507 Mechanical Movements - Brown Part 7 docx

The con-necting-rods are so arranged thatwhenone pair of connected links is over the dead point, or at the extremity ofitsstroke, the otherisat rightangles; continuous motion isthus insu

ratchet-wheel from vibratory motionof the

armcarrying a pawl.

226 Thismovementisdesignedtodouble

the speed bygears of equal diameters and

supposedtobe impossible. Six bevel-gears

areemployed Thegearon the shaft, B,is

ingear with two others one on the shaft,

F,and the other on the same hollowshaft

with C,whichturns looselyon F Thegear,

D, is carried bythe frame, A, which, being

fast on the shaft, F, is made to rotate,and

thereforetakesroundDwith it. E isloose

on theshaft,F,andgears with D. Now,

sup-pose the two gearson the hollowshaft, C,

were removed andDpreventedfromturning

on its axis;onerevolution givento thegear

on B would cause the frame, A,also to

re-ceiveonerevolution,and as this frame

car-ries withitthe gear, D, gearing with E,one

revolutionwouid be imparted to E; butif

the gears on the hollow shaft, C,were

re-placed, Dwouldreceive alsoa revolutionon

itsaxisduringtheone revolutionof B,and

thuswould produce tworevolutions of E

achainandchain

are left between them for the teeth of the

pulley to enter

228 Another kind of chainandpulley.

229 Anothervariety.

230 Circularmotionintoditto. The con-necting-rods are so arranged thatwhenone pair of connected links is over the dead

point, or at the extremity ofitsstroke, the

otherisat rightangles; continuous motion

isthus insured without a fly-wheel.

231 Drag-link motion Circularmotion

is transmittedfromone cranktothe other

232 Intermittent circular motion is im-partedto thetoothedwheel byvibrating the arm, B When the arm, B, is lifted, the

pawl, C,is raisedfrombetween the teethof the wheel, and, traveling backward over the circumference, again dropsbetween two teeth on lowering the arm,and drawswith

itthe wheel

233 Shows two different kinds of stops

a lantern-wheel

2.14 235 236

237

240

oscillating the spindle, S, the crown-wheel

hasan intermittentrotarymotion

axis of thepallets.

235 Theoscillationofthetappet-arm pro-!

239- Anarrangementof stopsfora spur-duces an intermittent rotarymotion of the Sear

-ratchet-wheel Thesmall springatthe

bot-tomof the tappet-arm keeps the tappet in

240 Represents vaneties of stops for a armrises, yet allowsittopass the teethon

the returnmotion

236 A nearly continuouscircular motion

isimpartedto theratchet-wheelonvibrating

the lever,a, towhich are attached the two

pawls, bandc.

237 A reciprocating circular motion of

pro-duce an intermittent circular motionof the

crown-ratchet or rag-wheel

ratchet-wheel

241 Intermittent circular motion is

im-parted to the wheel, A, by the continuous

circular motion of the smaller wheel with

onetooth

242 Abrakeusedincranesand hoisting

machines Bypulling downtheendof the

lever,the endsof the brake-strap aredrawn

towardeach other,and the strap tightened

on

2d3 244 245

247

power from ahorizontal shaft totwovertical

ones by meansof pulleysandaband

244 Adynamometer,or instrumentused

forascertaining the amountof usefuleffect

given out by anymotive-power It isused

as follows: Ais a smoothly-turnedpulley,

securedonashaftas nearaspossibletothe

motive-power Twoblocks ofwoodare

fit-tedto thispulley, orone block ofwoodand

a series of straps fastened to a band or

chain,as in the drawing, instead of a

com-monblock Theblocks or block andstraps

are so arranged that theymaybe made to

bite or press upon the pulleybymean.s of

the screws andnutsonthe top of thelever,

D Toestimatetheamountofpower

trans-mitted throughtheshaft, it js only necessary

to ascertain the amount of friction ofthe

drum,A,whenit isinmotion,andthe

num-berofrevolutions made At the endof the

lever, D,is hungascale,B,in whichweights

are placed. The two stops, C, C', are to

maintain theloveras nearlyas possibleina

horizontal position Now,supposethe shaft

tobein motion, thescrews are to be

tight-ened and weightsaddedin B, until the lever

takesthe position shown in the drawingat

the requirednumberofrevolutions

There-fore the useful effectwould be equaltothe

product of the weights multipliedbythe

ve-locityatwhichthe point of suspension of the

weights would revolve if the leverwere

at-tachedtothe shaft

245 Bayonetjoint. Onturningthe part,

A,it isreleased from the L-shaped slot in

the socket, B,whenitcan bewithdrawn

246 Representsapantographforcopying,

point, C. B is an ivorytracing-point, and

A the pencil. Arranged as shown, if we

trace the lines ofa plan with the point, B, the pencilwillreproduce itdouble the size.

Byshifting the.slide attached to the fixed point, C, and the slide carrying the pencil alongtheir respective arms, the proportion

towhichthe planistraced willbe varied

247 A mode of releasing a sounding-weight When the piece projecting from thebottom of the rodstrikes thebottomof thesea, it is forced upward relatively tothe rod,and withdrawsthe catchfrom underthe weight,whichdropsoff"and allowstherodto

be liftedwithoutit.

