US3293756A

US3293756A - Drafting apparatus

Info

Publication number: US3293756A
Application number: US417690A
Authority: US
Inventors: Picken William
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-12-11
Filing date: 1964-12-11
Publication date: 1966-12-27
Anticipated expiration: 1983-12-27

Description

Dec. 27, 1966 w. FICKEN 3,293,756

DRAFTING APPARATUS Filed Deo. 1l, 1964 4 Sheets-Sheet vl Dec. Z7, 1966 w. FICKEN 3,293,756

DRAFTING APPARATUS l Filed Dec. ll, 1964 4 Sheets-Sheet 2 INVENTQR.

Dec. 27, 1966 w. FICKEN DRAFTING APPARATUS 4 Sheets-Sheet 5 Filed Dec. l1, 1964 Dec. 27, 1966 w. PlcKl-:N

DRAFTING APPARATUS 4 Sheets-Sheet 4 Filed DeC- ll, 1954 IN VENTOR.

mlm@ .l P w mt' a MIZ United States Patent O 3,293,756 DRAFTING APPARATUS William Ficken, M9232 Peoria Ave., Sun City, Ariz. S5251 Filed Dec. 1l, i964, Ser. No. 417,69) 5 Claims. (Cl. :i3-gil) The present invention relates to drafting apparatus and, more particularly, to a novel drafting machine and cornbination drafting board and drafting machine.

Manyl types of drafting machines are presently availlable for attachment to drafting boards to provide a movable straightedge above the working surface of the board for use as an adjustable guide for drawing straight lines or as an adjustable reference base upon which to support triangles, template-s or other drafting instruments. Although many complex and ingenious drafting machines have been developed to meet the needs of the draftsman, and several types are widely used, all of the previously available drafting machines are subject to one or more weil-known disadvantages. For example, in several popular types of drafting machines the straightedge is mounted on a bulky vertical arm extending downward over the board from the top edge. Such vertical arms, which vary widely in design, for example, include boardlike members several inches wide and rigid bar members with associated tensioning cables. Arms of these types are generally mounted to be movable from side to side over the surface of the drafting board parallel to the upright sides thereof. Another type of arm in common use consists of a bar and cable structure having two joints separated by an intermediate elbow-like articulation. Arms of this type are generally mounted by rotatably affixing the upper end to the top of the board so that the lower end of the arm, to which the straightedge is attached, is adapted to be moved upward and downward and from side to side over the surface of the board. The se-veral foregoing types of vertical arms and others similar in structure and purpose, have the disadvantage that they overlie the board and, due to their bulk, seriously interfere with the draftsmans access to the drafting surface.

Other less complex drafting machines are also available in Which a straightedge disposed parallel to the horizontal edges of the board is attached at each end to an endless traveling cable. The traveling cable -at each end of the board is carried by a pair of wheels one of which is rotatably mounted at the top and one at t.e bottom of the adjacent vertical side of the board. The straightedge, while remaining parallel to the horizontal edges of the board is movable upward and downward over the drafting surface in a direction normal to the horizontal edges of the boa-rd. Drafting machines of this type, while having the advantage that the obscuring arm is obviated, are subject to the disadvantage that the straightedges do not provide a reliable reference base. This is due to the fact that the traveling cables permit the straightedge to sway undesirably from side to side on the board.

All of the available drafting machines described above also have the serious disadvatage that they require counterweights of various types to permit their use when the drafting board is tilted at an angle of more than to from the horizontal. Inasmuch as it is generally necessary to tilt the drafting board at an angle of about 15 to 85 in order to provide comfortable access to the board, particularly if the draftsrnan is to Work in a sitting position, it is obvious that the use of cumbersome and diflicultly adjustable counterweights is necessary with available drafting machines under virtually yall normal use conditions.

Therefore, it is an object of the present invention to provide drafting machines and combination drafting Mice boards and machines having improved -access 4to the drafting surface.

It is another object of the invention to eliminate the bulky vertical arms of previously available drafting machines.

It is still another object of the invention to eliminate the traveling cable of previously available drafting machines.

It is another object of the invention to provide a d-rafting machine having a horizontally disposed straightedge which is not subject to side sway i.e. movement in the direction of its long axis.

