US2961769A - Planetary ellipsograph - Google Patents

Description

NOV- 29 1,960 c. E. MowRY PLANETARY ELI..IPSOGRAPH Filed Sept. 13, 1954 l 4 Sheets-Sheet 1 N N N) N JNVENToR.

Nov. 29, 1960v c. E. MowRY 2,961,769

PLANETARY ELLIPSOGRAPH Filed sept. 13, 1954 4 sheets-sheet 2 IN VEN TOR.

615 Wawy United States Patent f) PLANETARY ELLIPSOGRAPH `Charles E. Mowry, Santa Clara County, Calif. (103 Cleveland Ave., San Jose 28, Calif.)

Filed Sept. 13, 1954, Ser. No. 455,684

4y Claims. (Cl. 33-30) This invention relates to improvements in mechanical drafting instruments, or delineating devices of a type commonly known as planetary ellipsographs for drawing, tracing, or delineating partial or complete ellipses of infinitely variable eccentricities by means of one suitably Iadjustable instrument; and still more particularly to devices delineating a complete ellipse at one setting and positioning of the instrument.

It has been the general practice heretofore to delineate or draw ellipses by plotting a finite number of points at locations determined by arithmetical or graphical computations, and then by drawing approximate curved lines, or aggregations of fragmentary circular arcs through the plotted points; or by tracing approximate ellipses from fixed elliptical templates; or by using a trammel type ellipsograph. All such previously used methods are time consuming, relatively inexact, or require the use of cumbersome and expensive apparatus that is capable of delineating only a portion of an ellipse at one positioning.

It is an important object of this invention, therefore', to provide a mechanical drafting or delineating device that is capable of drawing o-r delineating a complete and mathematically and geometrically exact ellipse of any eccentricity whatsoever, yand of any size whatsoever within the maximum range of a given device.

It is also an object of this invention to provide a device that can be set or adjusted to delineate any ellipse whatsoever within its dimensional range by simple graphical drafting methods without resorting to mathematical cornputations or precision scales.

It is another object of this invention to provide a device that is capable of delineating a complete ellipse without changing or shifting the position or location of the device.

Further objects are to provide a device that can delineate ellipses quickly, simply, and economically; also such further objects, advantages, and capabilities as will fully appear yand as are inherently possessed by the device and the invention described herein.

The invention further resides in the combination, construction, and arrangement of parts illustrated in the accompanying drawings, and while there are shown preferred embodiments thereof, it is to be understood that the same are merely illustrations of the invention and that the mechanism is capable of modification and change, and the invention comprehends other details of construction without departing from the essence thereof, orv the scope of the appended claims.v

Referring to the drawings:

Figure 1 is a sectional elevation of a first embodiment of my invention taken on a central. plane.

Figure 2 is a fragmentary end elevation viewed as indicated bythe arrows lI-II of Figure l.

Figure 3 is a fragmentary transverse section viewed on a plane as indicated by the arrows III-III of Figure 1.

Figure. 4 -is a fragmentary end elevation viewedas indicated4 by the arrows IV-IV of Figure 1.

A 2,961,769 Patented Nov, 29 19.60

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Figure 5 is a plan view of the device as shown in Figure 1.

Figure 6 is a fragmentary sectional elevation taken on a central plane ofV apreferred form of stylus holding means which is not. sectioned when it appears in other figures due to the small scale.

Figure 7 is a fragmentary sectional elevation of a position holding device viewed on a plane indicated by the arrows VII-VII of Figure 5. Y

Figure 8 is a plan view of a second embodiment of my invention. Y C

Figure 9 is a sectional elevation takensonl a central plane as indicated by the arrows IX-IX of Figure 8.

Figure l0 is a fragmentary end elevation viewed as ndicated by the arrows X-X of Figure 9.

Figure ll is an end elevatiorrviewedas indicated by the arrows XI-Xl of Figure 9. Y Y

Figure l2 is a fragmentary sectional elevation taken on a plane passing through the axes of an alternative construction of the iiexible shaft mechanism of Figure 9'.

Figure 13V is a fragmentary plan section of the speed changing mechanism viewed` as indicated by thek arrows XIII-XLII of Figure 9.

