G. P. (George Payn) Quackenbos.

A natural philosphy: embracing the most recent discoveries in the various branches of physics .. online

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Wheelwork.

268. The wheel enters more largely into machinery than
any other of the Mechanical Powers.

269. Several wheels combined in one machine are called
a Train.

270. In a train of two wheels, the one that imparts the
motion is called the Driver ; the one that receives it, the
Follower.

271. MODES OF CONNECTION. There are three ways in
which motion may be transmitted from one wheel to an-
other: 1. By the friction of their circumferences. 2. By
a band. 3. By teeth on their outer rim.

272. Friction of the Circumferences. One wheel may
move another by rubbing on its circumference, or outer
rim. The wheels are so placed that their rims touch, and
one of them is set in motion. The circumference of each



267. Of what are all machines combinations? What are the chief objects in com-
bining them? 268. Which of the mechanical powers enters most largely into ma-
chinery? 269. What is meant by a Train of wheels? 270. In a train of two wheels,
which is the Driver? Which, the Follower? 271. In how many ways may motion,
be transmitted from one wheel to another? Mention them. 272. How may on o
wheel be made to move another by rubbing on its circumference ? What is the ad-



WIIEELWOEK.



121



Fig. 126.



having been previously roughened, friction prevents the
moving wheel from slipping over the one at rest, and mo-
tion is imparted to the latter. Wheels thus connected
work regularly and with little noise, but will not answer
when a great resistance is to be overcome, and hence are
not much used.

273. Bands. One wheel may be made to move an-
other by means of a band passed round both circumfer-
ences. Such a band is known as a Wrapping Connector.
It is also called an Endless Band, because, its ends being
joined, we never seem to reach them, though the motion is
continuous in the same direction. The band must be
stretched so tight that its friction on the wheels may be
greater than the resistance to be overcome.

Fig. 126 shows how wheels are connected by an
endless band. If the follower is to turn in the same
direction as the driver, the band is passed over it
without crossing, as in A ; if in the opposite direction,
the baud is crossed, as in B.

274. The bands used for this purpose are generally
made of leather, or gutta percha [pert'-sha]. The
wheels may be far apart, if necessary ; and on this
account, as well as because a great amount of power
may thus be transmitted, the wrapping connector is
much used. The motion imparted is exceedingly reg-
ular, any little inequalities being corrected by the
stretching of the band.

275. Fig. 127 shows the different forms given to
the circumferences of wheels, in order that the band
may not slip off. A's circumference is concave, or
hollows towards the centre, with a rim on each side.
B's is the same, with a row of pins down the centre.
C's circumference is even across, with a rim on each
side. D has no rim, but bulges out in the centre, so
that when the band tends to approach one side it is
pulled back by the tightening on the other.

vantage, and what the disadvantage, of this mode of connection ? 273. What is a
Wrapping Connector? What other name is given to it, and why ? How tight must
the band bo? In passing from the driver to the follower, when is the band crossed,
and when not ? 274. Of what are endless bands usually made ? By what advantages
is their use attended ? What renders the motion imparted by wrapping connecto:s
exceedingly regular ? 275. Describe the different forms given to the circumferences
of wheels on which a wrapping connector is to act. 276. What is the third way in

6




Fig. 127.




122



MECHANICS.




Fig. 128. 276. Teeth. One wheel may be made to

move another by means of teeth on the circum-
ference of each. A toothed wheel is shown in
Fig. 128.

277. Small toothed wheels combined with
large ones are called Pinions, and their teeth Leaves.

278. Two or more wheels connected by teeth are called
Gearing. When so arranged that the teeth work in each
other, they are said to be in gear; and when not, out of
gear.

Fig. 129. Figure 129 shows a

train of wheels and pin-
ions in gear. To find
how great a weight will
be balanced by a given
power with such a
train, multiply the pow-
er successively by the
number of teeth on the
wheels, and divide by
the product of the num-
ber of teeth on the pin-

TP.AIN OF WHEELS AND PINIONS. io ns. For instance, in

Fig. 129, let the first large wheel have 18 teeth, the second 18, the third 27,
and the fourth 27 ; and let each pinion have 9 teeth. Then (leaving friction
out of account) a power of 2 pounds will balance a weight of 72 pounds. For




1SX21X27 = 472392
9X9X9X9 = G561
472392 divided by 6561 = 72

279. KINDS OF TOOTHED WHEELS. There are three
kinds of toothed wheels ; viz., Spur-wheels, Crown-wheels,
and Bevel-wheels.