It is yet another object of the invention to provide a combination drafting board and machine having a horizontally disposed straightedge which is movable upward and downward over the drafting surface but which is adapted to remain where placed, irrespective of the forces of gravity, and to be locked in any desired position.

lt is another object of the invention to provide a combination drafting board and machine wherein the board is in the form of a rectangle having a long axis and a short axis, means for supporting the board in Working position with either the long axis or short axis thereof disposed vertically as desired, and straightedge means adapted to be disposed in a horizontal position over the board when it is arranged with either the long or short axis vertical.

It is still another object of the invention to provide a combination drafting board and machine including means for adjustably supporting the board at any desired working angle from about 15 to 85 from the horizontal and wherein the drafting machine is operable with the board positioned at such angles without the use of counterweights.

It is yet another object of the invention to provide a combination drafting board and machine whe-rein the board is faced with a synthetic plastic material capable of receiving and holding a compass point without slipping and which is also adapted to hold a sheet of drafting paper or the like thereagainst by electrostatic attraction.

It is another object of the invention to provide a combination drafting board and machine wherein the horizontal and vertical edges of the drafting surface of the board are provided with graduated scales and where-in the straightedge is also provided with a graduated scale, the graduations of which correspond to the graduations on the edges of the drafting surface of the board parallel to said straightedge, whereby all measurement reference points move with the movable straightedge thus obviating repeated reference to the graduated scales at the edge of the board.

The above and other objects of this invention will be understood from a reading of the following description of an embodiment thereof as shown in the accompanying drawings in which:

FIG. l is a top plan View of a combination drafting board and machine of the invention showing a movable straightedge disposed horizontally and parallel to the long axis of the board;

FIG. 2 is an elevational vie-W of the board resting on a horizontal surface and showing the long side of the board which is uppermost in FIG. l;

FiG. 3 is a cross sectional view through a. roller assembly forming part of the drafting machine taken on the line 3--3` of FIG. l;

FIG. 4 is a cross sectional view of the roller assembly taken on the line 4-4 of FIG. 3 and showin-g a portion of the track on which the roller assembly runs;

FlG. 5 is another cross sectional view of the roller assembly taken on the line 5-5 of FIG. 4;

FIG. 6 is a cross sectional view of the roller assembly taken on the line 6 6 of FIG. 4;

feg, es

FlG. 7 is a bottom plan view of thedrafting board and machine showing the arrangement of brackets for attachinent of meansl for' 'supprting the board in working posinon;

FIG; Slis a side elevational View showing the drafting board and machine of FIG. 1 mounted in two different positions on adjustable support means;

IFIG. 9 is a view partly in section of a supporting bracket taken along the line 9 9 of FIG. 8 and showing an instrument tray mounted on said bracket; and

FIG. l0 is across sectional view of means for attaching the board to the support struct-ure taken along the line 10516 of FIG. 8; l

Similar characters of reference are employed in the above described views, to indicate ycorresponding parts.

Referring to the drawings, the reference character 1? indicates the drawing board of the combination drafting 'board and machine. Said drawing board is rectangular in shape', having two parallel lo-ng Isides and, at right angles thereto, two parallel short sides. The top surface of the board 1@ has bonded thereto a thin layer of a suitable thermoplastic material which provides a smooth drafting surface 11. The drafting surface 11 is hard to the touch but is ladapted to accept the point of a compass or other drafting instrument without slippage and is also charac-` terized by having electrostatic attraction for paper and other sheet materials used by idraftsrnen. For this reason a sheet of paper or the like may be spread on the surface 11 and smoothed out with the hand or a straight edge so that the paper will adhere t'o the surface 11 s-ufciently to permit the draftsman to work without the use of thumb tacks or tape to hold the work in place. However, when the work is finished, the paper is easily removed by simply lifting a corner of the sheet and peeling it off the surface 11. The edges of the drafting surface 11 of the board 10 are provided with suitable graduated scales as shown in FIG. 1.

A straightedge member 12 .composed of a transparent plastic material is mounted for movement upward and downward in sliding contact with the drafting surface 11 with its upper and lower straight edges parallel to the long sides of the board. Another shorter straightedge member 12 (not shown) is also provided for alternative use mounted parallel to the short sides of the board 10 when it is desired to use the board with its long axis upright rather than horizontal as shown in FG. 1.

