SHAFTING, PULLEYS, BELTING
AND ROPE TRANSMISSION
THE POWER HANDBOOKS
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BY PROF. AUGUSTUS H. GILL
OF THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY
ENGINE ROOM CHEMISTRY
BY HUBERT E. COLLINS
BOILERS KNOCKS AND KINKS
SHAFT GOVERNORS PUMPS
ERECTING WORK
PIPES AND PIPING SHAFTING, PULLEYS AND
BELTING
BY F. E. MATTHEWS
REFRIGERATION. (In Preparation.)
HILL PUBLISHING COMPANY
505 PEARL STREET, NEW YORK
6 BOUVERIE STREET, LONDON, E. C.
THE POWER HANDBOOKS
Shafting, Pulleys, Belting
AND
Rope Transmission
COMPILED AND WRITTEN
BY
HUBERT E. COLLINS
Published by the
McGraw-Hill Book Company
New York
Successors to the Book Departments of the
McGraw Publishing Company Hill Publishing Company
Publishers of Books for
Electrical World The Engineering and Mining Journal
The Engineering Record Power and The Engineer
Electric Railway Journal American Machinist
_Copyright, 1908_, BY THE HILL PUBLISHING COMPANY
_All rights reserved_
_Hill Publishing Company, New York, U.S.A._
INTRODUCTION
THIS handbook is intended to furnish the reader with practical help
for the every-day handling of shafting, pulleys and belting. These are
allied in the operation of plants and it is a pretty generally conceded
fact that all three are much neglected by many operators.
A close perusal of these pages will enable the reader to determine
the best course to pursue in the most common instances and in various
troubles, and in all articles there are suggestions for similar cases
which may arise.
For instance, the need of belt dressing as a preservative, now
generally conceded by most authorities, is fully covered in Chapter
XI and the result of a test made by disinterested parties to find the
degree of efficiency of four of the best known dressings is given. The
results are of importance to all belt users.
A portion of the book is also given to rope transmission which is in
more general use to-day than ever before, and in this connection some
advice is offered by experts as to the selection and care of the rope.
Rope splices and how to make them will also prove valuable to many
engineers.
The author wishes to make acknowledgment to various contributors
to _Power_ whose articles are used herein, and to some special
contributors, from whose articles small portions have been taken.
Acknowledgment is also made to Stanley H. Moore, the author of
"Mechanical Engineering and Machine Shop Practice" for the section on
splicing.
HUBERT E. COLLINS.
NEW YORK, _November_, 1908.
CONTENTS
CHAP. PAGE
I SHAFTING HINTS 1
II SHAFTING HINTS 21
III SHAFTING HINTS 32
IV TRUING UP LINE SHAFTING 49
V APPARATUS FOR LEVELING AND LINING SHAFTING 54
VI SOME PRACTICAL KINKS 61
VII PRACTICAL METHODS OF LOOSENING PULLEYS 65
VIII SPLICING LEATHER BELTS 72
IX CARE AND MANAGEMENT OF LEATHER BELTS 89
X BELTING--ITS USE AND ABUSE 99
XI A COMPARATIVE TEST OF FOUR BELT DRESSINGS 102
XII BELT CREEP 106
XIII ROPE DRIVES 108
XIV A NEW SCHEME IN ROPE TRANSMISSION 115
XV HOW TO ORDER TRANSMISSION ROPE 122
XVI A BELTING AND PULLEY CHART 129
XVII SPLICING ROPE 135
XVIII WIRE ROPE TRANSMISSION 143
I
SHAFTING HINTS[1]
IN the installation, maintenance and repair of shafting, as in all
other things, there is a right and a wrong way; and though the wrong
way ranges in its defects from matters causing trivial inconvenience
to absolute danger, the right too often--owing to lack of knowledge or
discernment--finds but scant appreciation.
[1] Contributed to Power by Chas. Herrman.
Where, as is often the case, the end of a shaft is journaled to admit
of the use of an odd, small-bore pillow block or wall-box hanger, the
journaled part should equal in length twice the length of the hanger
bearing plus the length of the collar. The hanger can thus readily be
slid out of the wall box, and the necessity of uncoupling this shaft
length and removing it before access to the bearing for purposes of
cleaning or repair is done away with.
A plank or board _A_ (Fig. 1), about 1/4 to 1/2 inch longer than the
distance from the bottom of the shaft to the floor, can be used to good
advantage at such times to free the hanger of the shaft's weight, and
to prevent the shaft's springing from its own weight and the pulleys it
may be carrying.
Should it become necessary to place a pulley with half the hub on and
half off the journaled part, this can readily be done by the use of a
split bushing, as shown in sectional view of Fig. 1.
[Illustration: FIG. 1.]
Very often a small-sized bearing is used and the shaft journaled off
to act as a collar. Of this procedure it can only be said that if done
with the idea of making a "good job" it signally fails of its object;
if of necessity (a collar being insufficient), then the shaft is
heavily overloaded and serious trouble will result, because of it.
It is advisable to center punch, or otherwise mark, the ends of both
shafts held by a compression coupling close up against the coupling,
and both edges of the coupling hub should have a punch mark just
opposite and close to the shaft punch marks. These marks will serve
at all times to show at a moment's glance any end or circumferential
slippage of the shafts within the coupling. The same method can be
resorted to for proof of pulley slippage.
