US2365311A - Copying lathe - Google Patents

Description

Dec. 19, 1944. I E. TOPHAM COPYING LATHE Filed March 15, 1943 6 Sheets-Sheet 1 Dec. 19, 1944.

- 1.. E. TOPHAM COPYING LATHE Filed March 15, 1943 e sheets-sheet 2 Dec. 19, 1944. 1.. E. TOPHAM COPXING LATHE Filed March 13, 1943 6 Sheets-Sheet 5 I N no 3 a Q3 3 Dec. '19, 1944. ETOPHAM v 2,365,311

COPYING LATHE Filed March 13, 1943 6 Sheets-Sheet 5 E j' v ,p'o. W

' Dec. l9,- 1944. TQPHAM 2365,31]

COPYING LATHE Filed March 1a, 1943 s Sheets-Sheet 6 Patented Dec. 19, 1944 COPYING LATHE.

Laurence E. Topharn, Wenham, Mass, assignor to United Shoe Machinery Corporation, Flemington, N. J., a corporation of New Jersey Application March 13, 1943, Serial No. 479,014

4 Claims.

This invention is concerned with copying lathes and more specifically with the motions of a swing frame that emanate from. radial variations of a rotating model. frame type the swing aXis is usually fixed and parallel with the turning axis of the model. Consequently, regardless of whether the model or the model wheel is carried by a swing frame, the relative movements of the model wheel and the turning axis of the model are always in planes at right angles to that axis, except as they are slightly modified by components of relative feeding movement lengthwise of the turning axis.

The right angular relation above mentioned is, of course, ideal only with respect to those portions of the surface of a, model that lie parallel with the turning axis and develop'no wedging effeet, but is tolerable with respect to those portions of the surface that are inclined or pitched with respect t a normal relation, provided the pitch is not so steep as to develop an excessive wedging effect that would cramp the elements or distort .the reproduction. These considerations have been recognized inthe development of the present invention which is embodied in a lathe capable of turning the forepart of a two-part last without leaving any stub at the toe end, or of turning a heel part without leaving a stub.

A novel feature of the invention is embodied in linkages carried respectively by two feed carriages one of which is a model wheel carriage and the other a cuttercarriage. Each linkage includes a swing frame. A model wheel is carried by. one swing frame and a rotary cutter is carried by the other. The model and the block or work piece to be shaped are both arranged to turn on a common axis which is preferably fixed.

One of the novel features of the swing frames is.

that the axes of their fulcra or swing centers are transverse to the turning axis of the model and the'block. Another is that the fulcra of the swing frames are arranged to float, each with respect to its feed carriage, but their changes of location due to floating are constrained to produce desired alterations in the directions of those movements of the model wheel and the cutter that emanate from the shape of the model.

Still another novel feature of theinvention is a supplemental linkage by which the floating fulcra above mentioned are shifted and maintained in coordinated relation as the cutting or 4 turning operation progresses. In the construc tion herein'disclosedthis shifting of the floating fulcra is produced-by the feed or traverse of the model wheel carriage, but its amplitude and timing are both arbitrary.

The features above mentioned are embodied in a lathe in which the model is supported entirely by a face plate at the butt end thereof, and the work block is likewise supported. Consequently,

In prior .lathes of the swing as to copying a forepart model, the toe end thereof will turn in the air and be entirely accessible for engagement by the model wheel, and similarly, the outboard end of the block will turn in the air and be entirely accessible for complete shaping by the cutter. I

The invention also providesnovel girth-grading means embodied in still another linkage connecting the two linkages heretofore mentioned. The grading linkage is responsive only to those components of movement of the model wheel swing frame that afiect the distance between the turning axis and the point of contact where the model wheel engages the model. This linkage communicates corresponding components of motion to the swing frame by which the cutter is carried, and these components may be graded downor up from a 1:1 ratio by adjusting one of the pivotal joints of the linkage toward or from a fixed center of oscillation.