280. Spur-wheels. Spur-wheels have their teeth per-
pendicular to their axes, as shown in Fig. 120.

The teeth are either made in one piece with the rim, or



which one wheel may be made to move another ? 277. What are Pinions ? What
are the teeth of pinions called ? 278. What is Gearing ? When are wheels said to he
in gear? When are they said to be out of gear? What does Fig. 129 represent?
With such a train, how do you find how great a weight will be balanced by a given
power? Give an example. 279. How many kinds of toothed wheels are there?
Name them. 280. Describe Spur-wheels. How are the teeth -made ? What are



WHEELWOBK.



123



consist of separate pieces set into the rim. In the latter
case, they are called Cogs.

In mills, Cog-wheels are gen-
erally used with Trundles, or Lan-
terns, as represented in Fig. 130.

A is a large cog-wheel. B is a trundle,
consisting of two parallel discs and an inter-
vening space traversed by round pins called
Staves, so arranged as to receive the cogs of
the other wheel.

Mill-wheels are generally made -of cast-
iron ; but they are found to work most smooth-
ly when one of them has wooden instead of
iron teeth. Wooden teeth are therefore often
set in the larger one, which is then called a
Mortice-wheel. COG-WHEEL AND TEUNDLE.

281. Crown-iD heels. Crown-wheels have their teeth
parallel to their axes.

Fig. 131.

Fig. 132.






CROWN-WHEEL AND PINION.



HAND-MILL.



Fig. 131 represents the contrate-wheel and pinion of a watch. B, whose
teeth run the same way as its axis, is a crown-wheel. A, whose teeth are at
right angles to its axis, is a spur-wheel.

Fig. 132 shows how a crown-wheel worked by a winch is combined with
a trundle in a hand-mill used in Germany and Northern Europe. The crown-
wheel moves vertically, but it communicates a horizontal motion to the trun-
dle, which in turn imparts it to the mill-stone.

282. Bevel-wheels. Bevel-wheels are wheels whose teeth



Cogs? In mills, with what are cog-wheels generally used? Describe a Trundle
Of what are mill-wheels generally made ? What is said of their Teeth ? What is a
Mortice-wheel ? 2S1. Describe Crown-wheels. What does Fig. 131 represent ? De-
scribe the hand-mill represented in Fig. 132. 282. What are Bevel-wheels? What



124



MECHANICS.



form any other angle with
their axes than a right angle.

A pair of bevel-wheels
in gear are shown in Fig.
133.

283. RACK AND PIN-
ION. Circular motion is
converted into rectilinear
(that is, motion in a straight
line) by means of the rack BEVEL-WHEELS.
and pinion, represented in Fig. 134. As
the pinion A revolves, its teeth work in
Fig. 134. those of the rack

B C, moving it for-



Fig. 133.





BACK A.MJ IM.MU.N.



ward in a straight line.

284. FORGE-HAMMER. A toothed
wheel may produce an alternate up-and-
down motion, as in the case of the Forge-
hammer, represented in Fig. 135.

The wheel is so placed that its teeth successively
come in contact with the handle of the hammer, which
turns on a pivot. As the wheel revolves, a long
tooth carries the lower end of the handle down and
raises its head. As soon as the tooth releases the handle, Mie head of the
hammer falls on the anvil by its own weight. A new tooth then comes into
play, and the operation is repeated.

285. CRANKS. The Crank is much used in machinery
for converting circular motion into rectilinear, or rectilinear




THE FOBGE-IIAMilEK.



Fig. 136.



into circular. It has different forms, but is
generally made by bending the axle in the
way represented in Fig. 136. As the wheel
to which it is attached turns, the crank A
also revolves, and causes the rod B, with
which it is connected, to move alternately
up and clown.

does Fig. 133 represent ? 2S3. How may circular motion be converted into rectilin-
ear? Describe the working of the Rack and Pinion. 2S4. What kind of motion does
a toothed wheel produce in the case of the forge-hammer ? Explain the \vo. king of
the forge-hammer. 2S5. For what is the Crank used ? Describe its usual form, and



THE CUAKK.




THE CRANK. * 125

The point at which the rod stands at right angles to the
axle (as in the Figure) is called the Dead-point. Two dead-
points occur in each revolution. When at either, the crank
loses its power for the instant ; but the impetus carries it
along, and as soon as the dead-point is passed it again be-
gins to act.