Figure 14 is an alternative construction ofthe mecha--V nism shown in Figure 13.

Mechanism to accomplish this scheme of operation is shown in the gures of the drawings, in which like reference numerals indicate like mechanical parts inthe several views.

Referring to Figures 1 and 5, the two straight edges 1 and la placed externally to the workingk area provide a base and partial positioning means for the device. How ever, one such straight edge could be made to sufliceby using a counterweight in an obvious manner to maintain the instrument in a vertical position.

The straight edges l and 1a are preferablyv made of transparent plastic material which has a coefficient of friction with paper of something between .2 and .35, depending upon the amount of dust present. The co..- eicient of friction may be increased to something between .5 and .6 without the use of needle points by means of the button 2 shown in Figure 7. Therein is seen a sleeve 3, pressed or otherwise fixed in the straight edge 1. A cap 4 is adjustably positioned on the top of the sleeve by fairly tight threads as indicated by dotted lines. Threaded' through the top of the cap is a screw 5 which has a needle point 6 formed on its bottom end. A capsule 7, bored to permit passage of the smooth lower end of the screw, is slidably mounted in the sleeve with. a suitable shoulder arrangement to prevent its complete extrusion. A soft rubber plug 8, also bored to permit passage of the screw, is held in the lower end of the capsule to provide high friction contact with vsupporting surface 9 during the shifting of the instrument in.- cident to positioning when the Vneedle pointA Will be retracted. It will be noted that the lower surface of plug 8 is shown hemispherical in shape having substantially sharp edges adjacent to the screw shaft. This ap, parently permits the rubber to press aside any dust present an-d penetrate among the fibers of the paper in a manner to increase the coefficient of friction materially. In order to obtain substantially equal pressures from the several buttons when the instrument is resting on a. slightly uneven surface, the capsule 7 is pressedV downward by a spring 10 which may be suitably compressed by adjusting the threaded cap. After the instrument has been shifted into operating position, the screw 5 may be run down to engage the needle point and hold the instrument insposition. On steeply sloping surfaces, the, instrument may also be further held in position by pieces of adher-r obvious manner.

` Referring again to Figures 1 and 5, a base, or support for the operating components is provided by an overhead frame 11 which is mounted on the straight edges 1 and 1a and is held and positioned thereon by means of countersunk screws 12 and dowel pins 13. For reasons that will appear later, there is no particular need to have this mounting adjustable. The frame has arms 14 extending at substantially 45 angles to the major axis of the instrument. Some such angle is preferred for two reasons: first, it permits greater visibility of and access .to the working parts and area; and, second, it gives maximum clearance for the rotating secondary arm when delineating ellipses of maximum dimension and eccentricity.

. It will be further noted that the frame in Figures 1 and is shown as an integral structure. This is preferable in the larger size oliice, or loft type instruments Where extreme accuracy is desired and portability is a secondary consideration. It is obvious that this frame could be jointed or articulated after the manner shown in Figure 11, if it were so desired.

A bored boss 15 is formed in the top center of the frame to provide a sliding seat for hub 16 of a first, or sun, gear such as bevel gear 17. The gear 17 is mounted to be irrotatable about its own axis by a key 18 xed in the boss and engaging a straight keyway 19 in the hub.

The hub 16 is bored to provide a bearing for a journal 22, which is further held in alignment by conical thrust collars 23 and 24. Collar 24 is fixed on the journal. At this point, attention is called to the fact that while plain bearings, journals, and thrust surfaces are shown throughout this specification for ease of illustration, it is contemplated that in the more expensive instruments of maximum accuracy pre-loaded anti-friction type bearings may be employed in a manner well known to those skilled in the art.

As indicated in Figure 1, the geometric axis of the journal 22, extended to the working surface 9, corresponds to the origin of an ellipse. This geometric axis is referred to in the claims as the central vertical axis.

A manual operating knob 25 formed integrally with collar 23 is fixed on the upper end of journal 22 by means of screw 26 and key 27.

When not pressed down by the operator to obtain stylus contact, a spring 29 interposed between the frame 11 and knob 25 holds the operating mechanism in the raised position shown for reasons to be amplified later.