When a new line of shafting is put up, the foot position of each hanger
should be clearly marked out on their respective timbers _after_ the
shaft has been brought into alinement. Hangers can thus be easily
put back into their proper place should timber shrinkage or heavy
strains cause them to shift out of line. This idea can be applied to
good advantage on old lines also, but before marking out the hanger
positions the shaft should be tried and brought into perfect alinement.
Hangers that do not allow of any vertical adjustment should not be used
in old buildings that are liable to settle. Shafting so run pretty
nearly always gets out and keeps out of level.
In flanged bolt couplings (Fig. 1) no part of the bolt should project
beyond the flanges. And where a belt runs in close proximity to such
a coupling, split wood collars should be used to cover in the exposed
coupling flanges, bolt heads and nuts. Countershafts have been torn out
of place times innumerable by belts getting caught and winding up on
the main line.
Whenever possible a space of 8 to 10 inches should be left between the
end of a shaft line and the wall. A solid pulley or a new coupling can
thus readily be put on by simply uncoupling and pushing the two shaft
lengths apart without taking either down. Ten inches does not represent
the full scope of pulleys admissible, for so long as the pulley hub
does not exceed a 10-inch length the pulley face (the more readily in
proportion to the larger pulley diameter) can be edged in between the
shafts.
Fig. 2 is an instance of bad judgment in locating the bearings. In one
case this bearing overheated; the remedy is either to re-babbitt the
old box or replace it with a new one.
Both pulleys were solid and the keys--headless ones--had been driven
home to stay. The rims of both pulleys almost touched the wall, and the
circumferential position on the shaft of both these pulleys was such as
to preclude the possibility (owing to an arm of _a_ being in a direct
line with key _B_^1 and arm of _b_ with key _a_^1) of using anything
but a side offset key starting drift.
[Illustration: FIG. 2.]
An effort was made to loosen _b_ (which was farthest from the wall)
by sledge-driving it toward the wall, hoping that the pulley might
move off the key. The key, as was afterward found out, not having been
oiled when originally driven home had rusted in place badly; though
the pulley was moved by sledging, the key, secure in the pulley hub,
remained there.
Ultimately one of us had to get into pulley _b_, and, removing cap _c_,
hold the improvised side offset, long, starting drift _D_ in place
against _B_^1 at _b_^2 while the other swung the hand sledge at _a_.
The entering end of the key, not having been file chamfered off, as it
should have been (see _E_), our starting drift burred it up; so, after
having started it, we had the pleasure of getting into _b_ to file the
key end _b_^2 into shape so as to admit of getting it out.
The solid pulley _b_ has since been replaced with a split pulley.
By the arrangement, as shown in Fig. 3, of the rim-friction
clutch on the driven main shaft _B_ and the driving pulley on the
engine-connected driving main shaft _A_, no matter whether _B_
shaft is in use or not--_i.e._, whether the clutch be in or out of
engagement--so long as _A_ shaft is in motion the belt _C_ is working.
[Illustration: FIG. 3.]
Main line belts come high, and the more they are used the sooner will
they wear out. By changing the clutch from shaft _B_ to _A_ and the
pulley _D_ from _A_ to _B_, belt _C_ will be at rest whenever _B_ is
not in use. Where, however, these shafts are each in a separate room or
on a different floor (the belt running through the wall or floor and
ceiling, as the case may be) the clutch, despite belt wear, should be
placed directly on the driven shaft (as _B_), so as to provide a ready
means for shutting off the power in cases of emergency.
Figs. 4, 5 and 6 represent a dangerous mode, much in vogue, of driving
an overhead floor. An extremely slack belt connects the driving shaft
_A_ and the driven shaft _B_; when it is desired to impart motion to
the driven shaft the belt tightener _C_ is let down and belt contact is
thus secured.
[Illustration: FIG. 4.]
[Illustration: FIG. 5.]
[Illustration: FIG. 6.]
This tightener system is called dangerous advisedly, for few are
the shops employing it but that some employee has good cause to
remember it. Unlike a clutch--where control of the power is positive,
instantaneous and simple--the tightener cannot be handled, as in
emergency cases it has to be.
In any but straight up and down drives with the driven pulley equal to
or larger (diametrically) than the driver, unless the belt have special
leading idlers there is more or less of a constant belt contact with
its resultant liability to start the driven shaft up unexpectedly. When
the tightener is completely off, the belt, owing to heat, weight or
belt fault, may at any time continue to cling and transmit power for a
short space, despite this fact.
These tighteners are usually pretty heavy--in fact, much heavier than
the unfamiliar imagines when on the spur of emergency he grapples them,
and trouble results.
Tightener (in Fig. 5) _A_ is held in place by two threaded rods _B_--as
shown by slot _a_ in _A_^1--and regulated and tightened by ring-nuts
_C_ working along the threaded portion of _B_. _C_ (of Fig. 4) is also
a poor arrangement. Fig. 6 is the best of them all.
Apropos of clutches, great care must be exercised in tightening them
up while the shafting is in motion, for if the least bit overdone the
clutch may start up or, on being locked for trial (according to the
clutches' structure), continue running without possibility of release
until the main source of power be cut off. Nothing can exceed the
danger of a clutch on a sprung shaft.
Heavily loaded shafting runs to much better advantage when center
driven than when end driven, and what often constitutes an overload
for an end drive is but a full load for a center drive. To illustrate,
here is one case of many: The main shaft--end driven--was so overloaded
that it could be alined and leveled one week and be found out one
way or the other, frequently both ways, the next week. Being tired
of the ceaseless tinkering that the condition under which that shaft
was working necessitated, the proprietors were given the ultimatum: A
heavier line of shafting which would be sure to work, or a try of the
center drive which, owing to the extreme severity of this case, might
or might not work.
