US2810962A - Ellipsographs - Google Patents

Description

Oct. 29, 1957 A. J. MEYER ET AL 2,810,962

ELLIPSOGRAPHS Filed March 5, 1957 5 Sheets-Sheet 1 /s 27 29 32 '42 4/ 4o 3o 2a Oct. 29, 1957 A. J, MEYER ETAL 2,810,962

ELLIPSOGRAPHS :s sheets-@wb2 Filed March 5, 1957 Oct. 29, 1957 A. J. MEYER ET AL 2,810,962

ELLIPSOGRAPHS 5 Sheets-Sheet 5 Filed March 5, 1957 United States Patent ELLIPSOGRAPHS Andre J. Meyer, Rocky River, and Andre J. Meyer, Jr., Elyria, Ohio Application March 5, 1957, Serial No. 644,028 11 Claims. (Cl. 33-31) This invention relates generally to ellipsographs, or implements to scribe or draw ellipses.

Many ellipsographs have been proposed, but none have `achieved broad acceptance, because most of the devices suggested for the pur-pose are either cumbersome and expensive or are inaccurate, slow, hard to operate or of limited usefulness.

AIt is an object of this invention to provide an inexpensive ellipsograph capable of rapidly tracing ellipses 'of any desired proportion .and size between a point and the maximum `size circle for which the instrument is designed.

It is -a further object to provide an ellipsograph operating with a maximum of ease and mathematical precision.

Another object -is to provide means capable of cooperation with existing drafting machines, so as to temporarily convert them into large scale ellipsographs, without impairing their normal function.

The construction necessary to accomplish these 'objectives will .be explained by reference to the appended drawings, in which:

Fig. I is a plan view of an ellipsograph incorporating the invention.

Fig. Il is `a bottom elevation partially in section along the line lI-II -of Fig. 1.

Fig. III is a section along the line III-III of Fig. I.

lFig. IV is a section also along the line III-III of Fig. I, but showing -an ink pen installed instead of a lead pencil.

Fig. V shows the adaptation of the invention to a conventional drafting machine.

Fig. VI is a section along the line V'I-VI marked in drawing V.

Fig. VII is a reduced scale drawing `of :a drafting hoard, upon which a drafting machine with the ellipsograph attachment of Fig. V are installed.

Fig. VIII represents a graphical construction `for an ellipse, which will rbe used to illustrate the theory of the invention.

Fig. IX is the plan view of 'an alternative construction.

Fig. X is 'an enlarged section along the line X-X of Fig. IX.

Referring to the drawings in which similar reference characters designate similar parts throughout, the ellipsograph of Fig. I lcomprises a rectangular base plate 1, upon which the elements of the ellipsograph are mounted. Preferably it is made out of cellulose acetate ora similar transparent plastic. It is locally reinforced by the blocks 2 and 3 fastened to it by means of rivets, screws or glue, for the purpose of mounting the clevis pins 4, 5 and 6 which are pressed into the reinforcements. On the pivot pin 4 a hollow spindle 7 lcan revolve freely. On it are mounted -a circular disc 8, a spacing washer 9, another circular disc and an indexing washer 11. The outer end of the spindle 7 has a threaded portion 12, which screws into the knob 13. When this knob is tightened, the spindle 7 and all the parts 8, 9, 10, 11 and 13 rCC ybecome a unit assembly, referred to as the disc assembly, which may be installed onto pin 4 and rotated with re spect thereto.

The discs 8 and 10 are preferably also made out of plastic. They have been provided with a slot 14, which engages the ilat `side 15 milled on the spindle. `In Fig. I the yleft hand side `of the knob has `been omitted to show this at 15, it being understood that the right hand side of the spindle is `fashioned in 'the same manner. This View shows that also the washer 11 engages the flat yso that Ineither the discs, nor the washer can revolve with respect to the spindle, even if the knob ywere not tightened completely.

