
capable of being swung upon stud S. Upon the outer end of the rod R is
another sleeve I, which is also split and secured to the rod R by means
of screws corresponding to those shown at G. It also carries a pin, upon
which a disk K is pivoted, and a lug through which the adjusting screw V
is threaded. Upon K is a lug which has on one side of it the end of a
spring T, and it is obvious that by operating V the disk K will be
rotated upon its central pin. K carries two lugs, L and M, the latter
being threaded and split. These two lugs receive a sleeve N, threaded
into M, and a close plain fit in L. The small end of this sleeve is
split and is threaded slightly taper, and is provided with the nut P.
Through this sleeve passes a needle Q Q, one end of which is bent as
shown, and it is obvious that by screwing nut P upon N the sleeve will
be closed and will tightly grip the needle Q Q. Now, suppose that the
head of N is operated, and it will move endwise through L and M,
carrying with it the needle Q Q, which will remain firmly clasped in the
sleeve; or suppose that screw V is operated, and K will revolve,
carrying with it the needle Q Q, which will still remain firmly gripped,
and it follows that there is thus obtained a simple means of adjusting
the needle without releasing it.
[Illustration: Fig. 2583.]
The application of the instrument is as follows: To test if the head and
tailstocks are of equal height from the bed, the instrument is set and
adjusted exactly as shown in the engraving, the needle being adjusted to
just touch the diameter of the step at B. The rod R is then swung around
so that the needle comes opposite to the same step B at the bottom of
the face plate, and if the needle just touches there also the adjustment
for tailstock height is correct. Similarly for testing if the tailstock
is set true sideways the needle may be tried in the same manner and upon
the same step, but upon the two opposite sides of the face plate,
instead of at the top and bottom. It now remains to test if the
tailstock is in line in a horizontal direction with the live spindle,
and this is done by reversing the needle end for end in the sleeve N,
and setting it to just touch the face C of the turned step on the face
plate, and if it just touches at the top and bottom as well as at the
two sides the tail-spindle is obviously in line. It may be observed,
however, that if an error in any one direction is found, it is necessary
to go through the whole series of tests in order to precisely locate the
error. Suppose, for example, that the needle, being adjusted as in the
engraving to just touch the step at B, does not touch it when tried at
the bottom of the plate, then the error may be caused in three
ways--thus, in the first place, the whole tailstock may be lower than
the headstock; in the second place, the front end of the tailstock may
be too low; or, in the third place, the back end of the tailstock may be
too high. If the first was the cause, the test with the needle point
tried with face C would show correct. If the second or third was the
cause of the error, the needle point when tried to face C would touch
when applied at the top, but would not touch when tried at the bottom of
the face plate. Another case may be cited. For example, suppose the
needle applied as shown touched at the bottom but not at the top of the
step B, then the test with the needle reversed would show whether the
whole tailstock was too high, or whether the front end only was too
high, or the back end too low. There is one excellent feature in this
device to which attention may be called, which is that the tests are
made on as large a diameter of face plate as possible, which shows the
errors magnified as much as possible.
The same device is used to test if the cross slide of the carriage or
saddle is at a right angle to the lathe shears, the method of its
application being as shown in Fig. 2584. The split sleeve A receives in
this case a rod R, which is laid in the slideway S of the carriage or
saddle, and a long rod H carries the needle-holding devices. The rod R
is held fair against the slideway, and the face of the sleeve A is held
against the edge of the carriage or saddle. The needle Q is then
adjusted to just touch the edge D of the lathe bed. When this adjustment
is made the rod H is swung over to the right and the coincidence of the
needle point again tried with the edge of the lathe bed, the cross
slideway being at a right angle when the needle point touches the edge D
of the lathe bed when tried on the left hand, and also on the right
hand, of the carriage. The stiffening rod U is brought under tension by
a nut operated against a lug on X. To counterbalance the overhanging
weight of the rod H and its attachments, a rod carrying a weight W is
employed. It is obvious that the truth of the operation depends wholly
upon the straightness and parallelism of the enlarged sections P of the
rod R, upon keeping the end face of A in contact with the carriage at Z,
and upon the correct adjustment of the needle to the edge of the lathe
bed.
[Illustration: Fig. 2584.]
SETTING LINE SHAFTING IN LINE.--The following method of adjusting line
shafting or setting it in line, as it is termed, is that generally
adopted in the best practice.
[Illustration: Fig. 2585.]
[Illustration: Fig. 2586.]
[Illustration: Fig. 2587.]
First prepare a number of rude wooden frames, such as shown in Fig.
2585. They are called targets, and are pieces of wood nailed together,
with the outer edge face A planed true, and having a line marked
parallel with the planed edge and about three-quarters of an inch inside
of it. Upon this frame we hang a line suspending a weight and forming a
plumb-line, and it follows that when the target is so held that the
plumb-line falls exactly over and even all the way down with the scribed
line, the planed face A, Fig. 2586, will stand vertical. To facilitate
this adjustment, we cut a small [V] notch at the top of the scribed
line, the bottom of the [V] falling exactly even with the scribed line,
so that it will guide the top of the plumb-line even with the scribed
line at the top; hence the eye need only be directed to causing the two
lines to coincide at the bottom. To insure accuracy, the planed edge A
should not be less than a foot in length. Then tightly stretch a strong
closely-twisted and fine line of cord beside the line of shafting, as
shown in Fig. 2587, placing it say six inches below and four inches on
one side of the line of shafting, and equidistant at each end from the
axial line of the same, adjusting it at the same time as nearly
horizontally level as the eye will direct when standing on the floor at
some little distance off and sighting it with the line shaft.
In stretching and adjusting this line, however, we have the following
considerations:--It must clear the largest pulley hub on the line of
shafting, those pulleys having set-screws being moved to allow it to
pass. If the whole line of shafting is parallel in diameter, we set the
line equidistant from the shafting at each end. If one end of the
shafting is of larger diameter, we set the line farther from the surface
of the shafting, at the small end, to an amount equal to one-half of the
difference in the two diameters; and since the line is sufficiently far
from the shafting to clear the largest hub thereon, it makes, so far as
stretching the line is concerned, no difference of what diameter the
middle sections of shafting may be. The line should, however, be set
true as indicated by a spirit-level.
We may now proceed to erect the targets as follows: The planed edge A in
Fig. 2585 is brought true with the stretched line, and is adjusted so
that the plumb-line B in Fig. 2586 will stand true with the line or mark
B. When so adjusted, the target is nailed to the post carrying the
shafting hanger. In performing this nailing, two nails may be slightly
inserted so as to sustain the target, and the adjustment being made by
tapping the target with the hammer, the nails may be driven home, the
operator taking care that driving the nails does not alter the
adjustment.
[Illustration: Fig. 2588.]
In Fig. 2588 A A represents the line of shafting, B, B two of the hanger
posts, and C, C two of the adjusted targets.
[Illustration: Fig. 2589.]
We have now in the planed edges A of the targets a rigid substitute for
the stretched line, forming a guide for the horizontal adjustment, and
to provide a guide for the vertical adjustment we take a wooden
straight-edge long enough to reach from one post to another. Then
beginning at one end of the shafting, we place the flat side of the
straight-edge against the planed edge of two targets at a distance of
about 15 inches below the top of the shafting; and after levelling the
straight-edge with a spirit-level, we mark (even with the edge of the
straight-edge) a line on the planed edge of each target, and we then
move the straight-edge to the next pair of targets, and place the edge
even with the mark already made on the second target. We then level the
straightedge with a spirit-level, and mark a line on the third target,
continuing the process until we have marked a straight and horizontally
level line across all the targets, the operation being shown in Fig.
2589, in which A represents the line of shafting, B the hangers, and C
the targets. D represents the line on the first target, and E the line
on second. F is the straightedge, levelled ready to form a guide whereby
the line D may be carried forward, as at E, level and straight, to the
third target, and so on across all the targets.
[Illustration: Fig. 2590.]
[Illustration: Fig. 2591.]
The line thus marked is the standard whereby the shafting is to be
adjusted vertically; and for the purpose of this adjustment, we must
take a piece of wood, or a square, such as is shown in Fig. 2590, the
edges A and B being true and at a right angle to each other. The line D,
in Fig. 2589, marked across the targets being 15 inches below the centre
line of the shaft at the end from which it was started, we mark upon our
piece of wood the line C in Fig. 2590, 15 inches from the edge A (as
denoted by the dotted line); and it is evident that we have only to
adjust our shaft for vertical height so that, the gauge being applied at
each target in the manner shown in Fig. 2591, the shaft will be set
exactly true, when the mark C on the piece of wood comes exactly fair
with the lines D marked on the targets.
[Illustration: Fig. 2592.]
