US2324041A - Geometrical instrument - Google Patents

Description

July 13, 1943. SUVERKROP 2,324,041

GEOMETRICAL INSTRUMENT Filed 'June 14, 1940 3 Sheets-Sheet -l July 1 3, 1943. Y L, SUVERKROP 2,324,041

GEOMETRI INSTRUMENT Filed Jzrw 14, 1940 3 Sheets-Sheet 2 VIII Juiy 13, 1943. L SUVERKRQP 2,324,041

GEOMETRI CAL INSTRUMENT Filed June 14, 1940 3 Sheets-Sheet 3 Patented July 13, 1943 UNITED STATES PATENT OFFICE 16 Claims.

My invention relates to improvements in geometrical instruments generally, and more particularly to draftsmens compasses and measuring instruments. Its functions include the drawing of circles and the measuring or laying off of distances.

During the past few decades there has been a marked increase in the proportion of drawings finished in pencil for reproduction by blue printing, etc., without making an inked tracing. As a further step in elimination of time-consuming methods and equipment in the drafting room, the so-called drafting machines have come into more general use. In place of T-square, triangles, protractor, and scales, these machines provide a pair of scaled straight-edges at right angles to one another which may be moved anywhere over the drafting board while the drafting machine retains their parallelism with lines drawn on the drafting paper and at the same time, if desired, permits turning the straight-edges at angles. These machines e iminate many separate articles of equipment which formerly cluttered up the drafting board; and, by making the drawing of measured straight lines a direct process instead of one of trial-and-error involving T-square, triangles, protractor, and scales, have resulted in quicker and better work.

However, the drawing of circles is still gener ally done by setting a compass according to a separate scale. This procedure is entirely inconsistent with the efiicient straight-line drawing made possible by the drafting machines. The

"amount of time taken will be clear when it is considered that in order to have circles drawn with a total accuracy tolerance of inch (that is, plus or minus inch) the compasses must be adjusted to the nearest inch. The difiiculty is even more apparent in the new drafting practice where the fractional system has been dispensed with and all dimensions are expressed in inches and decimals of an inch on drawings the drafting of which is done with some effort to hold an accuracy of 0.01 inch. The matter is of importance as this practice becomes increasingly general. Still more apparent is the inconsistency where the so-called civil engineers model of drafting machine is used. With that model, angles can and are read to the nearest 1. In an effort to measure and indicate distances on the map with corresponding precision, considerable pains are taken to hold to an accuracy of at least 0.01 inch.

Some progress has been made in developing compasses that are sufficiently sturdy so that circles may be drawn in pencil opaque enough for reproduction Without inking. But so far nothing has appeared on the market in the form of a practical drafting compass offering accuracy and speed consistent with what the drafting machine offers in the drawing of straight lines. In principle the problem of drawing measured distances and circles quickly is answered by the measuring compass. The principle is not new as is well known by every school boy who has seen the flimsy measuring compass used in geometry class. But there is no measuring compass available presenting the combination of sturdiness, ease of adjustment, and accuracy required in modern drafting.

The objects of this invention, which result from an examination and analysis of the problem, may be generally stated as providing a practical draft ing compass which includes a scale and means for readily adjusting the compass points to any distance within the range of the instrument. In detail, some of the objects are as follows: (a) To provide a measuring compass the scale of which indicates, instead of radii, the diameters of circles. (b) To provide a measuring compass with a movable index whereby the instrument may be precisely calibrated to conform with the calibration of other scales used in drawing straight lines in the drawing where this compass is employed. (0) To provide a measuring compass with different scales which may be readily changed. (d) To provide a measuring compass with a lengthening bar by means of which the range of the compass may be increased without having the compass unduly bulky for drawing smaller circles. (e) To provide a measuring device or a compass in which toothed members are employed, with means for adjusting play between the teeth thereof. (1) To provide a measuring device or compass in which toothed members are employed, with a safety device by means of which stripping of toothed members is prevented by prelocking toothed actuating members against rnotion as an automatic process incidental to clamping the device at any dimension. (9) To provide compasses with means for readily adjusting the height of the drafting lead or other drawing means to correspond with that of the central pivot of the instrument. (h) To provide compasses with means to prevent rotation of the drafting lead when it is being adjusted for length in the compass leg. (i) To provide drafting compasses with an operating handle combining knobs of different diameters which affords better control of the instrument in drawing circles of large and small diameter. The foregoing and other objects of the invention will be clear from the following description and the accompanying illustrations, in which Fig. 1 is a side elevation of the new compass;