The primary rotating arm is provided through the medium of square rails 32. These rails are irrotatably fixed to the journal 22 through the medium of a bracket 33 depending from the collar 24, and held to the rails 32 by clamp 34.

A second bracket 36 is xed to the rails 32 by clamp 37. Additional stiffness is provided by stub rails 42 and clamps 43 and 44.

A bearing is bored in the bracket 36 to receive a journal 47 formed on an extended hub of a second bevel gear 49, which is positioned axially by shoulders and split ring 52, and is in operational engagement with gear 17. Graphical drawing symbols are used for these and other gears and sprockets because of the small scale of the drawings.

A square driving shaft 53 is fixed concentrcally in second gear 49 and extends in a plane passing through the extended axis of the journal 22.

To provide support for the planetary pivot, a car- -riage 54 is slidably mounted on the rails 32, and is xed in position as desired by clamp 55, and screw and knob 56. A removable bracket S8 is held on carriage 54 by screws 59 and is bored to provide a bearing for journal 60 formed on an extended hub of a third bevel gear 61, which is positioned axially by shoulders and a split ring 62. The bracket 58 is made removable to permit assembly.

As can best be seen in Figure 3, a second bracket formed on carriage 54 is bored to provide a bearing for journal 63 formed on an extended hub of fourth, or planet, bevel gear 64 which is in operational engagement with bevel gear 61.

The over-all speed or angular reduction in the gear train between gears 64, 61, 49, and 17 must be two to one if the instrument is to draw an ellipse.

By having the shaft 53 pass through the extended axis of journal 22, and by having the second and third, or intermediate driving, gears spatially disposed outside the space between the axes of the sun and planet gears, the latter automatically rotates the secondary arm in the opposite spatial sense relative to the rotation of the primary arm and shaft 53. It also leaves the space under the rst bevel gear clear so that the axis of the planetary gear may be moved under it for drawing the smaller ellipses.

Referring again to Figure 3, the-secondary rotating arm is provided thro-ugh the medium of square rails 66, These rails are adjustably fixed to the journal 63 by a bracket 67 and clamp 68. The adjustable feature is provided by screw 72 and set screw 73- of Figure l.

The need for, and nature of, all adjustable features will be discussed later under one heading.

A carriage 74 is slidably mounted on the rails 66, and is xed in position as desired by a clamp 75, and screw and knob 76. A projection 77 of bracket 74 provides support for lead or stylus holding means 80. As shown in Figure 6, the stylus holding means comprises a sleeve 81 tixed in projection 77; a thimble 82 is held on sleeve 81 by threads 83 and aligning surfaces 84; a split conical ended collet 85 is compressed between suitable recesses in the lower end of sleeve 81 and thimble 82; a lead, stylus, or pen 86 is then firmly and concentrically xed by the collet 85.

In order to delineate an ellipse of exact size it is necessary that the pivot of the planet gear and tracing point be precisely positioned on their respective rotating arms. This may be accomplished by adding any one of several well known mechanisms such as those used on beam compasses, vernier calipers, and the like. Such mechanism is omitted here to simplify the drawings.

To prevent the outer end of driving shaft 53 from being bent in handling, a bracket 104 is held on rails 32 by clamp 105. A journal turned on the end of the shaft operates in a supporting bearing 108 of the bracket.

To facilitate factory or corrective adjustment of the instrument, and operational setting of the instrument to delineate an ellipse of given size and eccentricity, setting means are provided whereby the operator is able to project the axis of journal 22, and the axis of pivot 63, down to the operating surface 9. This isaccomplished as can best be seen in Figures 4 and 5 by an abutter screw 112'adjustably threaded through bracket 74 in such a position that it will abut against the side of bracket 67 to positively align the axis of the stylus with the axis of the planet gear. During the adjustment operation, this can be tested by temporarily disengaging gear 61 so that journal 63 may rotate freely. When the axes coincide, the point 89 of the stylus will remain at a point. A second abutter screw 114 is adjustably threaded through bracket 54 in such a position that it will abut against the side of bracket 33 to positively align the axis of the planet gear with the axis of the sun gear. During the adjustment operation, this can be tested by placing the stylus axis under the planetary axis and moving both under the axis of the sun gear and then rotating journal 22. When the axes coincide, the point 89' of the stylus will remain at a point. Before completing this explanation of adjustment and setting, one other matter remains to be discussed.