Referring to the drawings,

Fig. 1 is a front elevation partly in section of a copying lathe embodying the invention;

' Fig. 2 is a top plan view thereofminus a por tion broken away at the lower left;

i Fig, 3 is a top, plan view of the feed carriages,

and the length grading mechanism;

Fig. 4 is a top plan view of a linkage operated by one of the feed carriages for altering the lines of movement of the model wheel and the cutter toward and from the turning axis? Fig. 5 is a top plan view including the turning spindle, a model, a work block, and a linkage by which width grading may be regulated;

Fig. 6 is a. sectional elevation of the transmission means intersected by line VI.VI in Fig. 1;

Fig. '7 is a sectional elevation of the length grading mechanism viewed from the front;

Fig. 8 is a schematicview in which zigzag lines represent the path of travel of the point of contact between the model and the model wheel as the latter traverses the former. 1

Fig. 9 is an elevation of connections related to the clutch-controlling mechanism-shown in Fig. 6; and

Fig. 10 is an elevation of gearing and controls related to the length-grading mechanism shown in Fig. 7.

Some features of the illustrated machine are essentially the same as corresponding features of the copying lathe shown and described in Letters Patent of the United States No. 2,072,228, granted March 2, 1937, on a joint application of Topham and Knott. For this reason, features common to both disclosures are described only brieflyhereinwork block is afiixed to a holder 13 and its out board end turns in the air and afiords unobstructed access to a rotary cutter 21. The holders l2 and I3 are both aflixedito aespindlel4 journaled in fixed bearings I51 'The'spindle also has bearings in a gear case It and is provided with a gear H by which it may bemotated. The

main frame structure 18 by which the-various mechanisms aresupported.

The .modehwheel 20.and1the.c.utter 2L (Fig. .3)

are; carried. respectively byswingirames .22; and.

23., and the-latter are-carriedi.respectively by feed carriages 24: and .25. The. carriageearemovable.

toward and from each other.0n..tracks 26' and 27' (Fig; 2). and thereby constrained. to pathsparah lel with the. turning axis. A. The. swing. frames. are connected to their carriages. by compound, linkages .the pivotal. axesof. which are. all. parallel.

with. each. other but, transverse. to. the turning, axis A.

Oneend'of. the. swing frame 22 iscOnnected to its carriage by alink 28' andlthe. swing frame. 23 is likewise-connected to. its. carriage by a link 29. The pivotal connectioneare. formed by concealed bal1.bearings,.and.f.or thisreason their pivotal centers are indicated by dots 30, 3|; 3'2 and33. The centers 30 and3llare. carriage centers, but the centers 32 and 33"swing.about them and may be regarded as. floatingcenters. Radius Bandradius Crepresentjapproximately the range of angulanmovementofthe. center 32; andradii.

D and .E represent. thatbfi the. center. 33; but. the limits of such movementfare variable according to the model selected andregulation ofithewidthgrading mechanism. hereinafter described.

The swing. .frame 22 is. also. connected to its.

carriageby anarticulatelinkage comprising two links. 34yandz35l. A-pivot 3.6.connects the.link.3.4.

andlthe. swing, frame, .an. individual pivot 31 (dotted) connects thelink 351 andthe. carriage, and the-pivot,pin 38iconnects.the.links to each other. Theforcezof. amounterweight. 2.00 (Figs. 1 and.2) is applied to theswing irame22 by mechanism hereinafter. describedv and the. model wheel. is

thereby held against -the. rear. side. of the. model.

with pressure toward. the front.-

Now, disregarding all. other. motions, as the.

center3i2. floatsinan arccaboutthecenter Bil-the center. .3 B; will. float .in .an.arci. about .the center 33, andso.longasthelatter remains ononnear radius F the resultant lineof. travel-.of. the. model wheel will. be. oblique: to. a. plane at..ri'ght. angles. to. the turning axisA. Themaximumobliquity of; this line is indicated by an arrow in Fig. 8; but as the model. wheel. traverses themodel from. planaH toplaneJ the obliquity is. gradually eliminated,

In Fig. 8 the zigzag line Z represents the pathof the pointof. contact between .the model .wheel. and themodeL -It; is. to. be. observed that the: lines of. travelof: the model. wheel. at. the toe. end of the model areinearlyxif notexactlynormal with respectv toatangentpf. the surface or". themodel. Thisapproximation-hf.normalcy enablesthemode el wheel tmbear againstthe endof the modelwithout developing so much wedging effect as .to spring theselements; away fromtheir. true. relations.

model wheel is obtained by moving the link 35 (Fig. 3) about its pivot 31 to shift the pivot 38 from radius F toradius G. The pivot 38 is the one about which the link.34lswings;as the model wheel moves toward and-from the turning axis A. The links 28 and 34 are so situated that when the center 38 is on radius G the lines of movementof the model wheel will be nearly if not exactly at right angles to the turning axis.