Fig. 2 is an elevation of the drawing end thereof;

Fig. 3 is an elevation of the end thereof opposite the drawing end;

Fig. 4 is a view of the top of the new compass;

Fig. 5 is a view of the bottom thereof;

Fig. 6 is a View of one of the detachable fine scales;

Fig. '7 is a view of another of the detachable fine scales;

Fig. 8 is a broken View of a lengthening bar for use with the new compass;

Fig. 9 is a broken view of a screw used for assembling the new compass with the lengthening bar;

Fig. 10 is a cross section through the housing of the new compass, taken along the line l--I in Fig. 1;

Fig. 11 is a view of the front of the housing of the new compass;

Fig. 12 is a View of the back thereof;

Fig. 13 is a perspective view of an eccentric bushing used for adjusting play in gear teeth of the new compass;

Fig. 14 is a perspective view showing a method of attaching coarse scales to the new compass;

Fig. 15 is a cross section showing the assembly of the lengthening bar used with the new compass;

Fig. 16 is an enlarged view of the bottom of the lead clamp shown in Fig. 1;

Fig. 17 is a view of the side of the lead clamp of a compass;

Fig. 18 is a cross section thereof taken along the lines 2-2 in Fig. 17

Fig. 19 is a view of a pivot;

Fig. 20 is a cross sectional view of a quickly detached fine scale for the new compass;

Fig. 21 is an end view thereof;

Fig. 22 is a view of a new form of compass lead; and

Fig. 23 is a view showing how the new lead shown in Fig. 22 is held in the clamp of the new compass so as to prevent rotation and so as to present a flat face on the side of the lead next the pivot of the compass so that the usual method of sharpening will result in the chisel point shown in Fig. 22.

I will first give a brief summary description of the new compass as here illustrated. A beam I is used for adjusting and holding the distance between the pencil lead 6 and the pivot I2. The beam I is supported by the housing 4 and may be moved by a pinion 8 meshing with the rack 3 on the beam I. A graduated coarse scale 2 is detachably fitted to the beam I and indicates roughly by its graduations the approximate distance between pivot l2 and lead 6. A graduated cylinder I4, detachably mounted on the pinion 8 so as to turn with it, serves as a fine scale to indicate precisely small increments of movement between graduations of the coarse scale 2, such as hundredths of divisions on the coarse scale 2. A rack 29 and pinion 30 provide for the quick adjustment of the extent of the lead 6 and this minimizes the loss of time due to moving the lead in the lead clamp 2425. An extension bar is provided by means of which the range of the instrument may be extended without making the compass unwieldy for the drawing of smaller circles.

In detail, beam I, which may be fitted with the detachable coarse scale 2, has a toothed rack and is held in the housing 4. It is of hollow circular section and one end receives the head 5, which carries either a compass point or a pin or, as shown, a pencil lead 6. The housing 4 is bored to receive the eccentric bushing I in which the pinion 8 in Fig. 10 is free to rotate and the teeth of which engage with those of the rack 3. Diagonal teeth on the rack 3 engaging with helical teeth on the pinion 8 are preferable. The eccentric bushing I may be constructed to furnish a bearing on only one side of the toothed part of the pinion 8 or it may be constructed as shown in the drawings, and particularly Fig. 13, giving bearing on both sides of the toothed part of the pinion 8. In the latter case, as shown in Fig. 13, it is necessary to cut away a part of the bushing for the purpose of exposing the teeth of the pinion 8. The mesh of the teeth of the pinion 8 in the rack 3 is adjusted by rotating the eccentric bushing I which is facilitated due to the fact that part of the periphery of the bushing I is knurled. Once the mesh has been adjusted, the adjustment is maintained by tightening the screw 9 shown in Fig. 12.