As best seen in Figures l and 5, a bracket 116 is held on frame 11 by screws 117 which pass through elongated holes in the bracket to permit adjustment. A shaft 118 passes through abearing boss on the bracket and has an perating knob 119'txed on one endand alatch 121 on theV other. The latch may be turned in to engage a slot 122 cut in the side of operating knob 25 to hold the latter stationary when adjusting the instrument, or when setting for a desired size. When the adjustment or setting is complete, the latch is turned out of the slot and the operating knob is free to turn.

And now the manner in which the various adjustable components cooperate to permit purely graphical positioning, adjusting and setting the instrument can be fully discussed. First, there are the adjustable stops which permit the axes of the stylus, the planetary gear, and the sun gear to be brought into accurate alignment; second, there is` the straight edge which permits the directional alignment of the instrument with the work surface; third, there is the restraining latch against which the gears can be turned to take up the backlash; and fourth, there 'is the means for the angular tixed positioning of all moving elements to bring the stylus to its correct and necessary starting position on the major axis. lf lines have been drawn along the minor axis extended, where transverse index lines 126 and 126a inscribed on the straight edges 1 and 1a in a plane passing through the central axis of the instrument can be brought into coincidence, the instrument will be properly oriented. This can be tested by bringing the stylus axis and the planetary axis under the center axis of journal 22 and seeing that the point of the stylus coincides with the desired center of the ellipse. lf it does not, corrected reference points may be scratched near lines 126 and 126a if the straight edges are rigidly attached to the frame, or the position of the straight edges could be changed if they are adjustably mounted. Next, to check the backlash adjustment of thev instrument, slide the planetary axis with stylus still under it to the farthest extent of Vits outward travel. Then with latch 121 engaging slot 122, press against the primary arm in a direction opposite to the desired rotation with suflicient force to take up the backlash and see if the stylus point remains on the major axis.. If it does not, loosen screws 117 and adjust bracket 116 until the stylus point is on the line, while the backlash is taken up, then tighten screws 117. Next, to take up the backlash between gears 61 and 64, move the stylus to the farthest extent of its outward travel, then press against the secondary arm in a direction opposite to the desired travel, with sufficient force to take up the backlash and see if the stylus point remains on the line. If it does not, loosen screw 72 and set screw 73- and rotate the secondary arm on its journal until the stylus point is on the line, while the backlash is taken up, and then tighten the screws.

These fully adjustable features are of considerable practical importance because they permit the instruments to be manufactured with only ordinary commercial precision in machining as opposed to the ultra precision required if they were not fully adjustable. Thisrenders them lessexpensive in the first place and insures continued accuracy even after years of use and Wear.

Next will be explained how the instrument is set, and an ellipse drawn, As previously explained, the center of' the ellipse, a point midway between the length ofthe major and minor axes lying on the major axis, and the endof the major axis will have been located on the working surface by the draftsrnan. The planetary axis and stylus axes of the instrument will be brought under the central axis of the instrument and the latch 121 en gaged. The instrument will then be oriented as previously described and positioned so that the stylus point is over the center of the ellipse on the workingl surface. Then the planetary axis and stylus axis are moved outward until the stylus point is over a point on the major axis of a length midway between the major and minor axes, and carriage 54 clamped in place. Next the stylus point is moved outward until it is over the end of the major axis, and carriage 74 clamped in place, and the latch 121 6 disengaged. The operator then presses down on the frame with one hand or lowers needle points 6 to hold the instrument in position, and rotates the knob 25 with his other hand in the direction chosen when the backlash was taken up, say in a counterclockwise direction, pressing down as he does so to obtain the desired stylus contact. When using pen and ink, the pen will thus be raised by the spring whenever the downward pressure is released.