286. Another form of the crank is exhib- Fig. 137.

ited in Fig. 137, which shows how a wheel is
moved by a treadle-board worked by the foot.
A is the treadle ; B C is a cord passed round
the pulley D, and attached to the crank E,
which is connected with the axle of the wheel
F. When the foot bears the treadle-board
down, the end of the crank is raised to its
highest point. Here it would remain if the

, , AT. i_ j i_ j. j.i / j. CKANK AND TEEADLE.

loot were kept on the board ; but, the loot

being removed, the impetus of the wheel carries the crank round again to its
lowest point, raising in turn the end of the treadle-board. The foot is now
applied again with the same effect as before, and continuous motion is thus
imparted to the wheel.

287. FLY-WHEELS. The motion of machinery must be
even and regular. Both power and resistance must there-
fore act uniformly ; if either increases too rapidly, the sud-
den strain is apt to break some part of the works. To
prevent this, the fly-wheel is used.

The fly-wheel appears in various forms, but generally
consists of a heavy iron hoop with bars meeting in the cen-
tre. It is set in motion by the machinery, and by reason
of its weight acquires so great a momentum that irregu-
larities either in power or resistance, unless long continued,
have but little effect. If, for instance, the power ceases to
act for a moment, or the resistance suddenly increases or
diminishes, the great, momentum of the fly prevents the
motion of the machinery from varying to any great extent.
2S8. The fly-wheel also accumulates power, and thus enables a machine
to overcome a greater resistance than it could otherwise do. The power,

explain its operation. What is meant by the Dead-point of the crank ? What is said
of the crank at its dead-point ? 280. What does Fig. 137 represent ? Explain the op-
eration of the crank and treadle. 287. For what is the Fly-\vhccl used ? Of what
does it generally consist? Explain how the fly-wheel prevents irregularities of mo-
tion. 288. For what other purpose is the fly- wheel used? How does the fly-wheel



126 MECHANICS.

allowed to act on the fly alone for a short time, gives it an immense momen-
tum ; and this momentum directly aids the power, when the machine is ap-
plied to the required work.

Clock and Watcb Work.

289. One of the commonest and most ingenious appli-
cations of wheelwork is exhibited in clocks and watches.

290. HISTORY. The advantages of combining wheels
and pinions were partially known as far back as the time
of Archimedes ; yet they were comparatively little used in
machinery, and not at all for the measurement of time.

Instead of clocks and watches, consisting of trains of wheels, the ancients
used the sun-dial, and clep'-sy-dra or water-clock. The former indicated the
hour by the position of the shadow cast by a style, or pin, on a metallic plate;
the latter, by the flow of water from a vessel with a small hole in the bottom.
The dial was of course useless at night ; and neither it nor the clepsydra,
however carefully regulated, could measure time with any great degree of
accuracy.

Even Alfred the Great, 9S5 years after Christ, had no suitable instrument
for measuring time. To tell the passing hours, he used wax candles twelve
inches long and of uniform thickness, six of which lasted about a day. Marks
on the surface at equal intervals denoted hours and their subdivisions, each
inch of candle that burned showing that about twenty minutes had passed.
To prevent currents of air from making his candles burn irregularly, he en-
closed them in cases of thin, transparent horn, and hence the origin of the
lantern.

291. Clocks moved by weights were known to the Sar-
acens as early as the eleventh century. The first made in
England (about 1288 A. D.) was considered so great a work
that a high dignitary was appointed to take care of it, and
paid for so doing from the public treasury. The usefulness
of clocks was greatly increased by the application of the
pendulum, which was made about the middle of the seven-
teenth century.

"Watches seem to have been first made in the six-
aid the power? 289. In what do we find one of the most ingenious applications of
wheel-work ? 290. What is said of the knowledge of wheel-work possessed by the
ancients? What did the ancients use for the measurement of time? How did tho
sun-dial indicate the hour ? [low, the clepsydra ? What is said of the accuracy of
these instruments ? How did Alfred the Great measure time ? What was the origin
of the lantern? 291. When were clocks moved by weights first made by the Sara-
cens ? "When was the first made in England ? How was this clock regarded ? What



CLOCK AND WATCH WORK. 127

teenth century, though it is not known who was their in-
ventor. For a time they were quite imperfect, requiring to
be wound twice a day, and having neither second tfor min-
ute hand. The addition of the hair-spring to the balance,
by Dr. Hooke, in 1658, was the first great improvement.
Others have since been devised ; and chronometers (as the
best watches, manufactured for astronomers and naviga-
tors, are called) are now made so perfect as not to deviate
a minute in six months, even when exposed to great varia-
tions of temperature. *'

292. CLOCK-WORK. In clocks, except- siitjyis are moved
by springs similarly to watches, the moviiqBrawer is a
weight ; to which, when wound up, gravity givSp constant
downward tendency. In its effort to descend, it sets in
motion a train of wheels and pinions ; and they move the
hands which indicate the hours and minutes onthe face.

