7/28/2019 Mechanical Models [1930] 047_section1

1/5

S E C T I O N I Nos. 116Pour principles of mech anics. Belt, chain, rope, foot treadle and

miscellaneous dr ives .

7/28/2019 Mechanical Models [1930] 047_section1

2/5

MECHANICAL MODELSA Descript ion of More ThanOne Hundred and S ix ty MovementsP re se n ted in 10 Sections of 16 P an els E ac hSection I

1. Inclined Pl an e. T h e inclined pla ne is one ofthe basic principles of modern machinery. I tschief purpose is to enable a small force to over-com e a large force. T h e ac t of rolling a ba rrelup a plank into a wagon is a simple example ofth e use of th e inclined pla ne . M odifications ofthis principle are the wedge and screw.2* Lev er. T h e lever is an oth er basic principleof m ech anic s. I t cons ists of a rigid b ar restin gupo n a po int called th e fulcrum . T h e po ints arearr an ge d in m odel 1 as in pliers an d sh ears , m odel2 as in a shovel, model 3 as in the wheelbarrow.The wheel and axle, and pulley are modificationsof a lever.3. W e d g e . T h e w e d g e is o n e of t h e o l d e s tmechanisms and comes under the heading of theinclined pla ne . Som e exam ples of wedges are th eax, chisel , nails, pins , ca rp en ter 's p lane an d cu t-ting tools of nearly all kinds.4. Screw. F ro m th e po in t of view of th e m e-chanic, the screw is simply an inclined planew rapp ed aro un d a cylinder. T h e vise and let-ter-press are examples of the screw whose pur-pose is to ob tain increased press ure. A no the rexample, the jackscrew, is used by builders tolift he av y obje cts w ith th e least effort. T h epropellers of boats and airplanes are furtherexamples .

7/28/2019 Mechanical Models [1930] 047_section1

3/5

10 THE NEWARK MUSEUM

5 . Belt Drives. M achines are of two kindsthe driving and the driven. Some driving ma-chines are steam and oil engines, electric motors,and water wheels. Examples of driven machinesare lathes, drills, planes, and saws. Some con-necting link or means of transmission betweenthe two is necessary. A common method is touse be lts, chains or cogwheels. By twisting aflat belt half way the shafts may be driven atright angles if the belt rotates as indicated inthis specific arrangem ent. In order to m ake belttrack, center of upper pulley must be in linewith righ t edge of lower pulley. In m odel 2reversed motion is obtained by giving the roundbe lt a half tu rn ; and m odel 3 shows be lt instraight line drive with pulleys rotating in samedirection.6. Belt Drives. Left han d model shows me-thod of keeping loose belt taut at all times.Other model shows method of transmittingpower by round belt in different planes pro-ducing the same rotation on the two lower ver-tical pulleys as indicated by arrows.7. Chain drives. Th is panel shows early andmodern forms of chain drive, the later type onthe right being the universally used chain. I t iscalled the silent chain and has small rollers atthe contact points, making an almost frictionlessperformance. The speed of the sprocket wheelsis inversely proportional to the number of teeth.Therefore model 1 shows a speed ratio of 1 to 1and model 2 a ratio of 2 to 1.8. Rope drive. Form of pulley used for trans -mitting power by rope drive, having grooves to

7/28/2019 Mechanical Models [1930] 047_section1

4/5

MECHANICAL MODELS 11

prev ent slipping and to make it a positive drive .The two smaller pulleys below are guide pulleys .Such a drive is used for long distance trans-missionexample: obtaining power in varioussections of an oil field.9. Pulley types. Pulleys are of two kinds, fixedand movable. Both are combined for practicalwork. These are all fixed pulleys which consist ofa wheel with grooved rim, called a sheave, freeto rotate on an axle which is supported in afixed block. A flexible rope or cable passes overthe wheels and these types show variations inrim to keep the be lt from slipping off. Thefourth pulley from the left is essentially for around belt or rope, and because pulley 5 kinksthe rope or belt, it is possible to get the greatestpulling power without slipping.10. Treadle drive. Treadle drive derived itsname from the foot method of obtaining power.The force applied to the treadle is transmittedby the pitm an or connecting rod into rotarymotion by crank or disk.Bell crank drive. Th is device makes use ofan elbow shaped lever. I t is a convenience fortransmitting power in different planes as de-sired.11. Slotted connecting rod. Rota ting diskgives motion to rod with pause at both ends ofstroke. Th is is used on brick making machin-ery . The pause allows mold to be loaded andunloaded at each end of stroke.

Tread le drive. Th is treadle drive dispenseswith wrist pin used in N o. 10 and uses a beltand eccentric or off center pulley.

7/28/2019 Mechanical Models [1930] 047_section1

5/5

IS THE NEWARK MUSEUM

12. Straigh t line drive. The straight line mo-tion of A is converted into rotary motion byaction of crank B working in an S shaped slot.This device does away with oscillating motion ofrod as in No. 11 (upper).13. Slotted bell crank drive. Circular motionof pin in disk, which works inside of the straig ht,slotted yoke, produces an irregular, verticalmotion of rod. Dow nward motion of rod isslow but has a quick retu rn . Exam ination ofaction of rotating pin in yoke explains this.14. Slotted yoke drive. Th is is an example ofrotary motion being converted into straight linemotion. So it is opposite to th a t of N o. 12 .15. Off-center-stop drive. This tread le mo-tion has a spring attachment for bringing thecrank A, when action ceases, back to a positionoff center where it will always start when pres-sure is applied to the foot lever.16. M ul t ip le t rave l mo vem ents . M ul t ip letravel movem ents are very useful. The uppermodel has a m echanical advan tage of 2 to 1 andth e lower model of 8 to 1. The latt er is th a tcommonly used in expanding gates, doors, etc.