[Illustration: FIG. 7.]
[Illustration: FIG. 8.]
A center drive, being the cheapest, was decided upon. Pulley _A_,
Fig. 7, which happened to be a solid, set-screw and key-held pulley,
was removed from the end of the shaft. The split, tight-clamping-fit
pulley _B_, Fig. 8, was put in the middle of the shaft length; the gas
engine was shifted to accommodate the new drive, and hanger _C_^1 was
put up as a reinforcement to hanger _C_ and as a preventive of shaft
springing. After these changes the shaft gave no trouble, so that, as
had been hoped, the torsional strain that had formerly all been at
point 1 must evidently have been divided up between points 2 and 3.
When a main shaft is belted to the engine and to a countershaft,
as shown in Fig. 9, the pulley _A_^1 gets all the load of main and
countershafts. In the arrangement shown in Fig. 10 point 1 gets _A's_
load and 2 gets _B's_ load and is the better arrangement.
[Illustration: FIG. 9.]
[Illustration: FIG. 10.]
Where a machine is situated close to one of the columns or timber
uprights of the building it is very customary to carry the belt shifter
device upon the column, as in Fig. 11. The sudden stoppage of a machine
seldom does any damage, whereas an unexpected starting may cause
irreparable damage and often even endanger the limb and life of the
machine operative.
[Illustration: FIG. 11.]
To avoid the possibility of some passing person brushing up against
the shifting lever and thus starting the machine, the tight and loose
pulleys of the countershaft should be so placed that when _A_ is
exposed--that is, away from the column--its accidental shifting shall
stop the machine. Fig 12 makes this point clear.
[Illustration: FIG. 12.]
This arrangement is often used to save a collar (at _A_). The oil
runs out between the loose pulley and the bearing, especially if the
latter be a split bearing; the loose pulley, instead of being totally
free when the belt is on the tight pulley, acts more or less, in
proportion to the end play of the shaft, as a buffer between the tight
pulley and the bearing; finally, the tight pulley is deprived of the
support (which, when under load, it can use to good advantage) a nearer
proximity to the hanger would give it.
The shafts of light-working counters should not be needlessly marred
with spotting or flats for collar set-screws, nor should cup or pointed
set-screws (which mar a shaft) be used. If the collar be sharply tapped
with a hammer, diametrically opposite the set-screw, while it is being
tightened up, all slack is taken out of the collar; and the hold is
such that, without resource to the same expedient when loosening the
collar, a screwdriver will scarcely avail against a slotted set-screw.
When required to sink the head of a bolt into a timber to admit of the
timbers lying snug in or against some spot, if allowable, the bolt's
future turning can be guarded against by cutting the hole square to
fit the bolt head. But where a washer must be used, the only positive
and practical way to prevent the bolt from turning is to drive a nail
(as shown) into _A_ (Fig. 13) far enough for the nail head to flush
_B_; now bend the head down behind the bolt toward _c_. It is evident
that if the bolt tries to turn in the direction of 3 the nail end
(wood held) will prevent it; if toward 4, the nail head will be forced
against the wood and catch hold of the bolt head.
[Illustration: FIG. 13.]
Large belts of engines, dynamos, motors, etc., when in need of
taking-up are usually attended to when the plant is shut down; that
is, nights, Sundays or legal holidays. At such times power is not to
be had; and if the spliced part of the belt, which must be opened,
shortened, scraped, re-cemented and hammered, happens to be resting
against the face of one of the pulleys, is up between some beams or
down in a pit, the chances of the job, if done at all, being any good
are very slim.
The spliced part of a large belt should be clearly marked in some
permanent and easily recognizable way (a rivet, or where the belt is
rivet-held at all its joints some odd arrangement of rivets is as good
a way as any). This marking will minimize the possibility of mistake
and enable the engineer to place the belt splice in the position most
favorable for the belt-maker's taking-up.
In wire-lacing a belt, very often, despite all efforts and care, the
edges of the belt (_A_, _B_) get out of line, as shown in Fig. 14,
and make the best of jobs look poor. By securing the belt in proper
position by two small pieces of wire passed through and fastened at 1,
2, 3 and 4, Fig. 15, the lacing can be more conveniently accomplished
and the edge projection is avoided. When the lacing has progressed far
enough to necessitate the removal of wires _c_ _d_, the lacing already
in place will keep the belt in its original position.
[Illustration: FIG. 14.]
[Illustration: FIG. 15.]
A wire lacing under certain conditions will run a certain length of
time to a day. On expensive machinery whose time really is money it
pays to renew the lacing at regular intervals so as to avoid the loss
of time occasioned by a sudden giving out of the lace.
Never throw a belt on to a rim-friction or other kind of clutch while
the shaft is in full motion. Belts, when being thrown on, have a knack,
peculiarly their own, of jumping off on the other side of the pulley.
And should a belt jump over and off on the wrong side and get caught
in the clutch mechanism, as the saying goes, "there will be something
doing" and the show usually comes high. It pays to slow down.
A mule belt (transmitting in the neighborhood of or considerably over
25 horse-power) that runs amuck through the breaking down of the mule
can make enough trouble in a short time to keep the most able repairing
for a long while.
[Illustration: FIG. 16.]