For horizontal adjustment, all we have to do is to place a straight-edge
along the planed face of the target, and adjust the shaft equidistant
from the straight-edge, as shown in Fig. 2592, in which A is the shaft,
B the target, C the straight-edge referred to, and D a gauge or distance
piece. If, then, we apply the straight-edge and wood gauge to every
target, and to the adjustment, the whole line of shafting will be
complete.
There are several points, however, during the latter part of the process
at which consideration is required. Thus, after the horizontal line,
marked on the targets by the straight-edge and used for the vertical
adjustment, has been struck on all the targets, the distance from the
centre of the shafting to that line should be measured at each end of
the shafting, and if it is found to be equal, we may proceed with the
adjustment; but if, on the other hand, it is not found to be equal, we
must determine whether it will be well to lift one end of the shaft and
lower the other, or make the whole adjustment at one end by lifting or
lowering it, as the case may be. In coming to this determination we must
bear in mind what effect it will have on the various belts, in making
them too long or too short; and when a decision is reached, we must mark
the line C, in Fig. 2590, on the gauge accordingly, and not at the
distance represented in our example by the 15 inches.
The method of adjustment thus pursued possesses the advantage that it
shows how much the whole line of shafting is out of true before any
adjustment is made, and that without entailing any great trouble in
ascertaining it; so that, in making the adjustment, the operator acts
intelligently and does not commence at one end utterly ignorant of where
the adjustment is going to lead him to when he arrives at the other.
Then, again, it is a very correct method, nor does it make any
difference if the shafting has sections of different diameters or not,
for in that case we have but to measure the diameter of the shafting,
and mark the adjusting line, represented in our example by C, in Fig.
2590, accordingly, and when the adjustment is complete, the centre line
of the whole length of the line of shafting will be true and level. This
is not necessarily the case, if the diameter of the shafting varies and
a spirit-level is used directly upon the shafting itself.
In further explanation, however, it may be well to illustrate the method
of applying the gauge shown in Fig. 2590, and the straight-edge C and
gauge D shown in Fig. 2592, in cases where there are in the same line
sections of shaftings of different diameters. Suppose, then, that the
line of shafting in our example has a mid-section of 2-1/4 inches
diameter, and is 2 inches at one, and 2-1/2 inches in diameter at the
other end: all we have to do is to mark on the gauge, shown in Fig.
2590, two extra lines, denoted in figure by D and F. If the line C was
at the proper distance from a for the section of 2-1/4 inches in
diameter, then the line D will be at the proper distance for the section
of 2 inches, and E at the proper distance for the section of 2-1/2
inches in diameter; the distance between C and D, and also between C and
F, being 1/8 inch, in other words, half the amount of the difference in
diameters.
In like manner for the horizontal adjustment, the gauge piece shown at D
in Fig. 2592 would require when measuring the 2-1/4 inch section to be
1/8 inch shorter than for the 2 inch section, while for the 2-1/2 inch
section would require to be 1/8 inch shorter than that used for the
2-1/4 inch section, the difference again being one-half the amount of
the variation in the respective diameters. Thus the whole process is
simple, easy of accomplishment, and very accurate.
If the line of shafting is suspended from the joists of a ceiling
instead of from uprights, the method of procedure is the same, the forms
of the targets being varied to suit the conditions. The process only
requires that the faced edges of the targets shall all stand plumb and
true with the stretched line. It will be noted that it is of no
consequence how long the stretched line is, since its sag does not in
any manner disturb the correct adjustment, but in cases where it is a
very long one it may be necessary to place pins that will prevent it
from swaying by reason of air currents or from jarring.
The same system may be employed for setting the shafting hangers, the
bores of the boxes being used instead of the shafting itself.
CHAPTER XXX.--LINE SHAFTING.
LINE SHAFTING.--A line of shafting is one continuous run or length
composed of lengths joined together by couplings. The main line of
shafting is that which receives the power from the engine or other
motor, and distributes it to other lines of shafting, or to the various
machines to be driven. In some practice each line of shafting is driven
by a separate engine or motor, so that it may be stopped without
stopping the others. This same object may be obtained by providing a
clutch for each line. It is obvious that in each line of shafting the
length nearest to the driving motor transmits the whole of the power
transmitted by the line, and that the diameter of the shafting may,
therefore, be reduced as it proceeds from the engine in a proportion
depending upon the degree to which the power it is required to transmit
is reduced. It is desirable, therefore, so far as the shafting is
concerned, to place the machines requiring the most power to drive as
near as possible to that end of the shafting that receives power from
the motor. Line shafting is supported in bearings provided in what are
termed hangers, which are brackets to be bolted to either suitable
framing, to walls, posts, or to the ceiling or floor of the building.
The short lengths of shafting that are provided to effect changes of
speed, and to enable the machine to be stopped or started at pleasure,
are termed countershafts. When there is interposed a countershaft
between the motor and the main line of shafting, it is sometimes termed
a jack shaft.
Shafting is usually made cylindrically true either by special rolling
processes as in what is known as "cold-rolled," or "hot-rolled"
shafting, or else it is turned up in the lathe. In either case it is
termed bright shafting. What is known as black shafting is simply bars
of iron rolled by the ordinary process and made cylindrically true only
where it receives its couplings, and for its journal bearings, &c. The
diameter of black shafting varies by a quarter of an inch, and is
usually above its designated diameter by about 1/32 inch.
The main body of the shafting not being turned cylindrically true and
parallel, the positions of the pulleys cannot be altered upon the
shafts, nor can pulleys be added to the shaft as occasion may require
without the sections being taken down and seatings turned for the
required pulleys to be added. Furthermore black shafting does not run
true, and is in this respect also objectionable. Nevertheless, black
shafting is used for some special cases where extra pulleys are not
likely to be required and the shafting is exposed to the weather, as in
the case of yards for the manufacture of building bricks.
The diameters of bright or turned shafting (which is the ordinary form
in which shafting is made, unless otherwise specified) vary by 1/4 inch
up to about 3-1/2 inches in diameter; but the actual diameter is 1/16
inch less than the denominated commercial diameter, which is designated
from the diameter of the round bar iron from which the shafting is
turned; thus a length of what is known as 2-inch shafting will have an
actual diameter of 1-15/16 inches, being parallel, or as nearly parallel
as it is practicable to turn it in the ordinary lathe.
Cold-rolled shafting has its actual diameter agreeing with its
designated or commercial diameter, and is parallel throughout its
length.
In England the diameters of shafting vary by eighths of inches for
diameters of an inch and less, and by quarters of an inch for diameters
above an inch, the commercial and the actual diameters being alike.
The strains to which a line of shafting is subject are as follows: The
torsional strain due to rotating the line of shafting, independent of
the power transmitted; the torsional strain due to the amount of the
power transmitted; and the transverse strain due to the unequal belt
pressures and distances from the bearings of the driving or transmitting
pulleys. The first and the last are, however, so intimately connected in
practice that they may be considered as one: hence we have, 1st, the
torsional strain due to driving the whole load, and, 2nd, the transverse
strain due to the belt pressures being exerted more on one side than on
another of the shaft, and to the belt pulleys being at unequal distances
from the hanger bearings.
The first may be reduced to a minimum by so proportioning the strength
of the line of shafting that it shall be capable of transmitting the
required amount of power at the various sections of its length without
suffering distortion of straightness beyond certain limits, and shall be
at the same time as light as is consistent with this duty and a certain
factor of safety.
Referring for a moment to the above limitation, the weight of the shaft
itself will cause it to deflect between the hanger bearings, and the
amount of this deflection will depend upon the distance apart of the
points of support, or, in other words, of the distance apart of the
hanger bearings.
The second may be reduced to a minimum by so regulating the distance
apart of the hanger bearings that the deflection of the shaft from the
belt pressures shall not be sufficient to produce sensible
irregularities in the axis of rotation of the shaft; by so connecting
the bearings to the hangers that they shall be rigidly held, and yet
capable as far as possible of automatically adjusting their bores to be
true with the shaft axis, notwithstanding its deflection from any cause;
by placing the pulleys transmitting the most power as near to the hanger
bearings as practicable; by so disposing the driving belts as to deliver
the power as near as possible equally on all sides of the shaft; and by
having the shafting and the pulleys balanced so as to run true, so that
the strains on the pulleys shall be equal at each point in the shaft
rotation. From this it appears that the distance apart of the shafting
hangers may vary according to the amount of power transmitted by a shaft
of a given diameter. The following table (given by Francis) gives the
greatest admissible distances between the bearings of continuous shafts
subject to no transverse strain except from their own weight, as would
be the case were the power given off from the shaft equally on all
sides, and at an equal distance from the hanger bearing.