Pinion 8 is turned by means of the milled head II] which may be keyed to the pinion 8 and held thereon by means of the slotted nut I I. Turning pinion 8 moves the beam I and its attached head 5 and related parts so that the drafting lead 6 is moved with respect to the pivot I2. Pivot I2 is held in the slotted lower end of the housing 4 by means of screw I3. The pivot I2 is sloped as shown so as to provide adequate clamping in housing 4 and at the same time so as to bring the pivot point out from the housing 4 in the direction of the lead 6, thereby making it possible to draw smaller circles than would be the case were the pivot point well under the housing 4. As shown in the accompanying illustrations and particularly in Fig. 19, I use a new form of pivot I2 in which the pivot point 42, Fig. 19, is of the usual pointed or conical form of diameter less than the body of the pivot I2 and protrudes from the fiat bottom end of the pivot, 43, at the same angle from the axis of the pivot I2 as the angle of the recess in the housing 4 in which the pivot i2 is held slopes from the vertical. The point 42 is made at right angles to the flat surface 43. This construction makes the point 42 enter the drawing paper vertically and distributes the load coming on the pivot I2 over the entire fiat surface 43 because it is parallel with the paper surface. This min mizes the damage to the drawing due to the action of the pivot. Since the point 42 is at an angle to the axis of the pivot I2 (as stated, the same angle as the slope of the pivot I2 in the housing 4 from the vertical), a keyway 44 is provided so that the pivot I2 will be properly introduced and held in the seat in housing 4. Any keying means might be employed; but I prefer for its simplicity and ease of construction that which is shown in the accompanying illustrations. By this construction the keyway is simply a flattened surface on one side of the otherwise cylindrical pivot body [2, as shown particularly in Fig. 19; and the recess fo the pivot I2 in the housing 4 is formed by a cylindrical hole and a clamp slot. The slot intercepts the hole in such a way that-the keyway surface 44 rests against one of the fiat walls of the slot while the cylindrical surfaces of the pivot I2 fit against the walls of the hole.

On the pinion 8, at the other end from the milled head III, is the fine scale graduated cylinder I4, which may be held on the pinion 8 by means of a slotted nut I shown in Fig. which draws the graduated cylinder I4 against a shoulder on the pinion 8. The graduated cylinder I4 may be further secured against rotation about the pinion 8 by being keyed thereto. I prefer a quicker means than the nut I5 for holding the cylinder I4 on the pinion, such as the spring clip construction shown in Fig. in which the pinion B terminates in a ball-shaped end 45. Pressure of the spring 46 in the recess below the ball 45 draws the cylinder I4 against the shoulder on pinion 8 and keeps the keyway in the cylinder I4 in engagement with the key 49 in the pinion 8. A screw 41 is provided to hold the spring 46 in the cylinder I4 and two molded lugs 48 reduce the weight of the assembly by making it possible to use a smaller diameter spring and still get the required spring tension. This construction permits rapid interchange of difierent fine scales.

Rotational position of the graduated cylinder I4 about its axis with respect to housing 4 is indicated by a mark on the index I6. This index I6 may be moved about its axis, which coincides with that of graduated cylinder I4, so as to calibrate the instrument's fine scale readings. Once calibration has been made, further movement of index I6 is prevented by the milled nut II upon the stud I8 which is fixed to index I6. With this construction it is a simple matter to calibrate the instrument so that dimensions indicated by it will be in agreement with other scales used by the draftsman in making his drawing.