The motion of the wheels, though caused by
the weight, is regulated by the pendulum and art
apparatus called the Escapement, shown in Fig.
133. The crutch ABC moves with the pendu-
lum. As the latter vibrates, the pallets B, C, are
alternately raised far enough to let one tooth of
the scape-wheel pass, its motion at other times
being checked by the entrance of one of the
pallets between the teeth. Hence, though the
weight is wound up, the clock does not go till
the pendulum is set in motion. If the pendu-
lum and escapement are removed, the weight
runs down unchecked, turning the various wheels TnE ESCAPEMENT.

with great rapidity. The motion of the wheels is thus made uniform by the
pendulum ; and by shortening or lengthening it we can make the clock go
foster or slower.

2&3. WATCH-WORK. In a watch, there is no room for
a weight or pendulum ; hence a spring, called the main-

preatly increased the usefulness of clocks ? When were watches first made ? What
was the character of those first constructed ? What was the first great improve-
ment ? What is said of the chronometers made at the present day ? 292. What is the
moving power in clocks? How does the weight set the clock in motion? How is
the motion of the wheels regulated? Explain, with Fig. 138, how the Escapement
regulates 'the motion. If the pendulum and escapement are removed, what is the
consequence ? How is the clock made to go faster or slower ? 293. In a watch, what




128 MECHANICS.

spring, is substituted for the former as a moving power,
while the balance and hair-spring take the place of the lat-
ter as a regulator.

The main-spring is either fixed to an axle capable of revolving, as shown

at P in Fig. 140, or is contained within a hollow barrel, connected by a chain

with a conical axle, called the fusee, represented in Fig. 139. A is the barrel,

Fig. 139. within which and out of sight is the

j . ...... |,| ... t main-spring, having one end attached to

the inner surface of the barrel, and the
other fastened to a fixed axle passing
through the barrel. B is the fusee.
TUE FUSKB. ^ le watcu is wound up with a key,

applied to the square projecting from

the fusee. By turning the square the chain is drawn off from the barrel and
wound round the fusee. The barrel is thus turned till the spring in the in-
side is tightly coiled. This spring, by reason of its elasticity, tends to un-
coil, and in so doing moves the barrel round, drawing off the chain from the
fusee, and winding it again around the barrel. The fusee is thus turned, and
carries with it the first wheel of the train, which imparts motion to all the
rest. When the spring has uncoiled itself, the chain, being entirely wound
round the barrel, ceases to move the fusee, and all the wheels come to rest.
The watch is then said to run down.

The reason of the peculiar shape of the fusee is this. The power of the
spring is proportioned to the tightness with which it is coiled, and hence is
greatest when the watch is first wound. The chain is consequently then
made to act on the smallest part of the fusee ; becaus,the nearer to the axis
the force is applied, the less its power of producing motion. As the spring
gradually uncoils, its power is weakened and it is made to act on a larger
part of the fusee. By thus adjusting the size of the fusee to the varying
power of the spring, a uniform effect is secured.

294. An escapement similar to that used in clocks connects the moving
power with the balance. To the latter, also, a very fine spiral spring is at-
tached, which is fastened at its other end to a fixed support. The watch is
regulated by shortening or lengthening this spring, the balance being made
to vibrate faster or slower accordingly.

295. The works of an ordinary watch are shown in Fig.
140. For convenience of inspection, they are arranged in
a line, and the distance between the two plates, and also
between the upper plate and the face, is increased.

takes the place of the weight, and what of the penrlnlum ? What two ways are there
of fixing the main-spring? Explain Fig. 139. How is the watch wound up ? Ex-
plain the working of the fusee. When does the watch run down, and why does motion
then cease? What is the reason of the peculiar shape of the fusee ? 294. What con-
nects the moving power with the balance ? What is attached to the balance ? How



WATCH-WORK.



129



Fig. 140.




WOKKS OF A WATCH.



P is the main-spring, attached
to its axle, without a fusee. The un-
coiling of the spring carries the axle
round, and with it the great wheel N.
N works in the pinion a, and by turn-
ing it turns also the centre-wheel M on
the sume axis, so called from being in
the centre of the
watch. M turns
the pinion b and
the third wheel
L, which in turn
works in the pin-
ion c and causes
the second or con-
trate-wheel R, on
the same axis,

to revolve. R works in the pinion d and carries round the balance or crown
wheel C, which is on the same axis with it.