The -discs -8 and 10 `are shown eccentrical'ly mounted with respect to the centerline of the pivot pin 4. The amount of eccentricity can 1be read off at the mark 16 on the washer 11, which is -beveled t-o facilitate reading at the graduated scale indicated at 17. When the Zero on the graduations is lined up with the -mark 16 on the washer 11, the `disc will be exactly concentric with the pin 4. In the drawing disc 10 is shown installed with more eccentricity than disc S, but it must be understood that either disc may be adjusted with any desired eccentricity. If the ellipse to be drawn is to have its major axis in a vertical direction, disc 8 would be `adjusted with the larger amount of eccentricity.

A second unit assembly is shown generally at 21. It has the form of a square and consists of 2 pairs of strips of plastic 22a, 2213, 23a and 23h, 'separated by spacers 19 at the corners in such a manner that the opposite sides are in the same plane. The strips and spacers are glued, riveted or fastened together by means of screws in such a lmanner that the strips 22a and 22b are parallel, perpendicular to the strip 23a, and a distance apart equal to the diameter of the disc while the strips 23a and 23b are parallel and a distance apart equal to the diameter Iof the disc 10. To facilitate mounting the disc assembly on pin 4 and inside the square, the lower disc 8 is preferably made slightly smaller than the upper disc 10. Further the thickness of the spacer 19 is equal to that of the washer 9 and that `Of the strips equal -to that of `the discs, so that it will :be possible to adjust the length kof the pins or 'feet 24 lin such a manner that the upper .and lower surfaces of the strips Acorrespond to the upper and lower surfaces yof the discs. In this manner the -disc 8 will Ibe in contact with the edges 18a and 18b of the strips 22a and 22b, while the `disc 10 contacts the edges 20o and 2Gb of the strips 23a and 23h.

The movement yof the square is constrained to permit translation in any direction lwith the :pins 24 sliding over the base plate or drawing paper underneath it, as the case may he, but rotation is prevented. Thus, no matter how the square moves, the ledges 18 and 20 will remain parallel to their -original position and in contact with the discs 8 and 10. This constraint is obtained as follows:

Two identical links 25 and 26 are arranged to pivot around the pins 5 and 6 and secured thereto yby means of suitable washers 40 and gnipor .snap rings 41. At their other kextremity they may pivot around the pins 29 and 30, which are pressed into the floating plate or knee piece 31. The distance 29-30 is equal to the distance between the pins 5 and 6. Thus the pins 5, 6, 29 and 30 are .always at lthe vcornerp'oints of a parallelogram and since the side 5-6 thereof is fixed, the side 29-30 is free to swing, 'but it must always remain parallel to the `side 5 6. Thus the knee 31 cannot rotate. The plane in which it moves is further determined by the length of the pin 42 in such a manner that lits upper surface coincides with the plane of the upper `surface of strip 23 and of the disc 10. Spacers 27 and 28 are used to maintain the links 25 and 26 in a plane parallel thereto.

Yto mount a scriber.k In Fig. I the 3 At lall ends the same washer and grippingV combination secures the links.

In the knee piece 31 twoy additional pins 32 and 33 are pressed, in such a manner that the'direction 32-33 Y 'is perpendicular to that of 29-39. The links 34 and 35 can pivot around these pins 32 and 33, while their other extremities may pivot around the pins 36 and 37, which are pressed into the corners of the square parallel to all other pivot pins. The distance Ybetween 36 and 37 is equal to the distance between'32'and 33.

` Thus the pins 32, V33, 36 and 37 are again at the cornerpoints of aV parallelogram having one side 32-33,con strained to remain'perpendicular toY 29-,30,1hence to `5 6; Evidently the square is free to move in all directions, but it cannot rotate.

To operate the device the discs 8 and l0. are first adjusted so that their eccentricities are respectively equal to the vertical and horizontal half axes of the desired ellipse. After tightening the knob, the disc assembly is entered inside the square and mounted on the pin 4. AfterV this the knob is given one orj more rotations in either direction. As is demonstrated below each Ypoint of the square willV describe theV desired .ellipse during this rotation, therefore any point on it may be used upper left corner f thersquare is used for this purpose.