+----------------+------------------------------------+
| Diameter of | Distance between bearings, in feet.|
|shaft in inches.+--------------------+---------------+
| |Wrought-iron shafts.| Steel shafts. |
+----------------+--------------------+---------------+
| 2 | 15.46 | 15.89 |
| 3 | 17.70 | 18.19 |
| 4 | 19.48 | 20.02 |
| 5 | 20.99 | 21.57 |
| 6 | 22.30 | 22.92 |
| 7 | 23.48 | 24.13 |
| 8 | 24.55 | 25.23 |
| 9 | 25.53 | 26.24 |
+----------------+--------------------+---------------+
These conditions, however, do not usually obtain in the transmission of
power by belts and pulleys, and the varying circumstances of each case
render it impracticable to give any rule which would be of value for
universal application.
For example, the theoretical requirements would demand that the bearings
be nearer together on those sections of shafting where most power is
delivered from the shaft, while considerations as to the location and
desired contiguity of the driven machines may render it impracticable to
separate the driving pulleys by the intervention of a hanger at the
theoretically required location. The nearer together the bearings the
less the deflection either from the shaft's weight or from the belt
stress, and since the friction of the shaft in its bearings is
theoretically independent of the journal-bearing area, the closer the
bearings the more perfect the theoretical conditions; but since it is
impracticable to maintain the true alignment of the shaft, and as the
friction due to an error in alignment would increase with the nearer
proximity of the bearings, they are usually placed from about 7 to 12
feet apart, according to the facilities afforded in the location in
which they are to be erected.
It is to be observed, however, that the nearer together the bearings are
the less the diameter, and, therefore, the lighter the shafting may be
to transmit a given amount of power, and hence the less the amount of
power consumed in rotating the shafting in its bearings.
COLD-ROLLED SHAFTING--This is shafting made cylindrically round and
parallel by means of cold rolling, which leaves a smooth and bright
surface. The effects of cold rolling upon the metal have been determined
by Major Wm. Wade, U.S.A., Sir William Fairbairn, C.E., and Professor
Thurston, of the Stevens Institute, as follows:--
The experiments were made upon samples of cold-rolled shafting submitted
by Messrs. Jones and Laughlins, of Pittsburgh, Pennsylvania.
SUMMARY OF THE RESULTS OBTAINED BY MAJOR WADE FROM NUMEROUS EXPERIMENTS
WITH ORDINARY HOT-ROLLED BAR IRON, COMPARED WITH THE RESULTS OBTAINED
FROM THE SAME KINDS OF IRON ROLLED AND POLISHED WHILE COLD BY LAUTH'S
PATENT PROCESS.
------------------------------------------+-------------+---------+---------
| Iron rolled | Ratio of|Average
| while | increase|rate per
+------+------+ by cold |cent. of
| Hot. | Cold.| rolling.|increase.
------------------------------------------+------+------+---------+---------
TRANSVERSE.--Bars supported at both | | | |
ends; load applied in the middle; distance| | | |
between the supports, 30 inches. Weight | | | |
which gives a permanent set of one-tenth | | | |
of an inch, viz. | | | |
} 1-1/2 inch square bars | 3,100|10,700| 3.451 |}
} Round bars, 2 inch diameter| 5,200|11,100| 2.134 |} 162-1/2
} Round bars, 2-1/4 " " | 6,800|15,600| 2.294 |}
| | | |
TORSION.--Weight which gives a permanent| | | |
set of one degree, applied at 25 inches | | | |
from centre of bars. Round bars, 1-3/4 | | | |
inch diameter, and 9 inches between the | | | |
clamps | 750| 1,725| 2.300 | 130
| | | |
COMPRESSION.--Weight which gives a | | | |
depression, and a permanent set of | | | |
one-hundredth of an inch to columns 1-1/2 | | | |
inches long and 5/8 inch diameter |13,000|34,000| 2.615 | 161-1/2
Weight which bends and gives a permanent | | | |
set to columns 8 inches long and 3/4 inch | | | |
diameter, viz. | | | |
} Puddled iron |21,000|31,000| 1.476 |}
} Charcoal bloom iron |20,500|37,000| 1.804 |} 64
| | | |
TENSION.--Weight per square inch, which | | | |
caused rods 3/4 inch diameter to stretch | | | |
and take a permanent set, viz. | | | |
} Puddled iron |37,250|68,427| 1.837 |}
} Charcoal bloom iron |42,439|87,396| 2.059 |} 95
Weight per square inch, at which the same | | | |
rods broke, viz. | | | |
} Puddled iron |55,760|83,156| 1.491 |}
} Charcoal bloom iron |50,927|99,293| 1.950 |} 72
| | | |
HARDNESS.--Weight required to produce | | | |
equal indentations | 5,000| 7,500| 1.500 | 50
------------------------------------------+------+------+---------+---------
NOTE.--Indentations made by equal weights, in the centre, and near the
edges of the fresh cut ends of the bars, were equal; showing that the
iron was as hard in the centre of the bars as elsewhere.
GENERAL SUMMARY OF THE RESULTS OBTAINED BY SIR WILLIAM FAIRBAIRN'S
EXPERIMENTS.
--+-------------------+-----------+-------------------+------------
| | Breaking | | Strength,
| Condition of bar. | weight of |Breaking weight per| the un-
| |bar in lbs.| square inch. |touched bar
| | | |being unity.
--+-------------------+-----------+-------------------+------------
| | | In lbs. In tons. |
1| Untouched (black) | 50,346 | 58.628 26.173 | 1.000
3| Rolled cold | 69,295 | 88.230 39.388 | 1.505
4| Turned | 47,710 | 60.746 27.119 | 1.036
--+-------------------+-----------+-------------------+------------
NOTE.--In the above summary it will be observed that the effect of
consolidation by the process of cold rolling is to increase the tensile
powers of resistance from 26.17 tons per square inch, to 39.38 tons,
being in the ratio of 1:1.5, one-half increase of strength gained by the
new process of cold rolling.
Extract from the general conclusions arrived at by Professor R. Thurston
from experiments.
"The process of cold rolling produces a very marked change in the
physical properties of the iron thus treated.
"It increases the tenacity from 25 to 40 per cent., and the resistance
to transverse stress from 50 to 80 per cent.
"It elevates the elastic limit under torsional as well as tensile and
transverse stresses, from 80 to 125 per cent....
"It gives the iron a smooth bright surface, absolutely free from the
scale of black oxide unavoidably left when hot rolled.
"It is made exactly to gauge diameter, and for many purposes requires no
further preparation.
"The cold-rolled metal resists stresses much more uniformly than does
the untreated metal. Irregularities of resistance exhibited by the
latter do not appear in the former; this is more particularly true for
transverse stress.
"This treatment of iron produces a very important improvement in
uniformity of structure, the cold-rolled iron excelling common iron in
density from surface to centre, as well as in its uniformity of strength
from outside to the middle of the bar.
"This great increase of strength, stiffness, elasticity, and resilience
is obtained at the expense of some ductility, which diminishes as the
tenacity increases. The modulus of ultimate resilience of the
cold-rolled iron is, however, above 50 per cent. of that of the
untreated iron.
"Cold-rolled iron thus greatly excels common iron in all cases where the
metal is to sustain maximum loads without permanent set or distortion."
From this it appears that cold-rolled iron is peculiarly adapted for
line shafting. Suppose, for example, a given quantity of power to
transmit, and that a length of cold-rolled and a length of hot-rolled
iron be connected together to form the line. Then the diameters of the
two being such as to have equal torsional strength, we have--
1st. That the weight of the cold rolled will be the least, and it will,
therefore, produce less friction in the hanger bearings.
2nd. That the cold rolled will be harder, and will therefore suffer less
from abrasion of the journals.
3rd. That being of smaller diameter the journals are more easily and
perfectly lubricated.
The resistance to transverse stress (say) 50 per cent.; but the elastic
limit under transverse stress is increased from 80 to 125 per cent.,
accepting the lesser amount we have in the case of the two shafts.
4th. That the resistance to permanent set or bend will be 30 per cent.
more in the cold rolled.
5th. The accuracy to gauge diameter enables the employment of a coupling
having a continuous sleeve, and gives an equal bearing along the entire
coupling bore.
6th. The reduction of shaft diameter enables the employment of a smaller
and lighter coupling; and
7th. The hubs of the pulleys may be made smaller and lighter, are easier
to bore, and may be bored to gauge diameter with the assurance that they
will fit the shaft.