The saw-like teeth of the balance-wheel are checked (as in the case of the
escapement of a clock) by the pallets p,p, which are projecting pins on the
verge of the balance A. The hair-spring, fastened at one end to a fixed sup-
port, and at the other to the balance, may be shortened by the curb or reg-
ulator, if the watch goes too slow, or lengthened if it goes too fast, thus con-
trolling the motion of the balance and consequently that of the other wheels.
296. The force of the main-spring is so adjusted as to make the great
wheel N revolve once in four hours. The spring generally turns it seven or
eight times round before it is uncoiled, so that with one winding the watch
runs twenty-eight or thirty -two hours. The great wheel N has forty-eight
teeth, the pinion a but twelve ; so that a and the centre-wheel M revolve once
every hour, and their axle, carried through to the face, bears the minute-
hand.

Between the face and the upper plate is a train of pinions and wheels con-
nected with the axle of the centre-wheel. They are so adjusted that the wheel
V revolves once in twelve hours. V carries the hour-hand. It is attached
to a hollow axle, through which the axle of the centre-wheel passes to carry
the minute-hand.

297. Thus we see that the works of a watch are nothing
more than an ingenious combination of wheels, moved by a
spring and regulated by a balance. The arrangement of the

Is the watch regulated? 295. What does Fig. 140 represent ? With the aid of Fig.
140, describe the works of a watch and their mode of operation. How is the watch
regulated? 29G. How great a force ia generally given to the main-spring? How
long does the watch run with one winding ? Explain the arrangement of the minute-
hand. Explain that of the hour-hand. 297. Of what, as we have seen, do the works

6*



130 HYDROSTATICS.

wheels and pinions is such, that there is a constant increase
of velocity and a corresponding loss of power. The great
wheel, which begins the train, revolves once in four hours ;
the balance, which closes it, revolves in one-fifth of a sec-
ond ; but the force of the spring becomes so attenuated
by the time it reaches the balance, that the slightest addi-
tional resistance there, a particle of dust or even a thicken-
ing of the oil used to prevent friction, deranges, and may
stop, the action of the whole.



CHAPTER X.
MECHANICS (CONTINUED).

HYDROSTATICS.

298. HYDROSTATICS and Hydraulics are branches of Me-
chanics that treat of liquids.

Hydrostatics is the science that treats of liquids at rest.
Hydraulics is the science that treats of liquids in mo-
tion, and the machines in which they are applied.

299. The principles of Hydrostatics and Hydraulics are
equally true of all liquids ; but it is in water, which is the
commonest liquid, that we most frequently see them ex-
hibited.

Water abounds on the earth's surface. It covers more than two-thirds of
the globe, and constitutes three-fourths of the substance of plants and ani*
mals.

300. NATURE OF LIQUIDS. Liquids differ from solids in
having but little cohesion.

of a watch consist? What is said of the arrangement of the wheels and pinions?
What is the comparative velocity of the great wheel and the balance ? What is said
of tho force of the spring by the time it reaches the balance ?

298. What sciences treat of liquids ? What is Hydrostatics ? What is Hydraulics ?
299. What is said of the principles of hydrostatics and hydraulics? How much of
the globe is covered with water ? How much of the substance of plants and animals
tonsists of water ? 300. In what respect do liquids differ from solids? What showa



NATURE OF LIQUIDS. 131

Cohesion is not entirely wanting in liquids, as is proved by their parti-
cles' forming in drops ; but it is so weak as to be easily overcome. Thick
and sticky liquids, like oil and molasses, have a greater degree of cohesion
than thin ones, like water and alcohol.

301. Liquids were long thought to be incompressible,
but experiment has proved the reverse. Submitted -to a
pressure of 15,000 pounds to the square inch, a liquid loses
one-twenty-fourth of its bulk. Were the ocean at any point
a hundred miles deep, the pressure of the water above on
that at the bottom would reduce it to less than half its
proper volume.

002. To distinguish them from the gases, liquids are
often called non-elastic fluids ; yet they are not devoid of
elasticity.

To prove this, after compressing a body of water, remove the pressure,
and it will resume its former bulk. Again, if a knife-blade be brought in
contact with a drop of water hanging from a surface, the drop may be elon-
gated by slowly drawing away the blade ; but it immediately returns to its
original shape, if the blade is entirely removed without detaching the drop



Online LibraryG. P. (George Payn) QuackenbosA natural philosphy: embracing the most recent discoveries in the various branches of physics .. → online text (page 12 of 42)