No matter what the pulley shafts holding arrangement and adjusting
contrivance may be, all of the strain due to belt weight, tension, and
the power transmitted falls mainly at points _A_, _A_^1, Fig. 16; and
it is here that, sooner or later, a pin, set-screw or bolt gives way
and the belt either gets badly torn up, rips something out of place,
or a fold of it sweeping to the floor slams things around generally
until the power is shut off.
The remedy is obvious: Reinforce _A_, _A'_ by securing _B_, _B'_ to
the supporting shaft _c_ at _c_^1, _c_^2. The yoke _x_ is a reliable
and practical means to this end. Straps _a_ held by the nuts _b_ hold
the yoke securely on the supporting shaft _c_, while the pulley-shaft
ends _B_, _B'_ are held in the _U_ of the yoke at _w'_ at any desired
distance from _c_ by means of the adjustment provided by the nuts _b_.
[Illustration: FIG. 17.]
The end of a hanger bearing was badly worn (Fig. 17). The cap could
be lifted out by removing bridge _A_, but the shaft interfered with
the lifting of the bottom out, owing to its being held in the hanger
slides. It had to be removed and we were called upon to put it into
shape by re-babbitting.
Being a newspaper plant, money was no object; the time limit, however,
was three hours, or hands off. Opening the 30-inch engine belt and
removing the interfering shaft length was out of the question in so
short a time. So the job was done as follows: The shaft was braced
against down sag and engine pull along the line _B_ _C_ by a piece of
timber at _A_, and against pull on _B_ _D_ by timber arrangement _X_;
timber _y_'s points _y_^1 and _y_^2 resting against the uprights at 1
and 2, timber _z_ wedged in between _y_ at _y_^3 and the shaft at 4,
thus acting as the stay along line _B_ _D_. The nuts and washers _a_,
_a_ were removed; the bolts driven back out of the bracket; the end
of a rope was thrown over the shaft at _b_, passed through the pulley
and tied to the bracket and hanger which, as one piece, were then
slid endways off the shaft and lowered to the floor. The bearing was
cleaned, re-babbitted and scraped, everything put back, stays removed
and the shaft running on time with a half-hour to the good.
[Illustration: TIMBER ARRANGEMENT X]
When desirable to keep a shaft from turning while chipping and filing
flats, spotting in set screws or moving pulleys on it, it can be done
by inserting a _narrow_ strip of cardboard, soft wood or several
thicknesses of paper between the bearing cap and the top of the shaft
and then tightening the cap down.
The packing, 1-16 to 3-16 inch thick and about as long as the bearing,
must be narrow; otherwise, as may be deduced from Fig. 18 (which shows
the right way), by the use of a wide strip in the cap the shaft is
turned into a wedge, endangering the safety of the cap when forced
down. At point 3 packing does no harm, but at 1 and 2 there is just
enough space to allow the shaft diameter to fit exactly, with no room
to spare, into the cap bore diameter.
[Illustration: FIG. 18.]
As a very little clamping will do a good deal of holding the clamping
need not be overdone. A shaft can also be held from turning, or turned
as may be desired, by holding it with a screw (monkey) wrench at any
flat or keyway, as shown in sectional view, Fig. 19.
When a shaft breaks it is either owing to torsional strain caused by
overload, springing through lack of hanger support at the proper
interval of shaft length, the strain of imperfect alinement or level,
or a flaw.
An immediate temporary repair may be effected by taking some split
pulley that can best be spared from another part of the shaft and
clamping it over the broken part of the shaft, thus converting it, as
it were, into a compression coupling. The longer the pulley hub the
better the hold; spotting the set-screws--that is, chipping out about
1/8-inch holes for their accommodation into the shaft--is also a great
help.
[Illustration: FIG. 19.]
If when the shaft breaks it has not been sprung by the sudden dropping
of itself and the pulleys that were on it, a permanent repair can be
effected, after correcting the cause of the break, by the use of a
regular key-less compression coupling.
If it has been sprung, a new length comes cheapest in the wind-up; and
if overload was the original cause of the trouble, only a heavier shaft
or a considerable lightening of the load will prevent a repetition.
In Fig. 20 _A_ shows how to drive to make belt weight count in securing
extra contact. In _B_ this weight causes a loss of contact. Bearing
in mind that _B_ is not only a loss from the normal contact but
also a loss of the extra contact that _A_ gives, it will readily be
seen how important a power-saving factor the right sort of a drive
is--especially on high-speed small-pulley machines, such as dynamos,
motors, fans, blowers, etc.
[Illustration: FIG. 20.]
A good many electrical concerns mount some of their styles of dynamos
and motors (especially the light duty, small size) upon two _V_-shaped
rails, Fig. 21 (the bottom of the motor or dynamo base being V-grooved
for the purpose). The machine's weight and the screws _A_ are counted
on to keep it in place. If the machine be properly mounted on these
rails, as regards screws _A_ in relation to its drive, the screws
reinforce the machine's weight in holding it down and also permit a
surer adjustment through this steady holding of the machine.
[Illustration: FIG. 21.]
Fig. 22 shows the machine properly mounted. The belt tension and pull
tend to draw _B_ corner of the machine toward the shaft _C_; and screw
_B_^1 is there to resist this pull. Owing to this resistance and
the pull along line _D_, _E_ tends to lift and slew around in _E_^1
direction; screw _E_^2 is, however, in a position to overcome both
these tendencies. If the screws are both in front, there is nothing
but the machine's weight to keep the back of it from tilting up. The
absurdity of placing the screws at _F_ and _G_, though even this is
thoughtlessly done, needs no demonstration.