bearings l5 and the gear case are parts of the (ill The. regulation of the lines. of travel of the 75 The. linkage carried by the cutter carriage 25 is similar" to but :the reverse of that above described andhasacorresponding regulating efiect on thelinesotmovement of the cutter 21. The cutter is carried by a driven shaft 40 and this is journaled in bearings in the swing frame 23. The

connectionsbetween .the swing -frame 2.3 and; its carriage include not; only- ,tlie; link. 29', but. also: the. links 4L and;42. The pivoti43lconnects the. link. and the swing fiamaan individualpivot. 44 connectsthe .link .42. and the. carriage, and a. pivot 45? connects thelinks. to. each other. The, pivot 45" corresponds .to the pivot. 38. andmay be shifted in like. manner. aboutit'scarriage pivot. to modify or alter.v the. lines ofmovementoi. the cutter toward andirom the. turning axisA inv accordance. with the. principle developedin Rig. .8.

Fig: 4 illustrates a linkage. by which the links 3'5'and 42 may be adjusted with respect to their carriages to shift their pivotal centers 38 and 45ers above pointed'out. In. reading Fig. 4 it. must be borne in mindthat thecarriages 24 and. 25? move towardeach other when the. lathe isin. operation-and thatflthe linkage about. to be described derives its operatingv efiectffrom the traverve of the carri'age24. Figs. 3'and 4,.both top. views; may be considered'together and' it is to be. understood that the elements in Fig. diaresituatedf at 'a'l'evel below that 'ofthecarriages.

An. operating arm 46. underlies, the. carriage. and is connected to the main frame. structure. It by averticallfulcrum stud 4''. Cam. surfaces" 48 formed in'the arm provide a slot. which. is occupi'ed by a roll 49 under the carriage and carried thereby; As the carriage and the roll travelflfrom left to right they shift the. armAB. from the posi: tionrepresented in full'linestothat represented in broken. lines. This shifting, occurs while the. model wheel traverses, the modellf'rom planeHf to: plane J (Fig: 8). but beyond. that stage. the. roll 49 traverses a portionof the arm that has no. camming effect and merely maintains the armin. one'position to thetenminus of the traverse. The motion of the arm 46.:is impartedto a horizontal. bar 53 carried by parallel links 5! one ofwhich. is.

connected to the arm by an operating link 52.

; the carriages. 24.and 25. The,slots:55. and. 56lare' occupied by rolls 5! and, 58. A. rock. shaft 59 journaled in the carriage 24; (Fig. 1), is. provided with an upper arm. 60. and a lower armil, the r0115! being carriedlby the. latter. In like manner a rock. shaft. 62. journaled inthe carriage 25. is provided with an upper arm-63..and.a1lower arm. 54* by which theroll 5.8.iscarried. Angular.movement of the. arm. 60. is. imparted. tothe link. 35. (Fig. 3.). by. a link.6.5. to.shift-the pivotal center 38, and. corresponding unovementof the arm- 63 are both overned by the design of the cam arm 46 which may be replaced by one of different design for work having different characteristics of shape.

Fig. illustrates girth-grading linkage embodying novel features designed for a lathe of the type I under consideration. This linkage i situated at a level above that of the linkage shown in Fig. 3 and is mounted on a superstructure of the frame I8. Some of the pivotal centers of this linkage are provided by concealed ball bearings and for this reason are indicated by dots. Four fixed centers II, I2, I3 and I4 constitute the fulcra of bell cranks I5, I8, 11 and IS. The bell cranks I5 and I6 carry a bar I9 having a slot 80 while the bell cranks 71 and i8 carry a corresponding bar 8| having a slot 82. The centers 83 and 84 represent pivotal connections for the bar I9 and the centers 85 and 86 represent pivotal connections strains the bar I9 to parallel movement and maintains the slot 89 in parallelism with the paths of the carriages 24 and 25.