The friction between the journals of a line shafting and its bearings
depends so intimately upon the distance apart of the bearings, upon the
alignment of the same, upon the accurate bedding of the shaft journals
to the bearings, and upon the amount of transverse strain; and this
latter is so influenced by the amount of power that may be delivered
from one side of the shaft more than from another, that the application
of rules for determining the said friction under conditions of perfect
alignment rigidity would be practically useless. The conditions found in
actual practice are so widely divergent and so rarely alike, or even
nearly alike, that the consideration of this part of the subject would,
in the opinion of the author, be of no practical value. The reader,
however, is referred to the remarks made with reference to the friction
of journals.
To prevent end motion to a line of shafting it is necessary that there
be fixed at some part of the line two shoulders, or collars, on
relatively different sides of a bearing, or of the bearings, these
collars meeting the side faces of the bearing. If shoulders are produced
by reducing the diameter of the journal bearing of the shaft, the
strength of the shafting is reduced to that at the reduced bearing,
because the strength of the whole can be no greater than its strength at
the weakest part. If collars are placed one on each end of the line of
shafting, the difficulty is met that the collars will permit end motion
to the shaft whenever the temperature of the shaft is greater than that
which obtained at the time at which the collars were adjusted, which
occurs on account of the increased expansion of the shaft. On the other
hand the collars will bind against the side faces of the bearing boxes
whenever the shaft is at a lower temperature than it was at the time of
setting the shaft, because of the contraction of the shaft's length, and
this would cause undue friction, abrasion, and wear.
It is preferable, therefore, to place such collars one on each side of
one bearing, so that the difference in contraction and expansion from
varying temperatures shall be confined to the difference in expansion
between the metal of which the bearing and shaft respectively are
composed in the length of the bearing only, instead of being extended to
the difference in expansion between the shaft throughout its whole
length and that of the framework to which the hangers, or bearings, are
bolted.
[Illustration: Fig. 2593.]
The collars may be shrunk on to the shaft so as to avoid the necessity
of set-screws, or if set-screws are used they should be as short as is
practicable so as to avoid the liability to catch against the lacings,
&c., of belts, which, on slipping off the pulley may come into contact
with the set-screw head. The Lane and Bodley Co., of Cincinnati, employ
a collar (for loose pulleys, &c.) in which the radius of the collar for
a width equal to the diameter of the set-screw head, is equal to that of
the set-screw head thus projecting from the centre of the collar
circumference, a slot in the ring affording access to the set-screw
head, as shown in Fig. 2593. By this means the head of the set-screw is
protected from contact with a belt, in case the latter should be off the
pulley and resting upon the shaft.
As a rule it is preferable that the collars, to prevent end motion to
the shaft, be placed at the bearing nearest to the engine or motor; and
this is especially desirable where bevel-wheels are employed to drive
the shaft, because in that case the pitch lines of the wheels are kept
to coincide as nearly as practicable, and the teeth are prevented from
getting too far into or out of gear.
DIAMETERS OF LINE SHAFTING.--The necessary diameters of the various
length of the shafts composing a line of shafting, should be
proportioned to the quantity of power delivered by each respective
length, and in this connection the position of the various pulleys upon
the length and the amount of power given off by the pulley is an
important consideration. Suppose, for example, that a piece of shafting
delivers a certain amount of power, then it is obvious that the shaft
will deflect or bend less if the pulley transmitting that power be
placed close to a hanger or bearing than if it be placed midway between
the two hangers or bearings.
The strength of a shaft to resist torsion is the cube of its diameter in
inches, multiplied by the strength of the material of which the shaft is
composed, per square inch of cross-sectional area, giving the strength
in statical foot-pounds. The application of this rule is to find the
necessary strength of the shaft to convey power irrespective of the
distance from its centre at which it delivers such power.
But since the point at which the power to produce torsion is applied is
at the rim of the pulley, the amount of torsion produced upon a shaft by
a given stress must be obtained by multiplying the given amount of
stress by the radius of the pulley in inches and parts of an inch.
Example: the static stress upon a pulley, 24 inches diameter, is 100
lbs., what static torsion does it exert upon the shaft?
Here, stress 100 × 12 (radius of the pulley) = 1200 = static torsional
stress.
In the following rules for finding the necessary diameters and strengths
of shafts, the margin of extra diameter for strength necessary for
safety is included, so that the given sizes are working diameters.
To find the necessary diameter of shaft from a given torsional
stress.--Rule, divide the torsional stress expressed in statical foot
lbs., by 57.2 for steel, by 27.7 for wrought iron, or by 18.5 for cast
iron, and the cube root of the quotient is the required working diameter
of shaft expressed in inches.
To find the maximum amount of horse-power capable, within good working
limits, of being transmitted by a _shaft_ of a given diameter.--Rule,
multiply the cube of the diameter of the shaft, in inches, by its
revolutions per minute and divide by 92 for steel, by 190 for
wrought-iron, or by 285 for cast-iron shafts, and the quotient is the
amount of horse-power.
Since, in this rule, the horse-power is a given quantity, the diameter
of the pulley is of no consequence, since with a given stress it must
have been taken into account in obtaining the horse-power.
To find the revolutions per minute a shaft will require to make to
transmit a given amount of horse-power.--Rule, multiply the given amount
of horse-power by 92 for steel, by 190 for wrought-iron, or by 285 for
cast-iron shafts, and divide the product by the cube of the diameter of
the shaft expressed in inches, and the quotient is the required
revolutions per minute for the shaft.
The rule adopted by William Sellers and Co. to determine the size of
shafts to transmit a given horse-power is:--Rule, divide the cube root
of the horse-power by the revolutions per minute and multiply the
quotient by 125, the product is the diameter of shaft required.
This gives a shaft strong enough to resist flexure, if the bearings are
not too far apart. The distance apart that the bearings should be placed
is an important consideration. Modern millwrights differ slightly in
opinion in this respect: some construct their mills with beams 9 feet 6
inches apart, and put one hanger under each of the beams; others say 8
feet apart gives a better result. We are clearly of opinion that with 8
feet distance, and shafting lighter in proportion, the best result is
obtained.
The following table (from "Machine Tools," by Wm. Sellers and Co.) gives
the strength of round wrought iron as given by Clark:--
TABLE SHOWING STRENGTH OF ROUND WROUGHT-IRON SHAFTING.