Housing 4 is slotted at the top so as to permit adjustment of the slidability or tightness of fit of the beam I within housing 4 by means of clamp screw I9. This screw I9 fits into a thread in one side of the slot; but the hole on the other side is clearance drilled to serve merely as a guide for screw I9 whose head does not seat directly against housin 4 but seats against lever 20. One end of lever 20 has a slotted clearance hole through which screw I9 passes, and the other end of the lever 20 has a recessed hole into which the lower end of the milled head I0 fits. The form of the housing 4, and particularly the proportions of metal about the beam I and the form of that part of the exterior of the housing 4 against which lever 20 pivots near milled head I0 (between milled head It and screw I9), is such that turnin clamp screw I9 to tighten and hold the beam I within the housing 4 will first of all introduce friction between lever 26 and milled head I0 before beam I is clamped tight in housing 4. In tightening clamp screw I9 against lever 20 which is pivoted against the outside of. housing 4 between screw i9 and milled head I0 lifts the end of lever 20 which is under milled head Ill outward against milled head ID. This draws the shoulder on pinion 8, shown in Fig. 10, against the adjusting bushing i. As it is upon the outer periphery of this shoulder on pinion 8 that index I6 is centered, the clamping operation does not prevent the calibration of the instrument. Since the clamping operation automatically clamp first the milled head I0 before beam I with rack 3 is stopped from movement in housing 4, accidental damage to teeth of either pinion 8 or rack 3 is prevented. 1

A detachable handle 2| in the top of the housing 4 is provided for operating the compass. The top of the handle 2| is preferably terminated in a head having knobs of large and small diameter, 22 and 23; and the head 2223 preferably has its axis coincident with a line at right angles to the beam I and passing through the point 42 of the pivot I2. This is accomplished by the curved construction shown in Fig. 1. By having the handle 2| quickly detachable it may be readily dismounted and the instrument may be packed in a relatively small case. I prefer a tubular construction for the handle 2| and hollow head 2223, all of one of the light, strong alloys of aluminum, and with the lower threaded end of the handle 2I slotted to permit the through passage of a screw 4I across a slotted and threaded boss on the top of the housing 4. The construction described gives an operating handle that is quickly attached or detached, that is securely held in the instrument, that is properly located with respect tothe vertical axis of the instrument, and that (by means of the large and small knobs 22 and 23) gives good control and operation in the drawing of large and small circles.

Experience with drafting compasses now on the market discloses two elements of time loss in the lead holding devices commonly used. Proper oporation of compasses, especially when drawing circles of small diameter, requires that the lead and the pivot extend the same amount from the instrument. That is, with the compasses closed, the point of the lead and the heel of the pivot should coincide. As the lead wears, either from drawing or sharpening, readjustment is required. The usual practice is to open the clamp and withdraw the lead a little more than required and then, after tightening the clamp, obtain the exact length ef lead required by sharpening. Frequently the lead rotates part of a turn in the withdrawing process and this increases the amount of material to be worn awa in. order to adjust the lead. The faults are all the more apparent in a measuring compass where accurate measurements are dependent on precise adjustment of the drawing lead, even in large diameters. But these faults are apparent in all compasses. In the present invention they are corrected by providing an adjusting device separate from the lead clamp and providing means to prevent the rotation of the lead when it is being moved in or out of the clamp. Further analysis of the problem indicates that the lead itself as generally used is not quite logical in its shape. The lead is cylindrical and is usually sharpened by grinding down the outer side (that away from the pivot) so that a point is obtained that represents the intersection between a cylinder and a sloping plane as shown in Fig. 1. This gives point contact on the paper--essential when drawing very small circles but very quickly destroyed in use and not at all necessary in draw ing large circles. By having the lead with a plane surface on the inside (that toward the pivot) the sharpening operation results in a chisel point that has line contact with the paper and the lead is much more durable. A further improvement presented by this invention is in the construction of the lead clamp which permits the use of various diameters of leads; and further; because the lead is positioned not upon its center but on the sharpened surface, changing the diameter of the lead does not require recalibration of the instrument.