In like manner a link 98 pivotally connecting the bell cranks TI and I8 on centers 9| and 92 constrains the bar 8| to parallel movements and maintains the slot 82in parallelism with the paths of the carriages. Although the bars 89 and 8| have components of lengthwise movement as well as components of widthwise movement only the widthwise components are utilized, the lengthwise component being absorbed or nullifled by the slots 88 and 8 I. Moreover, the amplitude of the movements of the bar 8| may be graded up or down with respect to those of the bar I9. For this purpose the bell cranks I6 and l! are connected by an individual link 93 of which cnepivotal connection is on the center 9i and the other provided by a stud 94. This stud is adjustable toward and from the fulcrum or fixed center I2 of the bell crank IE for the purpose of regulating the grade, but when its distance from I2 is exactly equal to the distances I I88, I39I and I492 the ratio of the grade will be 1:1.

The counterweight 288 (Figs. 1 and 2) is connected with the bell crank I8 by a cable 2M that runs over azsheave 282.

To provide for adjusting the stud 94 a slot 95 is formed in the bell crank I6 and the stud ex- 1':

tends through it. Moreover, the slot is arcuate and its radiu of curvature equals the distance 9I--9 I. When the parts are in the positions shown in Fig.5 the slot is concentric with respect to the center 9|. It is to be observed that the angle 8 i-1294, the angle 85-'I3--9I andthe angle 85-'I4--92 are equal, also that the angle B4-I289 and the angle 83-II'--88 ar equal. The location of the center 89 is not changed by adjusting the stud 94 along the slot 95.

Figs. 1 and 2 include a convenient mechanism for adjusting the stud 94. An operating handle I80 in the form of a crank is attached to a shaft 95. Rotation of the shaft is transmitted by a worm 91, a worm wheel 98, and a vertical shaft 99 to a pinion I III This pinion engages teeth on a rack bar I82 the rear end of which is pivotally connected to a yoke I98 by a pivot stud I84 which extends through a slot I05 in the bell crank 16 and is guided thereby. The grading stud 94 has 23 are connected at a pivotal center I I9.

" Wise in a bearing in the carriage 2 3.

hearings in the yoke'I03 and is shifted thereby. The motions of the girth-grading linkage are derived from a point I06 on the swing frame 22 (Fig. 3) at which point a link I0! is pivotally connected to the swing frame. The rear end of this link is carried by an arm I08 (Fig. 5) to which it is pivotally connected by a pin I09. The arm is carried by the carriage 24 to which it is connected by a bracket III! and a pivot pin III. A roll I I 2 carried by the link I81 occupies the slot in the gradin bar 19 and its components of movement toward and from the turning axis A are thus utilized to actuate the grading linkage.

Still referring to Fig. 5, the movements of the grading bar I9 produce corresponding movements of the grading bar 8|, and the effective components of such movements are imparted to the swing frame 23 by a roll H3 and a link II 4 on which the roll is mounted. The rear end of the link H4 is carried by an arm I I5 to which it is pivotally connected by a pin H6. The arm is carried by the carriage 25 to whichit is connected by a bracket I I1 and a pivot pin I I8. The forward end of the link H4 and the swing frame The axis of this center intersects the cutting portion of the cutter 2I, and in like manner the axis of the pivotal center IIJBintersects the corresponding portion of the model wheel 28. The location of the axis last mentioned is indicated by a dot I86 in Fig. 8.

The carriages 24 and 25 are operated by length grading mechanism of the type shown and described in the aforesaid Letters Patent No.

This mechanism is also shown herein in Figs. 2, 3 and 7. As shown in Fig. '7 a worm I28 is provided to drive a worm wheel I2I affixed to a feed shaft I22. The worm i carried by a shaft I 23 capable of being moved manually to raise the worm into engagement with the worm wheel to start the rotation of the shaft I 22. The feed shaft has a right hand feed screw I24for operating the carriage 24 and a left hand feed screw I25 for operating th carriage 25. A nut I26 carried by the carriage 24 cooperates with the riage 25 cooperates with the feed screw I25. When the shaft I22 is driven by the worm I28 it feeds the carriages toward each other, but the feed screw I24 is steeper than the feed screw I25, the difference in steepness being sufficient to grade down 6 /2 sizes when the nut I26 is held against rotation. Nevertheless, the nut I26 may be turnedwith respect to the carriage 24 at a controlled and variable rate to counteract a component of the feeding effect of the screw I24.