Fig. III shows a section through a scriberadapted to the use of pencil lead. A bushing 38 is pressed into a suitable opening bored in the Vsquare assembly. The pencil guide 39, made to have' a sliding fit in the bush- "ing bore, is inserted therein and locked by means of the screw 43. This pencilguide has a central hole into which a standard lead 44 can be insertedwith a sliding iit. The Weight 45 can be slipped'over the outside of the pencil guide. In itis a split collet46, which after tightening of the nut,47, grips Vthe lead 44 and locks it tight. Thus the weight, collet, nut and lead form a tight assembly that may bereadily inserted or `withdrawn from Vthe pencil guide. `The Weight 45 is proportioned so as toV exert suicientjpressure on the pointV 43V of the lead to provide'a satisfactory black line on the'` paper. Fig. IV shows how a standard inkwell type of a pen 48a Vmay beV inserted in the bushing 38 Vand locked with the screw 43. Obviously any other scriber may be used, such as a brass rod for scribing on steel instead of paper and the device could even be proportionedl so as to guide a cutting tool ortorch in an elliptical path.

VThe position of the'square, hence of the scriber, in

Fig. I corresponds to the upper end oftheV vertical axis of the ellipse, because the disc S is in its top dead center. VTherefore a vertical line drawn through the centerof the scriber is this vertical axis and the side 49 of the base 1 runsparallelthereto at a xed distance A. The horizontal axis of the ellipse to bei traced is a horizontal line drawn at a distance below the scriber point equal to the eccentricity of disc S. This axis istat a distance B vfrom the side Y50 of base 1. The distances A and B are invariable,` which may be veried by adjusting both discs 8 and 10 to zero eccentricity. This puts the scriber exactly at the intersectionof the two axesof the ellipse.. t e' i V1 with these lines, which puts thefinstrument in kthe exact location needed to locate the ellipse correctly. Henow fixes Vthevbasell byY `means of tape, thumb'tacks YYor-otherV means-in this position, adjustsY the disc Vassem-l bly and traces the curve. e f

-It is to be noted that Vthe strips V22a andi 23a` could be `'omitted if a spring were used to urgeY the edges 1Sb and 2017 in contact with the discs 8 and 10. In that case 4 Y the scriber would have to be mounted'on-an extension of either the strip'22b or 2317. Such a design was actually constructed and tested, but it Was found diili'` cult to operate and to produce inaccurate results because of the variable torque, friction and dellections in the mechanism, all caused by a spring less than two ounces of tension.

It is further to be noted that the knee piece 31 has only one degreeof freedom, this is: only one dimension is necessary to completelyV determine its position. Such a dimension could be the angle of rotation of the link 26 with respect to a vertical line through Vthe center of pin 6, or it might be the distance of the center of pin to the side 49 of the base, Vor any other such dimension. Furthermore each point of the knee travels on an arc with a radius equal to the length of the links 25 orlo.

It Visrfurther to be notedrthat the square 21 hasftwoV degrees of freedom so that two dimensions Vrnustlae given to determine .its position. These might` be the coordinates of the center of the square, or any other point thereof, with respect to any system of axes, or any other arbitrary pair of dimensions. Thus the square has freedom of translatory movement in aplane, but not of rotation.

' Conversely any other means controlling the movement of a square, as described,'to permit its translation Vin a plane without permitting its rotation, will be suitable for the construction of an ellipsograph conforming this invention. As an example the well known drafting machine shown in Fig. VII constrains two perpendicular scales for this type of motion. Therefore if a square substantially as describedwere attached to the scales 51 and 52 or the scale bracket 53, only a disc assembly and its pivot pin 4 Vare needed to construct anY ellipsograph of the type described, provided the discs vare made to lit the square and register with the proper edges 18 and 20 thereof. As has already been mentioned above the discs do not haveto be equal in diameter, therefore a rectangle could be used, although this would limit the vertical and horizontal axes unequally.

Fig. V shows how a square, constructed as described disc assembly previously described Vin `connection with f YKIn Fig. I the distancesvA andV B are both equal to Fig. I.