The straightedge member 12 is mounted on the board 10 'by attachment of each end to a roller assembly by means of a bolt 13, the threaded end of which bolt extends through a bore hole located on the yaxis and near the end of the straightedge member 12. A washer 14 is placed on the end of the bolt 13 protruding through the hole in straightedge 12 and the assembly is secured by means of a knurled, internally threaded nut 15 screwed on to the end of bolt 13. Each end of the straightedge 12 is thus rmly secured in a bedding channel provided therefor in each roller assembly as |best shown in FIGS. 5 yand 6.l

The two roller assemblies, which are identical except that that each is the mirror image of the other, are mounted at opposite sides of the board on tracks 16. The tracks 16 are metal members having an angular C-shaped cr-oss section consisting of two

legs

17 and 18 joined at a 90 angle to ian intermediate base 19. The plane of the base 19 lof each track 16 -is disposed parallel to the plane of the side, and normal to the surface 11 of board 10. The planes of the

legs

17 and 18 are parallel to the plane of the drafting surface 11 of the board. Each of the C-shaped tracks 16 is fixed to the board with its leg 17 spaced from the back of the board. The other leg 18 is nested lin the edge of (the upper surface of the board 10, which is suitably cut away for this purpose las shown in FIG. 3 so that the upper surface of the leg 18 is ilush with the upper surface of the board beneath the plastic drafting surface 11. The exterior surface of base 19 and the inner edge 20 of leg 17 of each track 16 function as bearing surfaces on which the roller assembly moves.

track 16 is similarly mounted on each of the four sides of the board; the ends of adjacent tracks meeting at the corners of the board being mitered at a 45D angle as shown in FlG. 7. The four angular C-snaped tracks 16 thus form a frame for the board and since they are of metal serve to protect the sidesof the board from dam-age.

The roller assemblies include a roller housing consist ing of a top plate 21, a bott-om plate 22 and a pair of channelshaped end plates 23 which form a box-like structure open on two sides. A pair of guide plates 24 are fixed to the top plate 21 in spaced apart relation to form the bedding channel -in which the end of a straightedge member 12 is accommodated. A relatively large diameter main roller 2S of substantial thickness is mounted for rotation within the roller housing on bolt 13 which passes through an axial bore hole in the roller. The bolt 13, which functions as a stationary axle for the main roller 25, has an enlarged head with a at lower surface. The bolt 13 passes through a bore hole in 'bottom plate 22 of the roller housing and is fixed thereto by means of nut '.26 threaded thereon to pull the hat under surface of the enlarged hea-d of the bolt tightly against the plate 22. The other end of the bolt 13, vwhich extends thro-ugh bore holes in top plate 21 and straightedge member 12, and protrudes therefrom, is secured 4as described above by washer 14 and knurled nut 15 threaded thereon;

Each roller assembly is provided with a slide plate 27 one end of which is iixed to bottom plate 22 of the main roller housing by bolt 13 and nut 26. The other end of the slide plate 27 extends beyond the plate 22 in a direction normal -to the bolt and inboard of the roller 25. The protruding end Iof the slide plate 27 is adapted to slide into a slot ina slide block 281; the slot and slide plate being correspondingly dimensioned to provide a close sliding lit therebetween. The slide block 2S is made up of a bottom plate 29 and a top plate 3G suitably fastened together. The bottom plate 29 has a cut-out channel in its upper surface which when covered by the top plate 30 provides the aforementioned slot which extends through the slide b-lock. A pair of auxiliary rollers 31 are rotatably mounted above the top plate 30 of the slide block in spaced apart relation by the use of bolts 32. Each of the bolts 32 extends through an axial hole in one of the auxiliary rollers 31 and through vsuitable holes in the

plates

29 and 30 of the slide block; the protruding end of the ibolt in each case being secured by a nut threaded thereon.

The position of the slide plate 27 within the slot in the slide block is adjust-able and may be locked at a desired position. This is accomplished by the use of a pair of knurled head set screws 33 having a conical apex iat the end opposite the knurled head Ias best seen in FIGS. 3 and 6. Two internally threaded bore holes, located in the channel of the slide block with their centers on a line normal to the axis of the main roller 25 extend through the bottom plate 29 to receive the `set screws 33. Corresponding bore holes extending through the slide plate 27 have conical countersunk orices on the under side of the plate to receive the correspondingly shaped conical ends of the set screws 33.