The lead 6 may be held by means commonly used in drafting compasses such as that shown in Fig. 17, but it is referably held by the special means shown in Figs. 1 to 5 and Fig. 16. In either case, one or more elements of the clamping device is faced with one or more serrations 24 running parallel with the axis of the lead 6. Made in this way, when the lead 6 is moved out or in the loosened jaws of the clamping device, it is prevented from rotating about its axis. In the new clamping device shown in Figs. 1 to 5 and Fig. 16, a seat 25 is fixed to the lower end of the tubular member 26 and the lead 6 is held into the seat 25 by means of a clamp jaw 21, actuated by screw 28. Clamp jaw 21 is hinged to the seat 25. As shown in the illustrations, the shape of the seat 25 and the shape of jaw 21 are such that different diameters of lead are held equally well. As shown, both faces of the seat 25 against which the lead 6 is seated are parallel to the vertical axis of the instrument running through the pivot I2. Therefore, for any length of lead 6 extending below seat 25, the distance from the inner side of the lead 6 to the vertical axis will be the same. By sharpening the lead 6 as shown in Fig. 1, which is common practice, the distance from the point of lead 6 from the vertical axis of the instrument will always be the same regardless of the extent of lead 6 below clamp 25. Having the pivot I2 tilted at an angle as has already been mentioned, and by reducing the dimensions of seat 25 to just such as are sufficient for strength in the service required, the instrument can be constructed to include the drawing of very small circles within its range of diameters.

Ordinary cylindrical leads may be satisfactorily used in the instrument but I prefer a lead having the special shape shown in Fig. 22. This lead is of the usual cylindrical shape except for the addition of a key 50 which extends beyond the cylinder. When seated in a suitable clamp, as shown in Fig. 23, the key serves the double purpose of preventing rotation of the lead and causes the usual sharpening method to result in a chisel end rather than a point.

To the tubular member 26 is fixed a rack 29 which meshes with the pinion 30. In this way the lead 6 may be readily brought into proper adjustment; that is, with the point of the lead 6 touching the paper when the pivot I2 is properly seated in the paper and the vertical axis of the compass through the pivot I2 is at right angles to the paper surface. and fitted with a clamp screw 32 so that, once made, the adjustment may be held. This construction obviates the waste of time occasioned by attempting to adjust lead length by means of the clamp and by means of a rather delicate lead sharpening operation.

Head 5 is threaded to receive one end of the long screw 33 which extends through the beam I and draws the pin 34, which is fixed in head 5, into an appropriate seat in the end of beam I, preventing rotation of head 5 about the axis of beam I. When it is desired to extend the range of the instrument, head 5 may be placed in the end of extension bar 35 and held there by means of the extension bar screw 36. The extension bar 35 is also fitted with a pin 34, for the same purpose as that in the head 5. This assembly then takes the place of head 5 in Fig. 1. For mechanical drafting it is preferable to have the instrument without the extension bar constructed with a capacity of -inch circles (diameter), and to construct the extension bars for the instrument to give added capacities in multiples of 10 inches diameter. ,This construction makes it convenient to use the coarse and fine scales of the The head 5 is split instrument as set for use without the extension bar without difficult calculation or re-calibration when an extension bar is used. For example, a reading of 4.56 inches diameter when using the 10-inch additional extension bar would mean an actua1 circle diameter of 14.56 inches. The extension bar construction described and illustrated is light, sturdy, easilyattached or removed, and convenient to use.

Instruments of the general character of that disclosed in this specification have heretofore been graduated merely to show the distance between the points as, for example, the schoolroom measuring compass already mentioned gives the distance between pivot and drawing lead in inches. To draw a circle of required diameter or to indicate a length at a scale other than full size it has been necessary to calculate the required instrument setting. The reason for this is that since detachable scales have not been provided inch-readings have been preferable as reducing calculation where a number of scales may be used. Recognizing the time to be saved in having the instrument give readings direct to any scale, without calculation, this instrument includes quickly detachable scales designed to facilitate drawing circles or indicating distances on drawings, to any scale desired.