248 Unioncoupling. A isa pipe with a small flange abutting against the pipe, C, with a screwed end; B a nutwhich holds themtogether.

249 Ball-and-socket joint, arranged for tubing

250 Anti-friction bearing Instead of a

shaftrevolving in an ordinary bearing it is sometimes supported on the circumference

of wheels Thefrictionis thus reduced to

theleastamount

251 Releasing-hook,used in pile-driving

machines When the weight, W, is suffi-ciently raised, theupper endsof the hooks,

|A, by which it is suspended,arepressed in-ward by the sidesof the slot, B, in the top

of the frame; theweight is thus

suddenly-released, and fallswith accumulating force on

CZl

258

M

259

.

=1 ^

tobe equallymoved to and fro in the slot,i

byaflat belt.

C This is accomplished by moving the

piece, D, with oblique slotted arms,up and 256. Aplainpulleyforaflat belt, down

253 Centrifugal check-hooks,for

prevent-ing accidentsincase of thebreakage of

ma-chinerywhich raises and lowers workmen,

ores,etc., inmines Aisaframe-workfixed

to the side of the shaft of the mine, and

havingfixed studs,D, attached The drum

on which the rope iswoundisprovided with

a flange, B, to which the check-hooks are

attached Ifthedrumacquires a

dangerous-ly rapid motion, thehooksflyout by

centri-fugal force,and one or other orall ofthem

catch hold ofthe studs, D, and arrest the

drum and stop the descent of whatever is

attachedtotherope. The drum ought

be-sides this to have a spring applied to it,

otherwise the jerk arisingfrom the sudden

stoppage ofthe rope might produce worse

effectsthan itsrapid motion

254 A sprocket-wheel to drive or to be

driven achain

257 Aconcave-groovedpulley foraround

band

258 Asmooth-surface V-grooved pulley

foraroundband

259 AV-groovedpulleyhavingitsgroove notched to increase the adhesion of the

band

260 Adifferentialmovement Thescrew,

C,worksinanutsecuredtothe hubof the wheel, E, the nut being free to turn in a bearingin theshorter standard, but

prevent-ed bythe bearingfrom anylateral motion

The screw-shaftis securedinthe wheel, D

The driving-shaft, A, carries two pinions,

F and B Ifthese pinions were of such size as to turn the two wheels, D and E,

with an equalvelocity,the screwwould

re-main at rest; but the said'wheels being

driven at unequalvelocities, the screw

tra-of

261 262 263

L

P

the weight, W, moves vertically with a

reciprocating movement; the down-stroke

being shorter than the up-stroke B is a

revolvingdisk,carrying adrumwhich winds

round itself the cord, D An arm, C, is

jointedtothe diskand totheupperarm, A,

sothatwhen the disk revolves the arm, A,

movesup and down, vibratingonthe point,

G This arm carries with itthepulley, E

Supposewedetach the cord from the drum

andtie ittoafixed point,andthenmovethe

arm, A, up and down, the weight, W, will

move thesame distance,andinaddition the

movementgivento itbythe cord, thatisto

let us attach the cord to the drum and

re-volve the disk, B,and the weightwillmove

verticallywith the reciprocating motion,in

whichthedown-strokewill beshorter than

the up-stroke,becausethedrum is

continu-allytakingupthe cord

262and263. The firstof these figuresis

\

an endview,andthesecondasideview, ofan

'

arrangement ofmechanism forobtaining aI

seriesofchangesofvelocityand direction.|

Disascrew on whichisplacedeccentrically

'

the cone, B,andC isafriction-rollerwhichi

ispressed against the cone by a spring orj

weight Continuousrotary motion,ata

uni-formvelocity,of the screw, D, carryingthe

eccentric cone, gives aseries ofchangesof

velor'ty and direction to the roller, C It

willbe understoodthatduring every

revolu-tion of the cone the roller would press

against a different partof the cone,and that

it would describe thereon a spiral of the

samepitch as the screw, D Theroller,C,

would receive a reciprocating motion, the

than

but one having one tooth more than the

other, both in gear with the same worm Suppose the firstwheel has 100 teeth and thesecond 101,one wheelwill

gain one

re-volution overthe other during the passage

of 100 x 101 teeth of either wheel across the plane ofcenters, orduring10,100 revo-lutionsof theworm

265 Variable motion Ifthe conicaldrum

has a regular circular motion,and the fric-tion-rolleris madetotraverse lengthwise, a

variablerotarymotion of the friction-roller willbeobtained

266 Theshafthastwo screwsofdifferent

pitches cuton it,one screwing into a fixed

bearing, andtheotherinto a bearingfreeto

move to and fro. Rotary motion of the

shaftgivesrectilinear motion to the mova-blebearing, a distance equaltothedifference

ofpitches, ateachrevolution

267 Frictionpulley. Whentherim turns

in the opposite direction to the arrow, it

gives motion to the shaft bymeansof the pivoted eccentric arms; butwhen it turns

in the directionof thearrow, thearmsturn

ontheir pivotsand the shaftisatrest. The

armsare heldtotherim bysprings

268 Circular into reciprocating motion

bymeansof acrankandoscillating rod.

269 Continued rectilinear movement of the frame with mutilated racks gives an

motion the spur-gear

270 272