Thus a complete ellipse is delineated at one setting of the instrument. It `should also be obvious that, since there is no limitation on the positions that the planetary axis .and the stylus axis can assume on their respective arms, there is no limitation whatsoever upon the eccentricity of the ellipses that can be drawn. Neither is there any limitation whatsoever upon the sizes of the ellipses that can be drawn within the limits of a given instrument.

It should also be clear that, after having been started in one direction, the stylus will not retrace a path perfectly in the reverse direction; if reversed, it will followV the path of an ellipse having its axes rotated by an amount proportional tothe backlash in the gears. Such deviation may not be much, perhaps only once or twice the width of a pencil line, but even that is too much for good draftsmanship. Nor is this a particularly unfavorable occurrence, for even a simple circular compass will not, in general, retrace a path pelfectly in a reverse direction.

As previously stated, this rst embodiment of my invention is better suited for oice, or loft type instruments. There is great need, however, for a small, more portable instrument particularly adapted for delineating smaller ellipses, under six inch maximum dimension, say. A second embodiment of my invention provides such an instrument as shown in Figures 8 to 14 inclusive, and as will now be described. Attention is particularly directed to the compact and novel method of constraining the secondary arm to rotate in the prescribed manner.

The theory of oper-ation of this second embodiment is the well known one pertaining to planetary ellipsographs'.

Referring now to Figures 8, 9, and 1l, the straight edges 1 and 1a, the pressure buttons 2, and the stylus holding means Si), are covered by the same description and discussion given for the same numbered parts of the iirst embodiment, so that discussion need not be repeated here.

The overhead supporting frame is shown jointed or. articulated in this embodiment so that it may be taken apart for greater convenience in transportation and Stor age. The vertical legs comprise the struts 131 held together by the base couplers 132, and capital couplers 133 which are clamped on by screws 134. Two struts for each leg are preferred for the larger instruments for greater rigidity, but one strut for each leg will suice for the smaller instruments.

Bottom projecting ends of the struts are held in base brackets 135 fixed on the straight edges 1 and 1a by suitable screws 136 and dowel pins 137; the ends are locked in position by clamps 133, and screws and knobs 139. Top projecting ends of the struts are held in capital brackets 142, which are formed in top plate 143, by clamps `144, and screws and knobs 14S. Linear alignment is assured by the V grooves engaging the square struts, and correct lengths by the abutting surfaces between the couplers and brackets. Minor corrective adjust ment of the lengths of the legs can be'obtained by resetting the couplers in an obvious manner.

A bored boss 146 is formed in the top center of the top plate 143 to provide a sliding seat for a bushing 147 which is restrained from rotation by a key 148 xed in the boss 1.46 and engaging a straight keyway 149 in the bushing.

The bushing is' bored to receive an extension 153 of a journal 154 the axis of which is referred to in the claims as the central vertical axis. The journal is reduced in section to provide ,a` shoulder to abut washer 155. Bear ing bracket.156 encircles theextension 153 at the top, of

7 the bushing and the assemblage is held tightly together by threaded nut 157.

A supporting collar 158 is formed integrally on the bottom end of journal 154 to support bearing 159 which is rotatably mounted on the journal. The exterior of bearing 159 is of rectangular form. A toothed gear 162 is fixed on Vthe top of bearing 159 and the integral structure thus formed is rotatable on the journal but restrained axially between collar 158 and washer 155.

The gear 162 may be rotated by the operator through the medium of pinion 163 which is fixed on a shaft 164 extending upward through bearing holes in plate 143 and bracket 156. A manual operating knob 166 is fixed onto the upper end of shaft 164. By pressing down on this operating knob as he rotates it, the operator may hold the stylus in contact with the working surface with manually controllable force. A depending strut 167, which may well be a U-shaped Stamping as shown, slopes downward from bearing 159 to which it is fixed by any suitable method. A bracket 172 is fixed to the lower end of strut 167. Primary arm guide rails 175 are held in V grooves in bracket 172 by clamp 176.

A carriage 178 is slidably mounted on the guide rails 175, and may be fixed in adjusted position by clamp 179, and screw and knob 182, mounted in a yoke extending up from the carriage. A gear, or sprocket, housing is formed in the bottom portion of the carriage and is closed by a cover plate 183 held in place by screws 184 and dowel pins 185 as indicated in Figure 13.