The coarse scale 2 is preferably constructed of thin stainless spring steel, hollow ground to fit snugly upon the upper surface of the beam I, and engraved or marked on its convex surface with the desired coarse graduations. Housing 4 is bored to receive beam I and the coarse scale 2 in such a way that the housing 4 will not bind upon scale 2 even when the clamp screw I9 is tightened. One end of coarse scale 2 is constructed with a lug 31 as shown in Fig. 14. This lug 3'I fits into an appropriate slot 38 in the top of the beam I. Graduations on coarse scale 2 are calibrated so as to indicate distance between lead 6 and pivot I 2 according to any desired scale of measurement. The rear face of housing 4 (that is, the face opposite the head of the instrument) may be used as an index by which the position of lead 6 is estimated according to scale 2, or any commonly used pointer or index means may be employed. The hollow ground construction of coarse scale 2, like that of well-known self-supporting steel measuring rules, makes possible the indicated simple method of attaching scale 2 to beam I. When relaxed, the scale is sufficiently stiff to retain its position on the beam I with lug 31 registered in slot 38; but it is sufficiently flexible so that it may be readily removed by bending the lug end of the scale 2 upward so as to withdraw lug 31 from slot 38 when coarse scale 2 may be readily withdrawn from its recess in housing 4 and replaced by another scale 2 having graduations according to a different scale.

For general use, where the instrument is employed for both measuring distances and for drawing dimensioned circles, it is preferable to construct it so that one turn of the graduated cylinder I4 equals one or more full units of length in movement of lead 6 with respect to pivot I2. According to this, and considering proportions necessary to rigidity, a compass for drawing measured distances and circles in the metric system would preferably have one turn of pinion 8 equal to, say, two centimeters movement of lead 6. In the English system, one turn of the pinion 8 would preferably equal one inch movement of lead 6 with respect to pivot I2.

vWith the instrument thus constructed for use in the English system, the measurement and platting of distances to inches and hundredths would be accomplished with a coarse scale 2 di.

vided into inches and a fine scale divided as indicated on the cylinder M in Figs. 2 to 5. To use the instrument to indicate the diameter of circles drawn by it at full-size scale, a coarse scale would be used with divisions spaced at half-inch intervals and a fine scale woull be used divided like that on the cylinder 33 in Fig. 6; that is, with the periphery divided into two identical sets of divisions.

Coarse and fine scales may be provided to combine distance and diameter readings, as by using two colors. For example, the coarse scale 2 may be marked off in two rows of graduations and numbers. One row in, say, red may be graduated every half-inch and numbered consecutively. The other row in, say, black may be graduated every inch and numbered consecutively. The fine scale cylinder would combine the graduation of cylinder 38, in red, with those of M, in black, on a single cylinder. Using the instrument thus constructed in making a full-size drawing to 0.01 inch, the draftsman would set the instrument according to the red graduations for circle diameters, and according to the black graduations for circle radii or straight-line distances.

Again, still having the instrument constructed with the designated ratio of one revolution of pinion 8 per inch movement of lead 6 with respect to pivot l2, were it desired to indicate distances on a map on a scale of 3090 feet per inch, a coarse scale 2 with divisions spaced at three per inch would be med along with a fine scale repeated around the periphery of the graduated cylinder (like It) identically three times in each of which IGGO-foot unit would be shown the desired system of division.

Again in an instrument with the stated gear ratio, if desired to measure distances according to the fraction system, a set of fine graduations numbered as indicated on the graduated cylinder 39 in Fig. '7 would be used.