Thus the roller assembly consists of two separable units, one consisting of the main roller 25 with its housing and protruding silde plate 27 yand the other consisting of the slide block 28 carrying the auxiliary rollers 31. The bore holes in the bottom plate 29 of the slide blocks and in the slide plate 27 are located so as to be in axial alignment when the Set screws 33 are screwed into said bore holes to the fullest possible extent. In this condition the auxiliary rollers 31 are disposed at a predetermined distance from the main roller 25. This distance between the main roller 25 and the auxiliary rollers 31 is such that when the roller assembly is mounted on a track 15 and the set screws 33 are turned up linger pressure tight, the main roller 25 is held firmly against the exterior flat surface of base 19 of the track and the auxiliary rollers 31 are also held firmly against the narrow inboard edge 20 of leg 17 of the track. When the set screws 33 are thus tightened in the bore holes in the bottom plate 29 of the slide block and the countersunk holes in the lower surface of the slide plate 27, the clamping pressure of the

rollers

25 and 31 on the track 16 is such that the roller assemblies on either side of the board 1t) and the connecting straightedge member can be rolled upward and downward on the board only by strong manual force.

The amount of force required to roll the drafting machine upward and downward on the board can be reduced by lessening the clamping pressure of the rollers against the track. This is accomplished by simply unscrewing the knurled set screws 33 slightly thus partially withdrawing the conical points of the set screws from the conical countersunk orifices of the bore holes in the slide plate 27. When this is done the point of the conical end of the set screw 33 is no longer closely confined by the complementary point of the countersunk recess in the underside of the slide plat-e 27 thus permitting slight relative movement between the slide block and the slide plate. This slight displacement of the slide block increases the distance between the main roller 25 and the auxiliary rollers 31 thus reducing the clamping pressure on the track and permitting movement of the drafting machine over the board with less effort. lt will be seen, therefore, that any desired degree of ease of movement of the drafting machine can be achieved by simple adjustment of the set screws 33.

A brake assembly is provided for locking the drafting machine in a desired position. This asembly consists of a brake member 34 mounted adjacent to the main roller 25 inside the roller housing. The brake member 34 is fixed to a knurled headed set screw 35 the threaded shaft of which extends through an internally threaded bore hole in the end plate 23 of the roller housing. When it is desired to lock the drafting machine in a selected position the set screw 35 is manipulated to force the brake member 34 against the roller 25 thus effectively preventing travel of the roller assembly on the track 16. When it is desired to shift the position of the drafting machine once again the brake is released 4by unscrewing the set screw 3S to withdraw the brake member 34 from contact with the roller 25.

The combination drafting board and machine is provided with suitable means for supporting the board in substantially any desired working position. Four short rubber-tipped legs 36 are fixed to the back surface of the board as best seen in FIGS. 2 and 7 for use in supporting the board on a fiat surface such as a table top. The legs 36 are positioned inboard from the sides of the board t0 prevent interference with the roller assemblies and are dimensioned to provide sufficient clearance between the roller assemblies and any fiat surface on which the board is placed to permit use of the drafting machin-e.

The combination drafting board and machine is also provided with detachable means for adjustably supporting the board at any desired angle from about to 85 above a horizontal surface such as a table top. This support means consists of a pair of adjustable structures one of which is detachably mounted inboard of and parallel to each of the short sides of the board, for example, when the board is to be supported with its long axis horizontal. Each of the detachable support structures consists of a base member 37 having a rubber cushioning member 38 fixed to the underside near each end. Each base member 37 has an upstanding bracket 39 fixed thereto near one end and an adjustably extensible arm 4@ rotatably fixed to the other end. The extensible arm 4t? includes an elongated hollow tube-like member of rectangular cross section and an elongated extensible member slidably fitted in said tube. A threaded bolt is fixed to the lower end of the inner extensible member of the arm 40 so as to protrude through a longitudinal slot in the upper side of the elongated tube-like member. The overall length of the extensible arm 40 is adjustably set by lplacing a washer over the bolt on the inner slidable member and threading a knurled cap nut 41 onto the end of said bolt. When cap nut 41 is turned down finger pressure tight the inner and outer slidable members of arm 40 are held against sliding contact, thus effectively locking the extensible arm at the desired length.