As shown in Figures 9, 13, and 14, bearings are bored in carriage 178 and cover plate 183 to receive shaft 186 on which sun gear or sprocket 187 is fixed; shaft 188 on which planet gear or sprocket 189 is fixed; and, if gears are used, shaft -190 on which idler gear 191 is fixed. Such an idler gear is necessary in order to obtain the correct direction of rotation for shaft 188. In Figure 13 the sprockets are shown interconnected by toothed belt 192. A miniature chain may be employed in place of the belt in an obvious manner. It also may prove necessary to add a belt or chain tightener in the well known manner if later experience shows that these miniature components Wear too rapidly.

The gears or sprockets are restrained axially by suitable contiguous bosses on the carriage and cover plate in the usual manner.

The operation of sun gear 187 is novel in that it is mounted to be irrotatable about its own axis, although its axis travels in a concentric circular path about the axis of journal 154 extended. This effect is obtained through the medium of a flexible shaft interconnecting the top end of shaft 186 and the bottom end of journal 154. As shown in Figures 9 and l1, this flexible shaft comprises a bored boss 194 formed on the underside of collar 158 to receive a bushing 195 which is fixed in place by a set screw 196. A suitable length of flexible cable 197, such as that used for automobile speedometers and the like, has one end fixed in the bushing 195. The other end of the fiexible cable is fixed in a second bushing 198 that is slidably engaged in a recess formed in the upper end of shaft 186. The bushing 198 is restrained against rotation by pins 199 fixed in the shaft and engaging suitable keyways in the bushing. It has been demonstrated in the literature pertaining to advanced mechanics that such a exible cable, or wire, is equivalent to a large number of universal joints interconnected with intermediate shafts so disposed as to transmit angular displacement without relative angular displacement between the ends of the fiexible cable, or wire. Accordingly, gear or sprocket 187 will not rotate about its own axis as it travels about the axis of journal 154.

For practical purposes the waviness, or deviation, made in an ellipse if gear 187 does oscillate a small amount about its own axis can be detected only by measurements of the highest precision. Since this specification proclaims a device that will delineate mathematical and geometrically exact ellipses, however, it is deemed necessary to include this explanation.

The fiexible shaft as above described and as shown in Figures 9 and ll is preferred for the smaller sizes of in- Struments. But for the larger sizes, an alternate construction of the flexible shaft may be preferred, as shown in Figure l2. Therein can be seen a sleeve 202 fixed on shaft 186 and providing a fork in which are bearings for pin 2013 of a universal joint. A cross pin 204 and spacer 205 provide constrained attachment for a cross fork formed in the end of shaft 206. Shaft 286 fits slidably inside a tube 207 and is irrotatably attached thereto through the medium of drive pin 208 fixed in the shaft and engaging slots in the tube. The upper end of tube 207 is connected to the lower end of journal 154 through the medium of a second universal joint comprising a fork on the end of the tube, spacer 209, cross pins 211 and 212, and fork 213, formed integrally with collar 158 of the journal.

It is shown in standard textbooks on advanced mechanics that two shafts driven through the medium of two universal joints and an intermediate shaft will not have relative angular displacement during a revolution when the two fork pins of the `intermediate shaft pass simultaneously through planes passed respectively through the axes of the driver and intermediate shafts, and the axes of the driven and intermediate shafts. In this case, the axes of driver, intermediate, and driven shafts always remain in the same plane during the course of a revolu tion. Therefore, the intermediate shaft fork pins should be parallel, which they are.

It is obvious then that the construction of Figure 12 will perform the functions previously described for the construction of Figures 9 and 11.

Shaft 188 provides the support and dniving meansrfor the secondary arm which comprises a guide rail 227 fixed in bracket 228 which is adjustably held on shaft 188 by suitable set screws 231, as shown in Figure 10.

`Carriage 232 is slidably mounted on rail 227 and may `be held in adjusted position by clamp 233 and screw and knob 234'. Suitable stylus holding means such as 80 previously described are fixed in a projection 235 of carriage 232.