[Illustration: FIG. 22.]
When putting a new belt on a motor or dynamo, both the driver and the
driven are often needlessly strained by the use of belt-clamps, in the
attempt to take as much stretch out of the belt as possible. On being
loosely endlessed it soon requires taking up; and if only laced, when
the time for endlessing comes the belt is botched by the splicing in
of the piece which, owing to the insufficiency of the original belt
length, must now be added to supply enough belt to go around, plus the
splice.
The proper mode of procedure is: Place the motor on its rails or slides
5 inches away from its nearest possible approach to the driven shaft
or machine and wire-lace it (wire-lacing is a very close second to an
endless belt). Let it run for a few days, moving the motor back from
the driven shaft as the belt stretches. When all reasonable stretch is
out, move the motor back as close to the driven shaft as possible.
The 5 inches forward motion will give 10 inches of belting, which will
be amply sufficient for a good splice; and, further, the machine will
be in position to allow of tightening the belt up, by simply forcing
the motor back, for probably the belt's lifetime.
II
SHAFTING HINTS[2]
THE bolts, set-screws, pulleys, bearings, shafting and clutches of
a plant, although among the foremost factors in its efficiency, are
very often neglected until they reach the stage where their condition
absolutely compels attention.
[2] Contributed to Power by Chas. Herrman.
Very often this lack of proper attention is due to surrounding
difficulties of an almost insurmountable and most discouraging nature.
At other times it is due to a lack of proper appreciation of the damage
resultant from seemingly insignificant neglects. How to overcome some
of these difficulties is the object of this chapter.
Fig. 23 shows a case of a turning bolt. The head is inaccessible and
the bolt's turning with the nut, owing to burrs or rust, prevents
either the tightening or the loosening of the nut. One to three
fair-sized nails driven through the timber as at _C_, hard up against,
or, better still, forced into a tangent with the bolt, will often
suffice to hold it while the nut is being turned. In iron girders,
beams, etc., the nail method being impossible, a slot _E_ can easily be
cut with a hack-saw through the lower end of both the nut and bolt, so
that the bolt may be held by a screwdriver while the nut is turned with
a wrench.
Where an extra strong screwdriver must be used, the use of two blades
at the same time in the hack-saw frame will give a slot of the
requisite width. Where the bolt's end projects beyond the nut and it
is desired to tighten the nut, a Stillson wrench is often, though
inadvisedly, called into service. This tends to spoil the lower threads
of the bolt and thus prevents any future loosening, except by the
cutting off of the projecting end.
[Illustration: FIG. 23.]
As the alinement and level of shafting depend on the power of their
hold, bolts, lag-bolts and set-screws should, when they are tightened,
be so in fact and not in fancy.
The proper way to use a wrench, especially a screw wrench, so as to
avail yourself of every ounce of power, not of your biceps only but
of your whole body, is as follows: Place your shoulders on a level
with the object to be tightened, secure the wrench jaws well upon it,
grasp the jaws with the left hand and the wrench handle with the right,
holding both arms straight and tense; swing the upper part of the body
to the right from the hip, backing the force of your swing up with
the full force of your legs, steadying yourself the while with your
left-hand grip on the wrench jaws, which are the center of your swing.
Several such half turns, at the wind-up, will cause an extremely hard
jam with comparative ease.
In tightening up a split-pulley, the expedient of hammering the bolts
tight, by means of an open-ended bolt-wrench and a small sledge, is
often resorted to. If the head of the bolt be lightly tapped while the
nut is being tightened, even a light hammering, except in the extremest
cases, becomes unnecessary.
Split-pulleys are invariably better held in place by a good clamping
fit than by set-screws. It must also be borne in mind that, for good
holding, set-screws must be spotted into the shaft, and this defaces
and often materially weakens the shaft. Split-pulleys, like solid
ones, are sometimes subject to stoppage, owing to excessive strain.
Set-screws, at such times, cut a shaft up pretty badly; whereas, if
clamped, only a few slight scratches would result.
Where packing with paper, cardboard, emery cloth or tin becomes
necessary to secure a good clamping fit, care should be taken to put an
equal thickness of packing into both halves of the pulley; otherwise it
will wabble and jump when running.
Emery cloth, on account of its grittiness, is preferable for packing
where the duty done by the pulley is light. When the duty done is
extra heavy, emery cloth, despite its grittiness, will not do; tin or
sheet iron, owing to body, must be used.
The following is the most practical way of packing a split-pulley to a
good clamping fit, assuming that emery cloth is to be used:
The thickness of the emery cloth to be used, and whether to use one
or more folds, can readily be ascertained by calipering the shaft
diameter and pulley bore, or by trial-clamping the pulley by hand. In
both of these instances, however, due allowance must be made for the
compressiveness of the packing used. If the packing be too thin, the
pulley will not clamp strongly enough; if too thick, the chances of
breaking the lugs when drawing the bolts up are to be apprehended.
Having determined the proper thickness of emery cloth to be used, place
the pulley on the shaft, as shown in Fig. 24. Into the lower half _C_,
in space _A_, which is out of contact with the shaft, place a sheet of
emery with the emery side toward the hub and the smooth side toward the
shaft. The width of the emery should be a little less than half of the
shaft's circumference, and it should be long enough to project about
one-half of an inch to an inch on each side of the hub.