+--------+---------------------------------------------------------+
| | TORSIONAL ACTION. |
| +----------+------------+-----------+----------+----------+
| Dia- | Ultimate | Working | Work for | Horse | Speed in |
| meter | resist- | stress. | one turn | Power at | turns |
| of | ance. | | per | the rate | per |
| shaft. | | | minute. | of one | minute |
| | | | | turn per | for |
| | | | | minute. | one- |
| | | | | | horse |
| | | | | | power. |
+--------+----------+------------+-----------+----------+----------+
| =1= | =2= | =3= | =4= | =5= | =6= |
+--------+----------+------------+-----------+----------+----------+
| Inches.| Stat'l. | Stat'l ft. | Ft. lbs. | H. P. | Turns. |
| |ft. tons. | lbs. | | | |
| 1 | .42 | 27.7 | 174 | .00526 | 190 |
| 1-1/4 | .82 | 54.1 | 340 | .01028 | 97.3 |
| 1-1/2 | 1.42 | 93.5 | 587 | .01779 | 56.2 |
| 1-5/8 | 1.80 | 118.9 | 746 | .02259 | 44.3 |
| 1-3/4 | 2.25 | 148.4 | 932 | .02820 | 35.4 |
| 1-7/8 | 2.77 | 182.6 | 1,147 | .03469 | 28.8 |
| 2 | 3.36 | 221.6 | 1,391 | .04211 | 23.7 |
| 2-1/8 | 4.00 | 265.8 | 1,669 | .05062 | 19.8 |
| 2-1/4 | 4.80 | 315.5 | 1,981 | .05995 | 16.7 |
| 2-3/8 | 5.62 | 371.1 | 2,330 | .07051 | 14.2 |
| 2-1/2 | 6.56 | 432.8 | 2,718 | .08224 | 12.2 |
| 2-3/4 | 8.73 | 576.1 | 3,618 | .1094 | 9.14 |
| 3 | 11.3 | 747.9 | 4,697 | .1421 | 7.04 |
| 3-1/4 | 14.4 | 951.0 | 5,972 | .1807 | 5.54 |
| 3-1/2 | 18.0 | 1,188 | 7,458 | .2257 | 4.43 |
| 3-3/4 | 22.1 | 1,461 | 9,173 | .2775 | 3.60 |
| 4 | 26.9 | 1,773 | 11,136 | .3368 | 2.97 |
| 4-1/4 | 32.2 | 2,127 | 13,345 | .4040 | 2.48 |
| 4-1/2 | 38.2 | 2,524 | 15,851 | .4796 | 2.09 |
| 4-3/4 | 45.0 | 2,969 | 18,635 | .5642 | 1.77 |
| 5 | 52.5 | 3,463 | 21,750 | .6579 | 1.52 |
| 5-1/4 | 60.7 | 4,008 | 25,177 | .7616 | 1.31 |
| 5-1/2 | 69.8 | 4,609 | 28,936 | .8758 | 1.14 |
| 5-3/4 | 79.8 | 5,266 | 33,077 | 1.000 | 1.00 |
| 6 | 90.6 | 5,983 | 37,584 | 1.137 | .880 |
| 6-1/2 | 117 | 7,606 | 47,780 | 1.445 | .692 |
| 7 | 144 | 9,501 | 59,682 | 1.805 | .554 |
| 7-1/2 | 177 | 11,680 | 73,254 | 2.220 | .450 |
| 8 | 215 | 14,180 | 89,088 | 2.694 | .371 |
| 8-1/2 | 258 | 17,010 | 106,836 | 3.232 | .309 |
| 9 | 306 | 20,190 | 126,846 | 3.837 | .261 |
| 9-1/2 | 360 | 23,750 | 149,118 | 4.512 | .222 |
| 10 | 420 | 27,700 | 174,000 | 5.260 | .190 |
| 11 | 559 | 36,870 | 231,594 | 7.005 | .143 |
| 12 | 725 | 47,860 | 300,672 | 9.095 | .110 |
| 13 | 922 | 60,860 | 382,278 | 11.83 | .0865 |
| 14 | 1,152 | 76,010 | 477,456 | 14.44 | .0693 |
| 15 | 1,417 | 93,490 | 587,250 | 17.76 | .0563 |
| 16 | 1,720 | 113,500 | 712,704 | 21.56 | .0464 |
| 17 | 2,062 | 136,100 | 854,862 | 25.86 | .0387 |
| 18 | 2,447 | 161,500 | 1,014,768 | 30.69 | .0326 |
| 19 | 2,880 | 190,000 | 1,193,466 | 36.10 | .0277 |
| 20 | 3,360 | 221,600 | 1,392,000 | 42.11 | .0237 |
| |
| NOTE.--To find the corresponding values for shafts of cast iron |
| or steel, multiply the tabular values by the following |
| multipliers: |
| |
| Cast | | | | | |
| iron | 2/5 | 2/3 | 2/3 | 2/3 | 1.5 |
| Steel | 1.2 | 2.06 | 2.06 | 2.06 | .48 |
+--------+----------+------------+-----------+----------+----------+
+--------+---------------------------+
| | TRANSVERSE ACTION. |
| +-----------------+---------+
| | Under | Under |
| | the gross | the net |
| | distributed |weight of|
| Dia- | weight. | shaft. |
| meter |-----------------+---------+
| of |Distance| Gross |Distance |
| shaft. |of bear-| weight |of bear- |
| |ings for| for |ings for |
| | the | the | the |
| |limiting| span. |limiting |
| |deflec- | |deflec- |
| | tion. | | tion. |
+--------+--------+--------+---------+
| =1= | =7= | =8= | =9= |
+--------+--------+--------+---------+
| Inches.| Feet. | Lbs. | Feet. |
| | | | |
| 1 | 6.6 | 30 | 7.9 |
| 1-1/4 | 7.7 | 55 | 9.2 |
| 1-1/2 | 8.6 | 89 | 10.3 |
| 1-5/8 | 9.2 | 112 | 11.0 |
| 1-3/4 | 9.6 | 134 | 11.5 |
| 1-7/8 | 10.1 | 163 | 12.1 |
| 2 | 10.5 | 193 | 12.7 |
| 2-1/8 | 11.0 | 227 | 13.2 |
| 2-1/4 | 11.4 | 264 | 13.7 |
| 2-3/8 | 11.8 | 305 | 14.2 |
| 2-1/2 | 12.5 | 359 | 15.0 |
| 2-3/4 | 13.0 | 450 | 15.6 |
| 3 | 13.7 | 566 | 16.5 |
| 3-1/4 | 14.5 | 701 | 17.4 |
| 3-1/2 | 15.2 | 854 | 18.3 |
| 3-3/4 | 16.0 | 1,029 | 19.2 |
| 4 | 16.7 | 1,225 | 20.1 |
| 4-1/4 | 17.4 | 1,439 | 20.9 |
| 4-1/2 | 18.1 | 1,679 | 21.7 |
| 4-3/4 | 18.8 | 1,943 | 22.6 |
| 5 | 19.4 | 2,220 | 23.3 |
| 5-1/4 | 20.0 | 2,525 | 24.0 |
| 5-1/2 | 20.6 | 2,854 | 24.7 |
| 5-3/4 | 21.2 | 3,210 | 25.4 |
| 6 | 21.6 | 3,600 | 26.2 |
| 6-1/2 | 22.9 | 4,421 | 27.5 |
| 7 | 24.2 | 5,426 | 29.0 |
| 7-1/2 | 25.3 | 6,518 | 30.4 |
| 8 | 26.5 | 7,774 | 31.8 |
| 8-1/2 | 27.6 | 9,133 | 33.1 |
| 9 | 28.7 | 10,650 | 34.4 |
| 9-1/2 | 29.8 | 12,320 | 35.7 |
| 10 | 30.8 | 14,100 | 36.9 |
| 11 | 32.8 | 18,180 | 39.4 |
| 12 | 34.7 | 22,880 | 41.7 |
| 13 | 36.6 | 28,330 | 44.0 |
| 14 | 38.5 | 34,560 | 46.2 |
| 15 | 40.3 | 41,530 | 48.4 |
| 16 | 42.1 | 49,330 | 50.5 |
| 17 | 43.3 | 57,970 | 52.6 |
| 18 | 45.5 | 67,490 | 54.6 |
| 19 | 47.2 | 78,040 | 56.6 |
| 20 | 48.8 | 80,660 | 58.5 |
| |
| NOTE.--To find the corresponding |
| values for shafts of cast iron or |
| steel, multiply the tabular values |
| by the following multipliers: |
| |
| Cast | | | |
| iron | .86 | .81 | .86 |
| Steel | 1.05 | 1.07 | 1.05 |
+--------+--------+--------+---------+
"It is advantageous that the diameter of line shaft be kept as small as
is possible with due regard to the duty, so as to avoid extra weight in
the shafting hangers, pulley hubs and couplings, whose weights
necessarily increase with the diameter of the shafting.
"SPEEDS FOR SHAFTING.--The speed at which shafting should run is
determined within certain limits by the kind of machinery it is employed
to drive. Shafting to drive wood-working machines may, for example, be
made to rotate much faster than that employed to run metal-cutting
machines, because the motions in the wood-working machines themselves
are faster than those in metal-cutting machines. In a general sense, the
rotation of shafting is greater in proportion as the movements of the
machines driven require to run faster.
"This occurs because in proportion as the driving pulleys of the
machines require to rotate faster than the line shaft, the diameters of
the pulleys on the line shaft must be larger than the diameters of those
on the machines; hence a great variation in speed would demand a
corresponding increase of diameter of pulley on the line shaft, and the
extra weight of this pulley would be so much added to the weight causing
friction, as well as so much added to the cost. If small pulleys were
used and countershafts employed to multiply the speed the cost would be
increased, extra room would be taken up; indeed, this is so obvious as
to require no discussion, further than to remark that the faster the
shafting rotates the smaller may be its diameter to transmit a given
horse-power. From deflection and weakness to resist transverse strains
and other obvious causes it is not found in practice desirable to employ
line shafts of less than about 1-1/4 inches in diameter, and the
diameters of shafting employed are usually arrived at from a calculated
speed of about 120 revolutions per minute for metal-cutting machines
such as used in machine shops, 250 revolutions per minute for
wood-working machines, and from 300 to 400 revolutions per minute for
cotton and woollen mills, and the countershafts for the machines usually
have pulleys of the requisite diameters to convert this speed of
rotation into that required to run each respective machine. Tubular or
hollow shafting has been made to run at 600 revolutions per minute, but
this kind of shafting has been of very limited application because of
its expensiveness.
"It is obvious that since the speed of a line shaft is used as a
multiplier in the calculation of the horse-powers of shafts, a given
diameter of shaft will transmit more power in proportion as its speed is
increased. Thus a shaft capable of transmitting 20 horse-power when
making 120 revolutions per minute will transmit 40 horse-power if making
240 revolutions per minute.
"There are now running in some factories lines of shafting 1,000 feet
long each. The power is generally applied to the shaft in the centre of
the mill and the line extended each way from this. The head shaft being,
say, 5 inches in diameter, the shafts extending each way are made
smaller in proportion to the rate of distribution, so that from 5 inches
they often taper down to 1-3/4.