Since the scales 51 and 52 are provided with excellent graduations, the adjustment ofthe disc assembly may Vbe simplified. For this purpose a pin 56, of the same proportionsk as the :pin 4, is installed Von top of the 'strip 23a. VThe Vdisc assembly is mounted thereon'with both discs approximately in the concentric position. Next the disc, which is to have the Ysmallest leccentricity, is moved to the right until the scale reading at its periphery" corresponds to the desired eccentricity. This `operation is repeated withthe rothendisc. after which theV knobV is tightened'. Next the base plate 1 is installed in the proper .location bylining up its edges 49 and 50 with Vthe |lines already drawn on the .paper at constant distances from the center of the ellipse and after securing the base plate to the drawing, the disc assembly is introduced into the square and mounted on .theV pin 4. When the scriber is inlposition, one turn sired ellipse. Y

- The ellipsographshown ingFigs. IX and X differs from f rther one of Fig. I only Yin someconstruction detailsA and -inthe method Vof adjusting the eccentricty ofthe-discsY S and 10 with i'espect to the spindle 7.

of the knob13 will produce the de-Y The square Z1 is made out of a single at sheet of metal, having an internal square opening, the sides of which have been formed by bending part of the metal to make an angle of 90 with the plane of the sheet. Fig. X shows how the lips Zlla and Zlib have further been provided with ilanges 57, so that the periphery of disc 10 may contact the inner surfaces of the lips and the disc be prevented from moving in the direction of knob 13 by the flanges. ln the same way llips 18a and 18h are formed by bending part of the metal in the opposite direction to provide lips having surfaces and anges 58 to encase disc 8.

After the discs have been assembled to the square 21, the washer 9 is installed, to separate them from each other. The ats i5, milled on the spindle 7 in the constructions of Fig. I and Fig. V, have been machined on this washer and consequently the discs must be sprung slightly to permit the assembly of the washer 9. Once this washer is installed, the discs can no longer be independently moved to any arbitrary position within the square, the centers of the discs 8 and 10 and of the washer being compelled to remain in the same plane because or" the flats on the washer.

The spindle 7 may now be inserted through the hole in the washer, after which the knob assembly is mounted and held in place by means of the special nut 59, engaging the threaded portion 12 on the spindle 7.

The knob assembly consists `of a Ilower shell 60, carrying two screws 6l and a cover 62. Nuts 63 hold the two shells together against the action of the springs 64 and 65. The upper spring 64. acts via the washer 66 on the sleeve 67 and reacts directly on the cover 62. The shoulder 68 on this sleeve is in contact with the lower shell 6ft before the knob is installed. The lower spring 65 acts directly on the lower shell 6i) and reacts on the cover 62 via the bushing 69.

After installing the knob assembly on the spindle 7 and securing it by means of the nut 59, the lower end of the sleeve 67 will be in Contact with the washer 9 and the shoulder 68 will be free from the lower shell 60, so that the upper spring is compressed a little more. The load ot this spring therefore serves only to clamp the lower disc S between the washer 9 and the ange 7G of the spindle 7.

if the nuts 63 are now loosened up, the lower spring 65 transfers its load via the shell 6i) to the disc 1i). This load is transferred through the disc 10 to the washer 9, to the disc S and through disc S to the tlange 7 i). Therefore disc lo is subject to an axial clamping force equal to the load of the lower spring 65 and disc 8 to a force equal to the load of both springs. Since both springs react on the cover 62, the latter reacts on the nut 59 with the same force as is applied to flange 70 and the spindle is loaded iu tension by the force of both springs.

if next the nuts 63 are tightened again, the iirst effect will be disc lil comes free so that its eccentricity may be altered. Further tightening of these nuts will also free disc S for radial movement.

ln Fig. l the motion of the square was constrained by the use of four links, positioned so as to form two parallelograrns, one between tie base plate and a knee piece and anot ier between the latter and the square. In Fig. iX the same principle is used in a somewhat different manner by combining the functions of pins 29 and 32 Fig. l into a single pin and those of pins 3@ and 33 into another single pin. As a result the knee piece 31 of iX has become a straight link `of a length equal to re distance between the pins and 6 which in turn was made equal to the distance between the pins 36 and 37, attached to the square 21.