Now turn the pulley on the shaft so that the position of the halves
shall become reversed (Fig. 25), _C_ on top, _B_ on bottom. See that
the emery cloth remains in its proper position in half-hub, the smooth
side being toward the shaft; the projecting length beyond the pulley
hub will help you to do this.
Into half-hub _B_ (space _D_) insert a similar sized piece of emery
cloth, smooth side toward the hub and the emery side toward the shaft.
Draw up on your bolts to clamp the pulley into position. Be sure,
however, that no emery cloth gets in between the half-hubs or lugs at
points 1 and 2, Fig. 25, as this would prevent their coming properly
together; the width of the emery being less than half of the shaft's
circumference will be a help to this end.
[Illustration: FIG. 24.]
It often happens, owing to downright neglect or unwitting neglect,
through the oil hole or oiler being blocked up, that a loose pulley,
running unlubricated, cuts, heats, and finally, through heat expansion,
seizes. It then becomes necessary to take the countershaft down, force
the loose pulley off and file and polish the shaft up before it can be
put back into place.
[Illustration: FIG. 25.]
The following method avoids the taking down and putting back, provides
an easy means for loosening up the pulley that has seized, and
improvises, as it were, a lathe for filing and polishing the shaft.
[Illustration: FIG. 26.]
In Fig. 26, _A_ is the loose pulley that has seized. Throw off both
the belt that leads from the main shaft to pulleys _A_, _B_ and the
belt that leads to the driven machine from the driving pulley _C_.
Tie, or get somebody to hold, an iron bar in pulley _A_ at side _a_,
as shown in Fig. 27, over an arm of the pulley, under the shaft, and
resting against the timber, ceiling, wall or floor, in such a way as
to prevent the pulley from turning in one direction, as shown in Fig.
27. Now, with another bar, of a sufficient length to give you a good
leverage, take the grip under a pulley arm and over the shaft in the
tight pulley _B_ at _b_, which will enable you to work against the
resistance of the bar in the loose pulley _A_.
[Illustration: FIG. 27.]
With enough leverage, this kind of persuasion will loosen the worst
of cases. Take the bars out and move _B_ sufficiently to the right
to allow _A_ to take _B_'s former position. Secure _B_ by means of
its set-screws in its new position and, by means of a piece of cord,
fasten an arm of _A_ to one of _B_'s. It is evident that by throwing
the main-shaft belt on to _A_ it will, through _A_'s cord connection
with _B_, which is screwed to the shaft, cause the shaft to revolve,
thus enabling you to file up and polish that portion of it formerly
occupied by _A_. To prevent the countershaft from side-slipping out
of hanger-bearing _D_^1, get somebody to hold something against
hanger-bearing _D_^2 at _E_; or fasten a piece of wire or cord on
the countershaft at _F_ and the hanger _D_^1, so as to prevent
side-slipping while not interfering with revolution.
Filing, polishing, a cleaning out of the oil hole or oiler, and the
taking of proper precaution against future failure of lubrication will
put everything into first-class order. When the loose pulley is, as it
is best for it to be, farthest away from the bearing, held in its place
by the tight pulley and a collar, not only is the tight pulley better
adapted for carrying its load, owing to additional support resultant
from its proximity to the bearing, but such matters of small repair as
come up are much simplified.
[Illustration: FIG. 28.]
Fig. 28 in some degree, aside from the cutting up and heating of the
bearings, illustrates the breaking strain, in addition to the usual
torsional strain, which becomes enhanced in direct proportion with the
increase of breaking strain, to which an out-of-line or out-of-level
shaft is subject. The bends are exaggerated for illustration.
In this instance, the fact of one hanger-bearing being out of line
or level subjects the shaft to a severe breaking strain. The shaft
being both out of line and level does not, if both at the same point,
aggravate matters, as might at first be supposed.
It is true that the full torsional strength of a shaft is only equal
to the weakest portion of it, so that three weak spots more or less
can, theoretically, make no difference one way or the other. But,
practically, there is the undue strain and wear of the bearings at
these points, and if a pulley transmitting any considerable amount of
power is situated anywhere along the length _A B_ it is sure to be
unpleasantly in evidence at all times.
Only an eighth or a quarter out, but oh, what shaft-breaking stories
that fraction could tell!
The following is a simple method for testing the alinement and level of
a line of shafting that is already up.
[Illustration: FIG. 29.]
As in Fig. 29, stretch a line _C_ so that it is exactly opposite the
shafting. Set it equidistant from the shaft end centers _G_ and _F_ and
free from all contact along its entire length except at its retaining
ends _A_ and _B_. Now, it is self-evident, as line _C_ is straight and
set equidistant from the shaft end centers _G_ and _F_, that if you set
the entire center line of the shafting at the same distance from line
_C_, as _G_ and _F_, you are bound to get your shafting into perfect
alinement.
In leveling a line of shafting that is already up, you can, by the use
of a level and perseverance, get it right.
Placing the level at _A_, you are just as likely to raise the first
hanger as to lower the middle one. Look before you jump, even if
compelled to climb to the top of the fence to do so. When you find a
length of shafting out of level, try the two adjacent lengths before
acting, and your action will be the more intelligent for it.
On exceptionally long lines of shafting the following method, in
which the level and a line constitute a check upon and a guide for
each other, can be used to great advantage. Stretch a line so that it
is exactly above, or, if more convenient, below the shafting to be
leveled. With the level find a length of shafting that is level and
adjust your line exactly parallel with this length. Your line now,
free of contact except at its retaining ends, and level owing to its
parallelism to the level shaft length, constitutes a safe _hight level_
guide while the level itself can serve to verify the accuracy of the
finished job.