"When very long lines of shafting are constructed of small or
comparatively small diameter, such lines are liable to some
irregularities in speed, owing to the torsion or twisting of the shaft
as power is taken from it in more or less irregular manner. Shafts
driving looms may at one time be under the strain of driving all the
looms belted from them, but as some looms are stopped the strain on the
shaft becomes relaxed, and the torsional strain drives some part of the
line ahead, and again retards it when the looms are started up. This
irregularity is in some cases a matter of serious consideration, as in
the instance of driving weaving machinery. The looms are provided with
delicate stop motion, whereby the breaking of a thread knocks off the
belt shifter and stops the loom. An irregular driving motion is apt to
cause the looms to knock off, as it is called, and hence the stopping of
one or more may cause others near to them to stop also. This may in a
measure be arrested by providing fly-wheels at intervals on the line
shaft, so heavy in their rim as to act as a constant retardant and
storer of power, which power is given back upon any reaction on the
shaft, and thus the strain is equalized. We mention this, as at the
present time it is occupying the thoughts of prominent millwrights, and
the relative advantage and disadvantage of light and heavy fly-wheels
are being discussed, and is influencing the proportions of shafting in
mill construction.[36]"
[36] From "Machine Tools," by William Sellers and Co.
Countershafts are separate sections of shafting (usually a short
section) employed to increase or diminish belt speed, to alter the
direction of belt motion, to carry a loose as well as a fast pulley (so
that by moving the belt on to the loose pulley it may cease to
communicate motion to the machine driven), and for all these purposes
combined.
[Illustration: Fig. 2594.]
[Illustration: Fig. 2595.]
An excellent form of countershaft hanger is shown in Fig. 2594, the
guide for the slide being adjustable along the arm, and fixed in its
adjusted position by means of the set-screws. The bearing is
self-adjusting horizontally for alignment. The countershaft is shown in
Fig. 2595, _a_ _b_ being the bearings, _c_ the cone pulley, _d_ the fast
and _e_ the loose pulley, which is placed next to the bearing, so that
it may be oiled without having to reach past the belt and fast pulley.
By reducing the journal for the loose pulley no collar is needed, the
shaft shoulder and the face of the bearing serving instead.
[Illustration: Fig. 2596.]
When the direction of rotation of the cone pulley on the countershaft
requires to be occasionally reversed, there are two belts, an open one
and a crossed one, from the line shaft to the countershaft, and there
are three pulleys on the countershaft, their arrangement being as shown
in Fig. 2596. L L´ are two loose pulleys, one receiving the open and the
other the crossed belt, both these pulleys being a little more than
twice the width of the belt; F is a fast pulley. By operating the belt
skipper or shifter in the requisite direction either the open or the
crossed belt is brought upon the fast pulley, the other belt merely
moving across the width of its loose pulley, which must be twice that of
the fast one. In the position of the belt shifter shown in the cut, both
belts would be upon the loose pulleys L L´, hence the countershaft would
remain at rest. If the direction of rotation of one pulley is required
to be quicker than the other, two fast pulleys, each slightly more than
twice the width of the belt, may be placed upon the line shaft, one of
them being of enlarged diameter, to give the requisite increased
velocity.
[Illustration: Fig. 2597.]
In Fig. 2597 Pratt's patent friction clutch is shown applied to a
countershaft requiring to rotate in both directions, but quicker in one
direction than in the other; hence, one of the pulleys is of smaller
diameter than the other. The pulleys are free to rotate upon the
countershaft unless engaged by the clutch, which is constructed as
follows:--
The inside surface of the pulley rim is bored and the end surface of the
shoes is turned to correspond. The shoes are in the form of a bell
crank, upon the exposed end of which is provided a small lug, clearly
shown in the cut. To prevent end motion of the pulley a collar is placed
on one side of it and secured to the countershaft, while, on the other,
the sleeve to which the shoes are pivoted is also secured to the
countershaft; upon the shaft between the two pulleys there is a sleeve,
having at each end a conical hub. When this sleeve is moved to the
right, its right-hand coned hub passes between the lugs on the exposed
ends of the shoes, forcing these lugs apart and causing the shoes to
grip the bore of the large pulley, which thereupon rotates the shaft
through the medium of the sleeve upon which the shoes are pivoted.
Similarly, if the engaging (and disengaging) sleeve be moved to the left
it will pass between the lugs of the shoes on the left-hand pulley,
which will, therefore, be caused to drive the shaft. In the position
shown in the cut the engaging sleeve is clear of the ends of all the
shoes, hence the pulleys would be caused to rotate (by their belts), but
the shafts, &c., would remain stationary.
In yet another form the inner face of the pulley rim is coned, and in
place of shoes a disk, whose circumference is coned to fit the pulley
rim, is fast upon the shaft. The shaft is provided with a fixed collar,
and from this collar, as a fulcrum, the pulley and disk are (by means of
short levers attached to a sleeve upon the countershaft) brought into
contact, the thrust on the other side of the pulley being sustained by a
conical surface on the sleeve, fitting to a similar cone on the hub of
the pulley. Thus the pulley is gripped between two coned surfaces, one
on each side, and is released by moving the sleeve laterally so as to
relieve the grip, which it does noiselessly.
By this means motion to the shaft is communicated from the pulley
without the sudden shock incidental to the impact of two fixed pieces,
because the grip of the cones is gradual, and a certain amount of slip
may occur until such time as the grip of the surfaces is sufficient to
drive by friction.
[Illustration: Fig. 2598.]
Fig. 2598[37] represents a cone friction clutch pulley. The outer half
is a working fit upon the shaft, but is secured against end motion by
the collar D. The sliding half is coned and covered with leather as
shown at C C, the outer half being coned to correspond. The sliding half
is driven by a feather fast in its bore, and sliding in a feather-way or
spline in the shaft.
[37] From _The American Machinist_.
The driving power of the device is obtained by means of the friction of
the coned surfaces. The less the angle _x_ of the cones the more power
transmitted with a given pressure of the internal to the external cone.
On the other hand, however, this angle may be so little that the
external cone will not release the internal one when the end pressure on
the latter is removed.
The object is, therefore, to so proportion the angle _x_ of the cones
that their friction will be a maximum, while the internal cone may be
moved endwise and unlocked from the external without undue effort or
strain at the moving clutch bar E. If the angle be 30 degrees, the
clutch will release itself when the lateral pressure is removed. If the
angle be 25 degrees the internal cone will require a slight lateral
pressure to release it. If the angle be 20 degrees, the internal cone
cannot be released by end pressure applied by hand.
The transmitting capacity of the clutch depends upon the pressure
applied to maintain the cones in contact, and therefore upon the
leverage of the clutch bar, whose fork end is shown in section at E.
It is desirable that the end pressure be as small as possible, because
of the friction between E and the hub of the sliding half of the pulley.
The hangers which carry the bearing boxes supporting shafting may be
divided into four principal classes:--Those in which the bearing boxes
are permitted to swivel, and to a certain extent to adjust themselves,
to the axial line of the shafting, and having means to adjust the
vertical height of the bolts.
Those in which the bearings are incapable of such adjustments.
Those in which the bearing boxes are supported on each side; and those
in which the bearing is supported on one side only, so that the shafting
may be taken down without disturbing the couplings.
The first named are desirable in that they eliminate to a certain extent
the strains due to the extra journal bearing friction which occurs when
the shafting is sprung out of its true alignment, and obviate to a great
extent the labor involved in fitting the bore of the bearing boxes to
the journals of the shafting, so as to hold the same with its axis in a
straight line, while they permit of vertical movement to attain vertical
alignment.
[Illustration: Fig. 2599.]
Fig. 2599 represents Wm. Sellers & Co.'s ball-and-socket hanger which
has come into extensive use throughout the United States: _a_ represents
the frame of the hanger threaded to receive the cylindrical threaded
plungers _d_ _e_, which therefore by rotation advance or recede
respectively from the centre of the bearing boxes _b_ _c_.
The ends of these plungers are concave, and the top and bottom halves of
the bearing boxes are provided with a spheroidal section fitting into
the concaves of the plungers, so that when the plungers are adjusted to
fit (a working fit) against the boxes, the latter are held in a
ball-and-socket or universal joint, which permits motion in any
direction, the centre of such motion being central to the spherical
concaves on the ends of plungers _e_ _d_.
To adjust the vertical height of the bearings or boxes, it is simply
necessary to rotate the plungers _d_ _e_, in the threaded holes in the
frame. F is simply a dish to catch the lubricating oil after it has
passed through the bearing.