One other modification to be noted in X is the construction of the scriber to be used when scribing on vertical surfaces, where the weight 45 of Fig. III becomes ineffective. The pencil guide 39 of Fig. X at its lower end is drilled to freely pass the lead 44. VIts upper tical or y-aXis of the ellipse.

end is bored out to provide a sliding fit for the sleeve 71, which is slipped over the lead 44. This sleeve also can slide in the bore of the nut 72, which may be screwed onto the thread 73, cut on the pencil guide 39 and be used toregulate the force of the spring 74 trapped between the nut and the sleeve 71. The pencil guide may `again be slipped into the bushing 33 pressed into the square 2l and locked thereto by means of the screw 43. Thus the reaction of the =light spring 74 is transferred to the square and via the flange 5S to the disc 8 and the spindle 7. The latter is mounted on the pivot pin 4, which has a Washer 40 and gripring 41 on both sides. A light axial pressure on the knob 13, exercised while rotating it, will suffice to take up this reaction.

This ellipsograph is operated in a similar manner as those described before, except for the adjustment of the cccentricties of its discs, which is as follows:

First the knob is turned until the pointer 75, pressed in the square, is on the centerline of the scale 17a on the base pflate. In this position the slots 14 in the discs will be vertical and also the scriber will be on the Y -axis of the ellipse. In this position the knob is pushed down with a force suicient to overcome the load of both springs inside the knob and the nuts 63 are tightened. After releasing the pressure on the knob both discs will be free. The square is now moved so that the pointer travels along the scale ''a until the desired vertical eccentricity is indicated at the pointer. In this Vposition again the knob is pushed down. This clamps the discs and permits loosening the nuts 63 completely. When releasing the pressure the discs remain clamped.

Now the knob is turned until the pointer is on the centerline 17 of the horizontal scale on the base plate.

he slots i4 will now be horizontal and the scriber is on the X-axis of the ellipse. The knob is now depressed with a lesser force, sufficient to compress spring 65 only. After the nuts are tightened and the pressure released only disc lt) will be free and the pointer is moved along 17 until the desired horizontal eccentricity is read on the scale. One more application of pressure on the knob and release of the nuts 63 completes the setting.

Having described three constructions incorporating the invention it will now be demonstrated that these devices produce ellipses that `are mathematically correct. For this purpose reference is made to Fig. VIII in which OX and OY are perpendicular axes through the origin O and OA and OB are vectors passing through O and making an angle of a9 with the Y-axis. Let OA=R be equal to the eccentricity of disc 1i) and OB=r to that of disc 3. Then when changing the angle a, the vector and points will describe concentric circular paths cor responding to the paths of the centers of the circular discs, when these are rotated. Thus the center O corresponds to the center of pin 4 and the angle of a9 to the angle of rotation of the disc assembly, measured from the position shown in Figs. l and V. In this position 610:0, x=0 and y=OB=r. After rotating the disc assembly a it will be noted from Fig. VIII that x=OD=R sin a (l) y=0E=r cos a (2) but x is equal to the horizontal travel of the square measured from the point where x -0. It therefore corresponds to the distance of the scriber point to the ver Further (r-y) is equal to the vertical travel of the square, downward from the point where y=r. Therefore y is equal to the distance of the scriber point to the horizontal axis of the ellipse. Thus x and y are the coordinates of the scriber referred to the axes of the ellipse to be drawn. But the Equations l and 2 may be transposed as follows:

Y ellipseV with'reference to stationary guides.

Y 7 Y which upon addition produce:V

ath-2 with half'axes R .and r, referred to its principal axes.