A spur gear I28 surrounding the nut I26 and formed thereon is engaged by rack. teeth formed on a bar I29. This bar is arranged to slide end- Its rear end is provided with a shoe I38 that has tongue and groove connection with a track I3I afiixed toa support I32. The latter is connected to the frame I8 by a stationary pivot pin I33 about which it may be adjusted to place the track I 3i in parallelism with the carriage tracks 26 and 2? or at various angles of inclination with respect to the latter. and a gear segment I34 with which a manually operable adjusting worm I35 cooperates. The worm I35'is carried by a shaft I 36 to which rotation may be transmitted from a hand crank I 3! (Figs. 1 and 2) by a train of connections including a shaft I38, a pair of gears (not shown) a shaft I39 and another pair of gears (not shown).

A link 2I5 couples the support I32 connection I 4Il-whioh enables the shoe to partake of the angular adjustments of the track I 3!. When the latter-parallels the carriage tracks the lathe will grade down 6 /2 sizes, but when the track I3I is inclined at its maximum angle the,

lathe will have a 1:1 ratio.

Referring to Fig. 10, rotation i transmitted to the Wormshaft I23 by a driving train comprising a pair of spiral gears MI and I42, a shaft I43 (refer now to Fig. 6), a worm wheel I44, worm I45,shaft I 46, driven clutch member I47, driving clutch member I48, spiral gears I49, shaft I50, earsv II and. I52, pulley I53, and belt I54, The belt is driven by a pulley (not shown) on the shaft of a motor I55 (Fig. 1).

Again referring to Fig. 10, the wormshaft- I23 is iournaled in a bearing member I56 suspended from the shaft I43 and arranged to rock thereon for the purpose of shifting the worm I into and out of engagement with the worm wheel I2I. A tension spring I57 is arranged to effect disengagement, but the member I56 is provided with a spring pressed latch I58 the rear end of which is arranged to be lodged on the upper surface of a block I59 to maintain the worm I26 in its driving position. The member I56 is provided with a handle I60 by which to raise the worm and place the latch above the block I59.

The controlling mechanism last described is upplemented by an automatic knock off (Figs. 1 and 7) designed to release the latch I58 from the block I59 when the cutter carriage reaches the terminus ofits traverse. For this purpose a bracket IBI afiixed to the cutter carriage is provided with a striker I62 arranged to displace the block I59 against the'stress of springs I63 that normally keep the block in itsoperative position. The block is arranged to slide in a horizontal groove in a stationary supporting bracket I64.

A hand wheel I72 (Figs. 1 and 2) is provided to move the carriages 24 and 25 away from each other when the screw shaft I122 is disconnected from its automatic driving means. For this purpose the right hand end of the screw shaft is provided with a bevel gear I73 in constant mesh ith a pinion I74 carried by a shaft I75 to which the hand wheel is afiixed.

Referring again to Figs. 1 and 6, the shaft I 45 also transmits rotation to the model III and the Work block II. The train of connections for this purpose comprises a pair ofbevel gears I65 and I66, spur gears I67 and I68, shaft I69, and spur gears I70, I71 and I7. The'three gears last specified are enclosed in the gear case. I6.

Fig. 6 includes starting and stopping mechanism capable of being operated manually to start the shaft I46 and of being operated both manually and automatically to stop the shaft. This mechanism is to all intents and purposes the same as the corresponding mechanism shown and described in the aforesaid Letters Patent No. 2,072,228, although the handles for controlling it are arranged diiferently.

The driving clutch member I49 is loose with respect to the shaft I46 and is movable to and from engagement with the driven clutch member I47. A bell crank I76 for shifting the member His is arranged to rockon a fulcrum pin I77 and is provided with a pin I7.8 by which it may be operated. This pin extends through a slot in a rocker I79 and is additionally connected to the rocker by a tension spring I80 that causes therocker to shift the member I48 into and out of engagement. The'rocker is carried by a lever The :rackbar. I29 andtheshoe I30 have-a pivotal; I8I: loosely mounted'ona bearing portion formedi on. the left-hand end of the shaft I22. Aglinlc I82 connects the rocker and an arm I 83 affixed".

to a controlling shaft I84. This shaft extends:

to the right-hand end of the lathe (Fig. 2) where itisprovidecl with a bell crank I85 (Fig..9):., .A.

spring I86 normally rocks the shaft I84 in a. counterclockwise direction but manual controls.