It is obvious that if a shaft be aligned axially true, and held in a box
of this design, the centre of a length of shaft on either side of the
box may be sprung or deflected out of alignment, and that the box will
adjust itself so that its bore will be parallel with the axis of the
shaft thus deflected, hence the friction between the shaft journal and
the bearing box will be at all times a minimum.
This feature of self-adjustment permits of the employment of longer
bearings, which reduces the wear, as well as the friction, and by
providing sufficient bearing and wearing area, enables the bearings to
be composed of cast iron, which is the cheapest as well as the very best
material of which a bearing can be made, provided that its area of bore
is sufficiently large in proportion to the duty, or load, to have a
pressure of not more than about 60 lbs. per square inch of area.
Again, if the alignment of the shaft should require readjustment from
the warping or sinking of beams, as is a very common occurrence where
hangers are fixed to the joists of ceilings, the adjustment is readily
and easily effected by means of the plungers, nor need the boxes be
fitted to the shaft more than to see that when free from the hangers
they bed firmly down until the crowns of their bore have contact with
the shaft. The hangers themselves require no refinement of alignment,
because that may be secured by means of the plungers, and the boxes
require no fitting to the shafts after the hangers are erected.
In hangers in which the self-adjusting ball-and-socket feature is
omitted, the bottom hangers must not only be accurately aligned, but the
boxes must, to avoid friction and undue wear, all be fitted to the
shaft, and the latter must, during such fitting, be tried in the boxes;
the operation, if properly performed, costing far more in labor than is
equivalent to the difference in the first cost of the ball-and-socket
adjustable hangers and those solid or not self-adjustable, especially if
the boxes be long ones, as about, or not less than, three times the
diameter of the shaft, as they should be.
[Illustration: Fig. 2600.]
An external side elevation of this hanger is shown in Fig. 2600, it
being obvious that the hanger is designed for bolting to timbers, or
framing overhead.
[Illustration: Fig. 2601.]
Fig. 2601 represents a hanger of this class. In this the lower part
carrying the bottom bearing is held to the upper by two bolts, as shown,
the object being to enable the same to be placed in position on a line
of shafting without disturbing the pulleys or the couplings. The lower
section with the bottom bearing is removed and again put on after the
hanger is set over the shaft.
[Illustration: Fig. 2602.]
Fig. 2602 represents an open-sided ball-and-socket hanger in which the
plungers can be retired, the bearings removed, and the hanger erected on
an existing line of shafting without removing the pulleys or couplings,
or disturbing the line of shafting.
[Illustration: Fig. 2603.]
When the face of the framing to which the hangers are to be bolted
stands vertical, the hangers are formed as in Fig. 2603, in which the
ball-and-socket or swivelling feature is maintained as before.
Fig. 2604 represents a wall hanger, which is open in front similar to
the hanger shown in Fig. 2602, and for the same purpose.
[Illustration: Fig. 2604.]
The section of shafting receiving power from the engine or prime mover
is usually supported in bearings or pillow blocks. Pillow blocks are
also used for vertical shafts, and in cases where the foundation or
framing is not liable to lose correct horizontal adjustment.
[Illustration: Fig. 2605.]
Fig. 2605 represents a pillow block, in which the ball-and-socket
principle shown in Fig. 2602 is embodied. The bearings have each a ball
section fitting into spherical recesses or cups provided in the body of
the block, and in the cap, so that the bearings are capable of
swivelling as already described with reference to the hanger Fig. 2599.
[Illustration: Fig. 2606.]
[Illustration: Fig. 2607.]
A sectional view of a pillow block having this adjustable feature is
shown in Fig. 2606. To provide increased seating bearing, and also means
of side adjustment to pillow blocks, they are sometimes bolted to base
plates as in Fig. 2607, room being left in the bolt holes to permit of
their being moved and adjusted upon the plate. The adjustment may be
made by means of wedges, as at A, B in Fig. 2607. These base plates are
usually employed when the pillow block is to be held against a wall.
[Illustration: Fig. 2608.]
An inverted pillow block of similar construction, but designed for the
head line (as the length receiving power from the engine or motor is
termed) of the shafting, is shown in Fig. 2608, but an improved form of
the same has plungers so as to effect a vertical adjustment of the
bearings.
[Illustration: Fig. 2609.]
When a pillow block requires to be enveloped by a wall it is provided
with a wall box as shown in Fig. 2609, and within this box is set the
pillow block as shown, space being sometimes left to adjust the pillow
block laterally within the box by means of a wedge as shown.
In cases where the shafting requires to stand off from a wall to allow
room for the pulleys, brackets or knees, such as shown in Fig. 2610, are
employed.
COUPLINGS FOR LINE OR DRIVING SHAFTS.--The couplings for connecting the
ends of line shafts should accomplish the following objects:--
1. To hold the two shaft ends axially true one with the other.
2. To have an equal grip along the entire length of shaft enveloped by
the coupling.
3. To have a fastening or locking device of such a nature that it will
not be liable to work loose from the torsional strains due to the
flexure of the shaft, which is caused by the belts springing or
straining the axial line of shafting out of the straight line.
[Illustration: Fig. 2610.]
4. To be capable of easy application and removal, so as to permit the
erection or disconnection of the lengths of shafting with as little
disarrangement of the hangers and bearings as possible, and to be light,
run true, and be balanced.
To these requirements, however, may be added that, since it is well-nigh
impracticable to obtain lengths of lathe-turned shafting of exactly
equal diameter, couplings for such shafting require to fill the
following further requirements:
5. The piece or pieces gripping the shaft ends must be capable of
concentric and parallel closure along the entire area, enveloping the
end of each shaft, and must do this at each end independently of the
other, and the piece or pieces exerting the closing or compressing
pressure must grip the closing piece or pieces, enveloping the shafting
over the entire area.
[Illustration: Fig. 2611.]
[Illustration: Fig. 2612.]
[Illustration: Fig. 2613.]
If, for example, a sleeve be split at four equidistant parts of its
circumference, and from each end nearly to the middle of its length, as
in Fig. 2611, any pressure that may be applied to its circumference to
cause it to grip the shaft it envelops will cause it to grip the shaft
with greater force at one part than at another, according to the
diameter of the shaft and the location of the external pressure. Thus,
if the pressure be applied equally along the length A B, the weaker end
B will close most readily, while at A the support afforded by the
unsplit section offers a resistance to closure at the ends A of the
split, hence the shaft, even though a working fit to the sleeve bore,
will be gripped with least force at the end A. If the shaft were simply
a close fit, as, say, just movable by hand on the sleeve bore, the form
of the coupling bore would, when compressed upon the shaft, be as shown
in Fig. 2612, the bend on the necks _a_, _b_, _c_, _d_, being magnified
for clearness of illustration. If the compressing piece covered the
compressed sleeve for a lesser distance, the grip would be more uniform,
because there would be a greater length of the sleeve to afford the
curves _a_, _b_, _c_, _d_, as shown in Fig. 2613. The grip may be more
equalised by boring the sleeve of slightly smaller diameter than the
shaft.
[Illustration: Fig. 2614.]
Fig. 2614 represents a sleeve carrying out this principle. It is
composed of two halves, as shown, bored slightly smaller than the shaft
diameter, and is to be compressed on the shaft, which, acting as a
wedge, would spring open the sides of the bore until the crown of the
bore bedded against the shaft. This, in the case of parallel shaft ends
of equal diameter, would hold them with great force axially true, and
with equal force and bearing, thus meeting all the requirements. If,
however, the end of one shaft were of larger diameter than the end of
the other (as has hitherto been supposed to be the case), the end
accomplished by boring the sleeve of smaller diameter than the shaft is,
that the end of the sleeve is afforded the extra elasticity due to the
transverse spring of the sleeve, which permits the edges of each half of
the sleeve to bear along a greater length of the shaft end than would
otherwise be the case; but the bearing is in this case mainly at and
near the edges of the split.
It will be perceived, then, that under this principle of construction,
when applied to shaft ends of varying diameters, the metal is left to
spring and conform itself to the shape of the parts to be connected, and
that there is nothing outside of the condition of relative diameter of
shaft to sleeve bore to determine what the direction of the spring or
closure of sleeve shall be; but, on the other hand, the principle
possesses excellence in that the sleeve being cylindrical and its
closure taking place equally at similar points of contact the shafts
will be held axially true, one with the other; or in other words, the
movements of the metal while sleeve closure is progressing are equally
radial to the axis of the sleeve, and there is no element tending to
throw the shaft axis out of line one with the other.
If a sleeve have a single split, the manner in which it will grip a
shaft smaller than the sleeve's bore depends upon the manner in which
the compression is effected.