In one of the Equation 3 or 4 the value of a may be changed to aLl-186, leaving the other equal to ai. This has Vno inuence on Equation '5, which means that the same ellipse will be produced whether discs 8 and it? are adjusted on the spindle 7, with the two eccentricities in the same. or in the opposite direction.Y

We are .aware that the following U. S. patents: 2,468,320, dated April 26, 1949; 2,595,417, dated May V6, 1952; 2,762,126 dated September 1l, 1956; make use corresponding,toy the well known equation of an ellipse,

of the Ysame mathematical theory outlined above and Y that all use two Vstacked discs that are rotated. All,

however, have the scriber mounted on the discs, so that consequently eachV point of each disc must describe the This means that the operator must perform a complicated movement against a variable resistance. He furthermore sirnultaneously, with the same hand, must adjust 'the scriber pressure and in the first mentioned patent he must, moreover, with the other hand control the guide means. In all cases there are also frictional forces induced, that make the operation moreV diiiicult and theV outcome more uncertain, In our invention all these dithculties are avoided. The friction has been reduced to a minimum and the operator must only turn a knob `about its xed center againstV a lconstant resistance.

Therefore we believe to have contributed to the development of a simple, more easily manipulated ellipsograph.

Furthermore if R;r, Equation 5 becomes that of a ciraxis, a structure having two flat surfaces perpendicular Yto'each other and to said planes, means for maintaining contact between-one oifsaid surfaces and the periphery of one of said discs and of the other surface Ywith the periphery of the other disc, means for constraining the motion of said structure to translation parallel to said planes, a scriber mounted on said structure and Vmeans for rotating said spindle.

Y 2. An ,ellipsograph comprising a spindle mounted for rotation about its axis, a pair of circular discs stacked on said spindle in planes perpendicular to said axis, a ,radial lslot inY said' discs for adjustably mounting Vsaid discs eccentricallyY on the spindle, a structure having two at surtacesrperpendicular Vto each other and to said planes, means for maintaining contact between one of said surfaces and the periphery of one of said discs and of the other surface with the periphery of the other disc, means for constraining Vthe motion of said structure to translation parallel to saidrplanes, fa scriber mounted -on said structure and means for rotating said spindle.

. 3. An ellipsograph comprising a base plate, a spindle mounted thereon for rotation about its axis, a pair of circular discs stacked' on said spindle in planes perpendicular to said axis, a radial slot in said discs for adjustablygmounting said discs eccentrically on the spin-V dle, a structure having two flat surfaces perpendicular to each other and to said planes, means for maintaining contact between one of lsaidpsurfaces and the periphery of one of said discs and of the other surface with the for rotating said spindle.

,4. An ellipsograph comprising a base plate,` Va spindle mounted thereon for rotation about itsl axis,l apair of circular discsstacked on said spindle in planes perpendicular to said axis, a radial slot in said discs Vforpadjustably mounting said discs eccentrically on the spindle, a structure having a substantially square internal opening, the opposite sides of said openings Vbeing in the same plane, adjacent sides ybeing in diterent planes, each pair of parallel sides being in contact with one of said discs, means for constraining the motion of said structure to translation parallel` to said planes, ya scriberV mounted on said structure and means for rotating said spindle. f

5. An ellipsog'raph comprising a base plate, a spindle mounted thereon for rotation'about its axis, a pair of circular discs stacked'on said kspindle in planes perpendicular to said axis, a radial slot in said discs for adjustably mounting said discs eccentrically on the spindle, a structure having a substantially square internal opening, the opposite sides of said opening beingV in the same plane, adjacent sides being in different planes, .each pair of parallel sides being in contact with one of said discs,

y aV oating knee piece, connected vto said base plate by means of a pair of identical and parallel links and to said structure by means of another pair of identical and parallel links, a scriber mounted on said structure, a knob for clamping said discs to the spindleV and revolving said spinle about said pivot pin. f

6. An ellipsograph comprising a base plate, a pivot pin ixed to said base plate, arspindle mounted on said pivot pin so as to permit rotation of said spindle about its axis, a pair of circular discs stacked yon said spindle in planes perpendicular Yto said axis, a radial slot in said discs for adjustably mounting said discsieccentrically on the spin- Vdle, a structure having'a substantially square Vinternal opening, the oppositeY sides of said opening being in the samen plane, adjacent sides-being in different planes, each pair of parallel sides being inV contact with one of said discs, a floating knee piece, connected to said base plate by means of'a pair of identical and parallel links and to said structure by means of another pair of identical and parallel links, a scriber mounted on said structure, a'knob for clamping said discs to the spindle and revolving said spindle about said pivot pin. Y Y