The two adjustable support structures are attached to the back of the board by first engaging a pin at the upper end of bracket 39 in a key-slotted mounting bracket 42 fixed to the back of the board near the lower corner at one side. The upper end of the extensible arm 40 is then fitted between the upstanding sides of a mounting bracket 43 fixed to the back of the board on the same side near the upper corner. A knurled headed, threaded pin 44 is then screwed into an internally threaded hole extending through the bracket 43 and arm 40.

When an adjustable support has been mounted on each side of the board in this manner the tilt or angle of the board is adjustable from about 15 to 85 when the base members 37 are placed on a horizontal surface such as a table top. The angle of the board is, of course, determined primarily by the length of the extensible arm 40. When arm 40 is fully telescoped as shown in full lines in FIG. 8, the board is disposed at an angle of about 15. To increase the slope of the board to any desired angle up to about tne knurled caps 41 are loosened, the board raised to the desired angle by extension of the arms 4i), and the cap nuts 41 tightened again to lock the board at the desired position. Such an elevated position is shown in bro-ken lines in FIG. 8.

An upstanding bracket 39 of the support structure is provided with a rectangular cut-out 45 in each side of the bracket to receive the shaft 45 supporting an instrument tray 47 which is provided to hold the draftsmans tools, pencils, erasers, ink and the like.

As noted previously, the combination drafting board and machine of this invention is adapted to be used with either the long or short axis of the rectangular board in an upright position. Therefore, two sets of mounting brackets are fixed to the back of the board for attachment of the adjustable support structure. Referring to FIG. 7, it may be seen that the

brackets

42 and 43 on each side of the board connected by the lines a-a are employed to mount the board with its long axis horizontal. The

brackets

42 and 43 connected by the lines b-b, on the other hand, are employed to mount the board with its long axis vertical.

It will -be apparent from the detailed description above of an embodiment of the present invention that the new drafting machines and combination drafting boards and machines obviate many of the disadvantages of the prior art devices. For example, inasmuch as the roller assemblie-s are mounted completely outboard of the drafting surface of the drawing board, the draftsmans access to that surface is maximized; the onl element present on the drafting surface being straightedge member which is a drafting tool. The new drafting machines also eliminate the need for the bulky vertical arms of previously available machines. Moreover, inasmuch as the side mounted traveling cables of the prior art have been eliminated and the straightedge member is firmly mounted -between two unyiel-ding roller assemblies, the straightedge is not subject to side sway and thus provides a dependable scale of reference points along its axis. Still further, provision for adjustment of the resistance to movement of the straightedge member by the use of easily manipulated set screws permits setting of this resistance so that the straightedge will remain where placed on the board despite the force of gravity at any desired working angle of the board. This leaves both of the draftsmans hands ree for the manipulation of instruments. The provision of the brake device also permits the straightedge to be anchored at a desired position as a reference base for any desired period of time and yet per-mits it to be readily shifted to a new position `by simply releasing the brake.

Still another major advantage of the new drafting machine is that it can be used on a board disposed at any desired working angle without the use of cumbersome and difficulty adjustable counterweights.

Another unique advantage of the drafting board and machine shown in the accompanying drawings is that it provides the convenience of traveling reference points, i.e. inasmuch as the straightedge member is graduated with a scale identical to and in vertical registration with the scales on the parallel edges of the drafting surface, it is in effect a moveable extension of these scales. Therefore, when it is necessary to move the straightedge upward or downward over the board to Work at a new location, all of the reference points move with the sltraightedge and the draftsman is not required to refer to the edge of the boardv -but may@ take his reference directly from the straightedge member.

Not the least of the advantages of the new drafting apparatus is its simplicity of manufacture and assembly which makes it substantially more economical than comparable apparatus previously available.

Although the invention has been described in detail in connection with a specific em-bodiment thereof shown in the drawings, this embodiment is merely illustrative of others that will be apparent to those skilled in the art and is not to be construed as limiting the scope of the invention which is defined in the accompany claims.

I claim:

1i In a drafting machine, which when in use is -mounted on a board having a planar drafting surface and at least two opposite and parallel straight sides, comprising two roller means to roll along the opposite sides of the board as a track, one roller on each side, and an elongated straightedge means extending between and connected at each end to one of said roller means, whereby sai-d straightedge means is mounted in sliding contact With the drafting surface of such a Iboard for movement thereover in a direction normal to the long axis of the straightedge means, the improvement which comprises an auxiliary straight track means mounted on the board spaced from and parallel to each of said opposite sides, and wherein :said roller means each include a main roller and at least one auxiliary roller spaced therefrom, said roller means being moveably mounted on the -board by clamping engagement between said main roller disposed in rolling contact with one of the opposite sides of the board and an auxiliary roller disposed in rolling contact with said auxiliary track.