In Fig. 2615, for example, is a ring supposed to be compressed by a
pressure applied at A and at B, causing the ring to assume the form
shown by the dotted lines. The centre of the ring bore would therefore
be moved from C to D. Now, suppose that the end of one section of
shafting were to fit the sleeve bore, then compressing the sleeve upon
it would not practically move the centre of the bore; but if the shaft
at the other end of the sleeve were smaller than the sleeve bore, the
compression of the sleeve to grip the shaft would move the centre of the
bore, and, therefore, of the shaft towards D, hence the axial lines of
the shafts would not be held true one with the other. To accomplish this
latter object, the compression must be equal all round the sleeve, or it
may be applied at the points E and F, Fig. 2616, although it is better
to have the compression area embrace all the circumferential area
possible of the sleeve, and to have the movement that effects the
compression simultaneous and equal at all points on the circumference of
the ring or sleeve, because if these movements are independent, more
movement or compression may be given at one point than at another, and
this alters the centre of the bore; thus, if more pressure were exerted
at E than at F, in figure, the centre of the bore would be thrown
towards F, or _vice versâ_. If the pressure be concentric, the single
split ring or sleeve grips the shaft all round its circumference; hence
it is only necessary in this case to maintain the circumference of the
sleeve in line to insure that the shaft ends be held axially true one
with the other; and if the pressure on the ring be applied equally from
end to end its closure will also be parallel and equal, and the shaft
will be held with equal force along that part of its length enveloped by
the coupling. It is obvious, however, that the piece or sleeve gripping
the end of one shaft must be independent of that gripping the other, so
as to avoid the evils shown in Fig. 2612, while at the same time the
casing or guide enveloping the two independent rings or sleeves must
guide and hold them axially true, one with the other.
[Illustration: Fig. 2615.]
[Illustration: Fig. 2616.]
[Illustration: Fig. 2617.]
In Fig. 2617 is shown an excellent form of _plate coupling_, in which
most of the requirements are obtained. A and B are the ends of the two
lengths of shafting to be connected, C and D are the two halves of the
coupling driven or forced on the ends of the shafting, and further
secured by keys. The end of one half fits into a recess provided on the
other half, so as to act as a guide to keep the shafts axially true one
with the other, and also to keep the two halves true one with the other,
while drilling the holes to receive the bolts E which bolt the coupling
together. The objections to this form are, that it is costly to make,
inasmuch as truth cannot be assured unless each half coupling is fitted
and keyed to the shaft, and turned on the radial or joint faces
afterwards. Furthermore, if the coupling were taken off in order to get
a solid pulley on the shaft, the coupling is apt to be out of true when
put together again, and, therefore, to spring the shaft out of true.
Also, that the bearing, support, or hanger must be open-sided to admit
the shaft, and that each coupling, being fitted and turned to its place,
would be apt to run out of true if removed and applied to another shaft,
whether the same be of equal diameter or not; but if each half coupling
be provided with a feather instead of the usual key, the coupling may be
readily removed and will remain true when put on again.
[Illustration: Fig. 2618.]
Fig. 2618 represents a plate coupling, in which one end of the shaft
passes into the bore of the half coupling on the other length of shaft,
which serves to keep the shafts in line one with the other.
[Illustration: Fig. 2619.]
Fig. 2619 represents a single cone coupling composed of an external
sleeve having a conical bore and a split internal sleeve bored to
receive the shaft, and turned on its outer diameter to the same cone as
the bore of the outer or encasing sleeve. The bolts pass through the
inner sleeve, the bolt head meeting the radial face of the inner sleeve
while the nut meets the radial face of the outer sleeve, so that
screwing up the nut forces the inner sleeve into the outer and closes
the bore of the former upon the shaft. This coupling is open to the
objection that it cannot grip the ends of the shafts equally unless both
shafts be of exactly equal diameter, and the bearing on the smaller
shaft will be mainly at the outer end only, as explained in Fig. 2611.
As a result, the transverse strains on the shaft will cause the
couplings to come loose in time.
[Illustration: Fig. 2620.]
Fig. 2620 represents a coupling composed of a cylindrical sleeve split
longitudinally on one side, as at _d_; the bolts _c_ pass through the
split. Diametrally opposite is another split passing partly through as
at _b_. A key is employed at right angles to the two splits as shown.
Here, again, the pressure on a shaft that is smaller than the other, of
the two shafts coupled, will be mainly at one end, but separation of the
shaft ends is provided against by means of two cylindrical pins on the
ends of the key fitting into corresponding holes drilled in the shaft,
as shown in the side elevation in the figure.
[Illustration: Fig. 2621.]
[Illustration: Fig. 2622.]
In Fig. 2621 is shown a coupling whose parts are shown in Fig. 2622. It
consists of a cylindrical ring turned true on the outside and bored
conical from each end to the middle of its length, as shown. The split
cones are bored to receive the shaft and contain a keyway to receive a
spline provided in the shaft ends, and are turned on the external
diameter to fit the conical borings in the sleeve. Three square bolts
pass through the split cones, which, being square, are prevented from
rotating while their nuts are being screwed up.
To put the coupling together one split cone is passed over the end of
one shaft and the other over that of the other. The sleeve is then put
between the ends of the shaft, the position of the shaft adjusted for
length and the split cones pushed up into the sleeve; the bolts are then
passed through and screwed up. The forcing of the split cones into the
conical borings of the sleeve causes the former (from being split) to
close upon the shaft ends and grip them equally tight, notwithstanding
any slight difference in the diameters of the shaft, there being left
between the ends of the split cones sufficient space to allow them to
pass through the conical borings sufficiently to close upon the
respective ends of the shafts; the pressure being parallel and equal on
each shaft end, because when the cone has gripped the largest shaft the
whole movement due to screwing up the nuts is transferred to the cone
enveloping the smaller shaft, and by reason of the cones fitting, the
closure of the holes in the cones is parallel, giving an even grip along
the shaft end and an equal amount of grip to each shaft end.
To remove the coupling the bolts are removed, and the sleeve being moved
endways the cones open from their spring and relieve the grip upon the
shaft.
It is evident that in their passage through the sleeve casing the cones
will move with their axial lines true with the axial line of the casing;
and it is equally evident that the taper on the cone accurately fitting
the taper in the sleeve bore, the closure of the cone bores must be
equal; while at the same time the pressure on the two cones upon the
respective shaft ends must be equal, because it is the friction of the
cone bores upon the shaft ends which equally resists the motion of both,
while the pressure applied to the respective cones is derived from the
same bolts, and hence is equal and simultaneous in its action.
To loosen this coupling for removal the bolts must be stacked back and a
few blows on the exterior of the outer shell with a billet of wood may
loosen the coupling; but if not, a wedge or a cold chisel may be driven
in the splits of the cones to loosen them, but such wedge or chisel
should not have contact with the sides of the split, either near the
bore or near the perimeter, for fear of raising a burr.
[Illustration: Fig. 2623.]
[Illustration: Fig. 2624.]
In Fig. 2623 is shown a patent internal clamp coupling. It is formed of
a cylindrical piece containing a pair of separate clamps, and between
these clamps and the outer casing are four screws, two to each clamp;
these screws are tapered so as to close the clamp when screwed up and
release it when screwed outwards. The holes to receive the shaft ends
are bored somewhat smaller than the shafts they are to fit, and the
clamps opened to permit the easy insertion of the shaft ends by means of
wedges A driven in the split B of each clamp, as shown in Fig. 2624.
The lower edge of the wedges should be slightly above the bore of the
clamp to prevent the formation of a burr or projection of metal when the
wedge is driven in. When placed upon the shaft ends and in proper
position the wedges are removed and the clamp bore will have contact at
and near the edges of the longitudinal split and on the opposite sides
of the bore where the keyway is shown, but the pressure of the tape
screws will spring the clamps on the side of the longitudinal splits,
and increase the bearing area at those points.
The main features of this device are that though the bore be made a
driving fit to the shaft, it can, by the employment of the wedges, be
put on the shaft with the same ease as if it were an easy fit, while the
clamps being separated by a transverse groove may open and close upon
the shaft independently of each other, so as to conform separately to
any variation in the diameters of the two shaft ends it couples. But it
may be noted that since the circumference of each shaft end has a
bearing along the line of the coupling bore diametrally opposite to the
longitudinal splits, the shafts will not be held quite axially true one
with the other unless there be as much difference in the diameters of
the separate clamp bores as there is in the diameters of the shaft ends;
because to hold two shafts of different diameters axially true one with
the other the longitudinal planes of the two circumferences must not at
any part of the circumferences form a straight line, as would be the
case at that part of the coupling bore at and near the keyway.
It is to be noted, however, that this coupling is formed of one solid
piece, and that the strain on the tightening bolts or screws is one of
compression only, which tends to hold them firmly and prevent their
coming loose.