In lining, whether for level or alinement, unless the shafting line
consists of the same diameter of shafting throughout its entire length,
though of necessity measuring from the shaft circumference to the line,
always base your calculations on the shaft centers. The figures in
Fig. 29 will make this point clear.
The manner of securing the ends of the line under different
circumstances must be left to individual ingenuity. Only be sure that
the line is so placed that the shafting adjustment shall not affect its
original position with reference to the end shaft centers.
Coupling clutches, _i.e._, those joining two lengths of shafting into
one at option, will fail, utterly or partially, if the respective
shafts which bear them are out of line or level with each other. Such a
condition should not be tolerated on account of the danger entailed by
the inability to shut off the power in cases of emergency.
As a general rule, it is most advisable to set a clutch to take as hard
a grip as it can without interfering with its releasing power. Where
a clutch grips weakly, it is subject to undue wear owing to slippage,
whereas a strongly regulated clutch absolutely prevents slippage wear.
III
SHAFTING HINTS[3]
ENGINEERS, machinists and general mechanics are often called upon
to turn their hands to a shafting job. We recognize that all of the
following cannot prove new or even suggestive to most of our readers;
still, some of it for all, and, mayhap, all for some, may not come
amiss.
[3] Contributed to Power by Chas. Herrman.
We all know that to have belting run rightly on pulleys located upon
parallel lines of shafting the shafting must be in absolutely correct
parallel. The slightest deviation, even to a 1-16 inch, often imparts a
marring effect, through poorly running belts, to an otherwise faultless
job.
[Illustration: FIG. 30.]
Fig. 30 shows how to line a countershaft as regards parallelism with
the driving shaft when the countershaft's end-centers are availably
situated for thus measuring. _A_ is the countershaft, _B_ the main
shaft, _C_ is a stick of proper length about 1-1/2 inches in thickness
and width, _D_ a heavy nail--about 20-penny will do--driven into _C_
far enough from its end _E_ to allow of _C_'s resting squarely upon the
top of the shaft _B_.
Rest the measuring rod upon the main shaft, keeping the nail in touch
with the shaft, so that when the _F_ end is in contact with the end of
the countershaft the stick shall be at right angles to the main shaft,
and then mark the exact location _a_ of the countershaft's end-center
on the stick. Do the same at the other end of the countershaft. If
both marks come at the same spot, your counter is parallel; if not,
space between these two marks will show you how much and which way the
counter is out.
It may only be necessary to shift one end in or out a little; and then,
again, it may be that to get into line you will have to throw one end
all the way in one direction and the other all or some in the opposite
direction. But, whichever it be, do not rest content until you have
verified the correctness of your adjustment by a re-measurement.
The nail should be well driven into _C_, so that its position will not
readily change, and it should, preferably, be slant driven (as shown in
Fig. 30), as it thus helps to keep the stick down in contact with the
shaft.
Where an end-center is not available or where there is no clear space
on the main shaft, opposite a center, the method shown in Fig. 31 can
generally be used.
Rest _C_ on top of both shafts and at right angles to the driving shaft
_B_. With _D_ pressed against _B_, place a square on stick _C_, as
shown (stock in full contact with the top of the rod, and the tongue
running down the side of it). Slide along _C_ toward _A_ until the
side of the tongue touches the shaft the other side of _A_. Now mark
a line on the stick down tongue. Do the same at the other end of
your countershaft and the two resultant marks will be your parallel
adjustment guides.
[Illustration: FIG. 31.]
It often happens that a counter, or even line shaft, is end driven from
the extreme end of the main or jack driving shaft with its other end
running beyond the reach of the driving shaft, as shown in Fig. 32.
[Illustration: FIG. 32.]
It is evident that neither method 1 nor 2 can here be applied to solve
the alinement problem. If the driving pulley _B_ and the driven pulley
_A_ are both in place, the following method can be used to advantage.
Fasten, or let somebody hold, one end of a line against pulley _B_'s
rim at _B_^1; carry the line over to _A_ at _A_^2; now sweep the loose
_A_^2 end of the line toward pulley _A_ until the line just touches
pulley _B_'s rim at _B_^2. When the line so touches--and it must just
barely touch or the measurement is worthless--_A_^1 and _A_^2 of pulley
_A_ must be just touched by or (if _B_ and _A_ are not of a like face
width, as in Fig. 32) equidistant from the line.
A single, two-hanger-supported length of shafting thus lined is bound
to be in parallel; but where the so adjusted shaft line consists of two
or more coupling-joined lengths supported by more than two hangers,
only pulley _A_'s supporting portion of the shaft between its immediate
supporting hangers 1 and 2 is sure to be lined; the rest may be more or
less out.
To make a perfect job, fix a string in parallel with shaft length 1 and
2, stretching along the entire length of the adjusted shaft, and aline
the rest of the shaft length to it.
When there are no pulleys in place to go by, or when, as occasionally
happens, the wabbly motion of pulley _B_ (when running) indicates that,
having been inaccurately bored or bushed, or being located on a sprung
shaft length, its rim line is not at right angles to the shaft line,
the method shown in Fig. 33 can be resorted to.