2. A drafting machine'according to claim 1 having means for adjusting the clamping force of said roller means.

3. A drafting machine according to claim 2, wherein the means for adjusting the clamping force of said roller means comprises a slide plate connected to and prof truding from said main roller, a slide block connected tol said slide roller and having a channel therein to receive said slide plate, a set screw having a conical apex, said set screw extending through and in threaded engagement with said slide block, and an orifice surrounded -by a conical countersunk surface in said slide plate, said set screw being positioned with its apex adjacent to `said orifice in the slide plate, whereby on turning the set screw in one direction its apex is advanced into said orifice and into contact with said countersunk conical surface and on turning the set screw in the opposite direction the apex thereof is withdrawn from said orifice, said contact between the apex of said set screw and said conical countersunk surface causing said slide plate to move in said channel with respect to said slide block, thus changing the distance ybetween said -main roller and said auxiliary roller, whereby the clamping force of the roller means is adjusted.

fl. A drafting machine, adapted to be mounted on a board having a planar drafting surface and at least two opposite and parallel straight sides, which comprises in combination, a pair of roller means, one of said roller means being adapted to be mounted to roll along each of the opposite and parallel sides of a Iboard as a main track, auxiliary straight track means adapted to -be mounted spaced from and parallel to the two opposite and parallel straight sides of a board, and an elongated straightedge means connected at each and thereof to one of said roller means, said roller means each including a main roller and at least one auxiliary roller, said roller means being moveably mountable by clamping engagement between said main roller disposed in rolling contact with a slide of a board and an auxiliary roller in rolling contact with said auxiliary track. with said auxiliary track.

5. A drafting machine according to claim 4 having means for adjusting the clamping force of said roller means.

References Cited by the Examiner UNITED STATES PATENTS 611,697 10/1898 Lundy 33-76 1,270,609 6/1918 Ezra. 1,440,993 l/ 1923 Hasbrouck et al. 2,627,323 2/1953 Larson 33--76 X 2,805,479 9/1957 Droste 33-80 2,874,474 2/1959 Eeele et al. 33--76 2,954,609 10/1960 Goertz 33-80 LEONARD FORMAN, Primary Examiner.

HARRY N. HAROIAN, Assistant Examiner.

Claims

1. IN A DRAFTING MACHINE, WHICH WHEN IN USE IS MOUNTED ON A BOARD HAVING A PLANAR DRAFTING SURFACE AND AT LEAST TWO OPPOSITE AND PARALLEL STRAIGHT SIDES, COMPRISING TWO ROLLER MEANS TO ROLL ALONG THE OPPOSITE SIDES OF THE BOARD AS A TRACK, ONE ROLLER ON EACH SIDE, AND AN ELONGATED STRAIGHTEDGE MEANS EXTENDING BETWEEN AND CONNECTED AT EACH END TO ONE OF SAID ROLLER MEANS, WHEREBY SAID STRAIGHTEDGE MEANS IS MOUNTED IN SLIDING CONTACT WITH THE DRAFTING SURFACE OF SUCH A BOARD FOR MOVEMENT THEREOVER IN A DIRECTION NORMAL TO THE LONG AXIS OF THE STRAIGHTEDGE MEANS, THE IMPROVEMENT WHICH COMPRISES AN AUXILIARY STRAIGHT TRACK MEANS MOUNTED ON THE BOARD SPACED FROM AND PARALLEL TO EACH OF SAID OPPOSITE SIDES, AND WHEREIN SAID ROLLER MEANS EACH INCLUDE A MAIN ROLLER AND AT LEAST ONE AUXILIARY ROLLER SPACED THEREFROM, SAID ROLLER MEANS BEING MOVEABLY MOUNTED ON THE BOARD BY CLAMPING ENGAGEMENT BETWEEN SAID MAIN ROLLER DISPOSED IN ROLLING CONTACT WITH ONE OF THE OPPOSITE SIDES OF THE BOARD AND AN AUXILIARY ROLLER DISPOSED IN ROLLING CONTACT WITH SAID AUXILIARY TRACK.