7. An ellipsograph comprising a base plate, a pivot pin fixed to said base plate, a spindle mounted on said pivot pin so as to permit rotation of said'spindle about its axis, a pair of circular discs stacked on said spindle in planes perpendicular to said axis, a radial slot in each disc permitting eccentric positioning of said discs on said spindle, means for aligning the center of said discs in a plane through the axis of said spindle, a structure having a Substantially square internal opening, the opposite sides ofV said opening being in the same plane, adjacent sides being i in different planes, each pair of parallel sides Ybeing in Y contact `with oneY Vof said discs, a floating knee piece,

`connected to said base plate'by means of a pair of identical and parallel links and to said structure by means of another pair of identical and parallel links, a scriber mounted on said structure, a knob for clamping saidY discs to the spindle and revolving said spindle about said pivot 8. An ellipsogr'aph comprising a base plate, a pivot pin i fixed to said base plate, a spindle mounted on said pivot periphery of the other'disqgmeans for constraining ther-v.

motion of said structure't translation parallel to said c7.5

pin so as to permit rotation of said spindle about its axis, a pair of circular discs'stacked on said spindle in planes perpendicular to `said axis, a radial slot in eachpdisc permit-ting eccentric positioning of said discs on said spindle, Y vmeans .for aligning the centers of said discs in a plane 'through the axis of said spindle, a structure having a sub1 stantially'square, internalopening, the opposite sides of *said opening being in the same plane, adjacent sides being in dilerent planes,jeach pairVr of parallel sides beingrin contact with one of said discs, =a oating knee piece, connected to said base plate by means of a pair of identical and parallel links and to said structure by means of another pair of identical and parallel links, a scriber mounted on said structure, a knob having internal resilient means for selectively clamping said discs -to the spindle and revolving said spindle about said pivot pin.

9. An ellipsograph attachment for drafting machines comprising a base plate positioned on the drawingboard upon which the drafting machine operates, a pivot pin fixed to said base plate, the axis of said pivot pin being perpendicular to the drawingboard, a spindle rotatably mounted on said pivot pin, a pair of circular discs stacked on said spindle in planes perpendicular to said axis, a radial slot in said discs for adjustably mounting said discs eccentrically on the spindle, a structure having two flat surfaces perpendicular to each other and to said planes, means for maintaining contact between one of said surfaces and the periphery of one of said discs and of the other surface with the periphery of the other disc, means for fastening said structure to the scale bracket of the drafting machine, a scriber mounted on said structure and means for rotating said spindle.

10. An ellipsograph attachment for drafting machines comprising a base plate positioned on the drawingboard upon which the drafting machine operates, a pivot pin fixed to said base plate, the axis of said pivot pin being perpendicular to the drawingboard, a spindle rotatably mounted on said pivot pin, a pair of circular discs stacked on said spindle in planes perpendicular to said axis, a radial slot in said discs for adjustably mounting said discs 'eccentrically on the spindle, a structure having a substantially square internal opening, the opposite sides of said opening being in the same plane, adjacent sides being in different planes, each pair of parallel sides being in contact with one of said discs, means for fastening said structure to the scale bracket of the drafting machine, a scriber mounted on said structure, a knob for clamping said discs to the spindle and revolving said spindle about said pivot pm.

11. An ellipsograph attachment for drafting machines comprising a base plate positioned on the drawingboard upon which the drafting machine operates, a pivot pin fixed -to said base plate, the axis of said pivot pin being perpendicular to the drawingboard, a spindle rotatably mounted on said pivot pin, a pair of circular discs stacked on said spindle in planes perpendicular to said axis, a radial slot in said discs for adjustably mounting said discs eccentrically on the spindle, a structure having a substantially square internal opening, the opposite sides of said opening being in the same plane, adjacent sides being in different planes, each pair of parallel sides being in contact with one of said discs, means for fastening said structure tothe scale bracket of the drafting machine, a scriber mounted on said structure, a knob having internal resilient means for selectively clamping said discs to the spindle and revolving said spindle about said pivot pin.

No references cited.

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