also connected to the bell crank I85 provide for rocking the shaft clockwise. A link I 87 anda lever I88 (Fig. 2) connect the bell crank and the rear end of a manually engageable bar 189; The lever I88 is mounted on a fulcrum stud I90- When the bar I89 is pulled forward a hook. I9I. on one edge thereof may be caught and held bya latching stud I 92. The'operator will make thisengagement when he wants automaticstoppage of the work spindle I4 at a predetermined).

position in its cycle of revolution. This: will? place the arm I83 in the positionshown in-Flg; 6; the clutch then being engaged to drive the shaft"; I45. A worm I93 on this shaft drives a worm wheel I94 by which a cam I95 is carried, and when the high part of the cam rocks the lever- I3I the latter swings the rocker I'I9 downward far enough to put the spring I 88 in a position to retract the clutch member I48. To restart the shaft I45 while the high part of the cam I95 is against the lever IBI as shown in Fig. 6; the operator hasonly todisengage the bar I89 (Fig. 2) from the stud I92 and let go. Then the spring I85 will depress the arm I83 (Fig. 6) and thereby rock the rocker I7!) clockwise. This will shift" the member i48 to the member I47.

To retract the model wheel and the cutter from the turning axis the operator will pull forward a hand lever I55 (Fig, 2) supported by a longitudinally movable bar I9? and connected thereto by a pivot stud I93. The left-hand end of the lever is arranged to bear against a fixed fulcrum pin I99. As the. bar I537 is pulled forward a lug 254 carried thereby will engage an arm 203 formed on the bell crank 77, and thereby movethe entire width-grading linkage. If the bar is pulled far enough a hook 207 formed thereon may be caught on a detent 205, audit the other bar I89 has not already been set in its stopping position it will be pulled to that position by the bar I97. For this purpose the bar I97 carries a lug 208 arranged to engage a lug 265 carried by" the bar I89.

The cutter shaft 49 (Fig. l) is provided with. a grooved pulley 2H] for a transmission belt 2I'I'. An electric motor 2! is supported above the swing frame 23 by the superstructure of the frame I8, and its armature shaft is provided with a cylindrical drum 2 I3 by which the belt is driven. The drum has sufficient length to maintain thedriving connection despite the sidewise shifting of the belt due to the travel of the cutter car-' riage 25.

Having thus described my invention, what I claim as new and desire to secure by Letters: Patent of the United States is:

1. In a copying lathe, a work holder and a model holder constrained to rotation about a turning axis, two feed carriages constrained to paths parallel with said axis, means for moving said carriages oppositely with respect to each other; but with related amplitudes of traverse. swing frames carried by said carriages respectively and constrained to swing about parallel axes transverse to'said turning axis, a cutter and a model wheel carried respectively by said swing frames, and. means connecting said swingframes.

which one pivotal connection of each of said two is coupled with the corresponding one of the other two for dual adjustment to alter the lines of movement of the model wheel and the cutter, and means operable by movement of one of said carriages for imparting adjusting movement to said coupling mechanism.

3. In a copying lathe, feed mechanism including a pair of feed carriages constrained to parallel paths, a pair of links carried by each of said carriages and constrained to swing about parallel axes transverse to said paths, a pair of swing frames each of which is carried by a pair,

of said links, adjustable means carried by each of said carriages to shift one of said axes with respect to the other, a model wheel carried by one of said swing frames and a cutter carried by the other, and mechanism by which said adjustable means are adjusted simultaneously to alter the direction of the lines of movement of the model wheel and the cutter. I

4. In a copying lathe, feed mechanism including a pair of feed carriages constrained to parallel paths, a pair of links carried by each of said carriages and constrained to swing about parallel axes transverse to said paths, a pair of swing frame each swing frame carried by a pair of said links, a model wheel carried by one of said swing frames and a cutter carried by the other, and widthv grading mechanism including two pairs of bellcr'anks movable about fixed parallel axes, two track bars, one for each of said pairs of bell cranks and connecting them in pairs, two parallel links, one for each of said pairs of bell cranks and connecting them in pairs to maintain the track bars parallel with the paths of said carriages,v an adjustable grading link connecting said pairs of bell cranks, means connecting one of said track bars and the cutter swing frame to impart girthwise movements to the latter, and means connecting the model wheel swing frame and the other one of said track bars to render both track bars and both pairs of said bell cranks responsive only to girthwise movements of the model wheel swing frame.

LAURENCE TOPHAM.

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