Instead of the nail used in methods 1 and 2, use a board about 8 to
12 inches long and of a width equal to considerably more than half of
shaft _B_'s diameter. By nailing this board _x_ to the measuring rod
_c_ at any suitable angle, you will be enabled to reach from the end
_a_ well into the shaft _B_, as at _b_, and from _b′_ well into _A_, as
_a′_. By keeping the board _x_ along its entire length in full contact
with the shaft _B_ at both 1 and 2, the angular position of rod _C_ is
bound to be the same in both instances, and you will thus (by the use
of a square, as in Fig. 31) be enabled to aline _A_ parallel with _B_.
[Illustration: FIG. 33.]
In all instances of parallel adjustment here cited it is assumed that
both the alined and the alined-to shafts have been, as to secure
accuracy of result they must be, properly leveled before starting to
aline.
The above methods apply to cases where the shafting is already in
place. Where, however, shafting is being newly installed before the
work can be proceeded with, it is necessary, after determining on the
location for the shafting, to get a line on the ceiling in parallel
with the driving shaft to which to work to. Mark that point _A_ which
you intend to be the center line for the proposed shafting upon the
ceiling (Fig. 34).
Rest your measuring rod upon the driving shaft and at right angles to
it, with the nail against it. Hold your square with the stock below and
the tongue against the side of the measuring stick, so that its tongue
extremity touches the ceiling mark _A_, and then mark a line on the rod
along the tongue side _A_. Move your rod along the driving shaft to the
point where the other end of the proposed shafting line is to be, and,
squaring your stick to the driving shaft with the tongue side _A_ on
the marked line of the stick, mark your section point on the ceiling.
Draw a line or stretch a string between these points, and you have a
true parallel to work to.
[Illustration: FIG. 34.]
Owing to the supporting timber _B_'s interference, a square had to
be used; but where the ceiling is clear the rod can be cut to proper
length or the nail be so located as to allow of using the stick
extremity _C_ for a marking point.
When a pulley is handily situated on the driving shaft, the method
shown in Fig. 35 can be used to advantage.
Let somebody hold one end of a line at 1, and when you have got its
other end so located on the ceiling that the line just touches the
pulley rim at 2, mark that ceiling point (we will call it 3). In the
same way get your marks 4 and 5, each farther back than the other and,
for the better assurance of accuracy, as to just touching at 2, remove
and readjust the line separately each time. If now a straight line from
3 to 5 cuts 4, your line 3, 4, 5 is at right angles to the driving
shaft and a line at right angles to this will be parallel to the shaft.
[Illustration: FIG. 35.]
The plumb-bob method is so familiar and, where not familiar, so easily
thought out in its various applications, that we deem it useless to
touch upon it.
The stringers or supporting timbers of drop hangers should be equal in
thickness to about one-fifth of the hanger drop.
Where the stringers run with the hangers and crosswise of the shaft,
both feet of a hanger base are bolted to the same stringer, and this
should be from 1-1/4 to 1-1/2 times the width of the widest portion of
the hanger base. As the hanger is securely bolted to its stringer, this
extra width is in effect an enlargement of the hanger base, and thus
enables it the better to assist the shaft's end motion.
Where the stringers run with the shaft and crosswise of the hangers,
the two feet of the hanger base are each fastened to a separate timber,
and these should be equal in width to the length of one hanger foot,
plus twice the amount of adjustment (if there be any) the hanger's
supporting bolt slots will allow it. In reckoning hanger adjustment, be
sure to figure in the bolt's diameter and to bear in mind that to get
the utmost adjustment for the countershaft the bolts should originally
be centered in the slot; thus a 13/16 × 1-1/2-inch slot, as it calls
for a 3/4-inch bolt, leaves a 3/4-inch play, and this play, with the
bolt in the center of the slot, allows of 3/8-inch adjustment either
way. Without this extra width addition any lateral adjustment of the
hanger would result in leaving a part of the hanger's feet without
stringer support. Such jobs look poorly, and often run still more
poorly. Fig. 36, in its two views, will make the above points clear.
[Illustration: FIG. 36.]
In the stringing of countershafts whose hangers have no adjustment it
often happens, despite all care in the laying out, that they come 1/8
to 1/4 inch out of parallel. A very common and likewise very dangerous
practice at such times is to substitute a smaller diameter supporting
bolt instead of the larger size for which the hanger foot is cored or
drilled, and to make use of the play so gained for adjustment.
That shafting so carried does not come down oftener than it does is due
solely to the foresight of the hanger manufacturers. They, in figuring
the supporting bolt's diameter as against the strain and load to be
sustained, are careful to provide an ample safety margin for overload,
thus enabling the bolt substituted to just barely come within the
safety limit under easy working conditions.
The largest-sized bolt that a hanger will easily admit should
invariably be used, and for alinement purposes either of the following
slower but safer methods should be used.
Rebore the hanger-supporting bolt holes in the stringers to a larger
size, and use the play so gained for adjustment. It is not advisable,
however, to rebore these holes any larger than to one and three-quarter
times the diameter of the bolt to be used; and the diameter of the
washers to be used on top of the stringers should be diametrically
equal to at least twice the size of the rebored holes. That the washers
used, under such conditions, must be of a good proportionate thickness
goes without saying.
When the reboring method cannot be used--as when the hangers are
carried by lag screws, lag-bolts, bolts screwed directly into
supporting iron girders, etc.--it is evident that hanger adjustment
can be secured by packing down one foot of the hanger base, as shown in
Fig. 37.
[Illustration: FIG. 37.]