Fine adjustment of carriage 178 is provided by a lead screw 236 threaded through the carriage and rotatably supported in clamp 176. The lead screw may be rotated by knurled wheel 237 fixed thereon. Similarly, carriage 232 may be finely adjusted by a lead screw 239 rotatably mounted in the carriage and threaded into a clip 240 fixed on bracket 228. This lead screw may be rotated by knurled wheel 241 fixed thereon and constrained axially by clip 242 fixed on the carriage.

Positive alignment of the pivots and stylus for adjustment and setting of the `instrument is provided by suitable means such as an abutter screw 243 threaded through clamp 176; and `by abutter screw 244 threaded through carriage 232.

Backlash controlling means is provided by a latch 246 rotatably mounted on pin 247 held in bracket 248 which is fixed on strut 167. Corrective adjustment is provided by a set screw 249 threaded into a boss 250 fixed on plate 143. Operational locking is provided by screw and knob 251 lsupported by bracket 252.

The stylus may be latched out of contact with the working surface when desired by leaf spring 257 held on plate 143 by screw 258 and engaging the under surface of bracket 156.

The corrective adjustment, control of backlash, and setting of this second embodiment follows the same general procedure thoroughly explained for the first embodiment and need not be repeated here.

Future experience may show that another variation of this second embodiment is desirable, particularly for making perspective layouts of flanged piping in which numerous ellipses must be drawn and exact ellipses are highly desirable since interference between parts is a problem. Such variation would be an instrument capable of being mounted directly on the arm of a universal drafting machine. The manner of adding such a mounting lug on one or other of the straight edges is thought to be obvious and well known and is neither shown nor claimed.

A brief consideration of either the gear, sheave and belt, or chain and sprocket arrangements shown will disclose that the secondary arm will rotate in the opposite spatial sense relative to the primary arm, and, as before, the overall gear train, sheave, or sprocket ratio must be two to one.

I claim:

1. In combination with a planetary ellipsograph which comprises an overhead supporting frame having a central vertical axis, a sun gear mounted to be irrotatable about its own axis and supported by the frame, a planet gear one-half the diameter of the sun gear and means causing the planet gear to rotate about its own axis in a sense opposite to the travel of the planet gear about the sun gear, a primary arm mounted for rotation about the central vertical axis and supporting the planet gear, a depending scriber arm xed for rotation with the planet gear, an adjustably mounted stylus on the scriber arm, setting means whereby the axis of the planet gear may be irrotatably moved to align positively with the central vertical axis, means whereby the axis of the stylus may be irrotatably moved to align positively with the axis of the planet gear; backlash controlling means comprising latching means for locking all rotatable pans against rotation, said latching means being adjustable to a iixed position.

2. The device of claim 1 wherein the sun gear is slidably mounted on the primary arm and is restrained against rotation about its own axis by a exible shaft connecting said sun gear with said supporting frame.

3. The device of claim 2 in which there is also a straight edge external to the working area over which the frame is to be fixed, a transverse line on the straight edge located in a plane through the central axis of the instrument, adjustably spring pres-sed high friction means on the straight edge, and retractable needle points mounted within the high friction means.

4. The device of claim 1, in which there is also a straight edge external to the working area over which the frame is to be xed, a transverse 1in-e on the straight edge located in a plane through the central axis of the instrument, adjustably spring pressed high friction means on the straight edge, and retractable needle points mounted within the high friction means.

References Cited in the file of this patent UNITED STATES PATENTS 333,972 Rummell Jan. 5, 1886 623,227 Veronese et al Apr. 18, 1899 957,114 Shea May 3, 1910 1,264,157 Clarke Apr. 30, 1918 1,623,348 Kiefer Apr. 5, 1927 2,504,832 Groome Apr. 18, 1950 FOREIGN PATENTS 4,582 Great Britain A.D. 1885 15,134 Great Britain A.D. 1896 258,492 Germany Apr. 8, 1913 247,733 Switzerland Dec. 16, 1947 469,520 Italy Mar. 4, 1952 281,463 Switzerland June 16, 1952

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