When the instrument is to be used entirely or almost entirely for drawing dimensioned circles inmachine drawing with diameters expressed in the English system, to fullor less than fullscale, it is preferable that one turn of the pinion 8 equal one-half-inch movement of the lead 6 with respect to the pivot. This construction gives wide divisions in the fine scale on the graduated cylinder I l and reduces somewhat the half-inch intervals along its length, and the periphery of the graduated cylinder 14, representing a single unit of the coarse scale 2, is divided into the fine divisions desired, such as tenths and hundredths shown on cylinder i l in Figs. 2 to 5, or into fractions of an inch as on cylinder 39 in Fig. 7. If a smaller scale is used, such as halfsize scale, then the units along the coarse scale would be proportionately closer together, and the divisions on the graduated cylinder (like M) would be proportionately finer and repeated a proportionate number of times around the periphery as indicated by cylinder 38 in Fig. 6.

Scaling distances or drawing measured circles on a scale greater than the maximum for which the instrument is constructed for general use may be accomplished by either (a) using an ordinary coarse and corresponding fine scale and getting the readings necessary to give the desired dimensions either by computation or by using a table of equivalents; or (b) using a graduated cylinder having sets of different graduation figures repeated in columns adjacent one another along the axis of the cylinder, each column ,being in a distinct color corresponding to an area along the coarse scale given the same color, in which measurement range the figures of that column are to be used, and alternating the colors along the coarse scale so as to correspond in each case to the proper figures of the fine scale. For example, if the instrument is constructed so that one turn of the pinion 8 moves the lead 6 one inch and scales are desired so that distances will be measured on a scale of twice full-size in the decimal system, the cylinder may be divided into 50 equal parts with every tenth line indicated twice by numbers in two adjacent columns. In the first column the figures are black, and they run consecutively from 0 to 4. In the second column the figures are red, 5 is on the same line as the black 0, and the numbers run consecutively from 5 to 0. The first inch on the coarse scale is black, the second inch is red, and the numeral 1 appears at the second inch mark. Black and red stretches of one inch each alternate through the length of the coarse scale, and every second inch mark is numbered consecutively.

To prepare the instrument for use the handle is first fixed to the housing 4. Coarse and fine scales are then chosen according to the scale of the drawing being made, and these are attached to the instrument in the manner already described. The lead adjusting nut 32 is loosened and the lead adjusting pinion 36 is turned to raise the lead clamp 25. A lead 6 is clamped in place on the clamp seat 25 and sharpened in the usual manner as indicated in Fig. 1. Following this, all subsequent adjustments of the instrument, including the adjustment of the lead in between re placement in the lead clamp 25, may be made with the left hand alone while the'instrument is held by the head 2322 in the fingers of the right hand. Pinion .30 is turned to adjust the lead 6 as has already been described. Clamp screw [9 is loosened and the instrument is calibrated according to the scale being used for straight lines on the drawing being made. This is done by turning the milled head iti so that the distance from lead 8 to pivot i2 is a certain distance according to the scale being used for calibrating, say four inches. Clamp screw I9 is tightened. Calibration clam-p nut I1 is loosened, calibration disk i6 is turned until the index mark coincides with the zero on the graduated cylinder l4, and the nut I1 is tightened again. Clamp screw I9 is loosened and the milled head I0 is turned until the coarse and fine scales indicate desired dimension or circle diameter when clamp screw I9 is again tightened. The circle is then drawn by turning the instrument with the head 2223 in the fingers of the right hand. Small circles are best drawn by spinning the instrument, using the knob 23. The larger diameter 22 is more useful when drawing circles of larger diameter or in drawing segments of circles of any diameter.

Examination and test of a compass made according to this specification disclose the following: It Weighs a fraction of an ounce more than one of the so-called giant-bow compasses which are in common use for drawings rendered for reproduction from pencil direct without inking. The new compass draws circles nearly two inches larger in diameter than is possible with the giant-bow. Throughout its range, the opaqueness and uniformity of lines drawn with it are equal or superior to those of the giant-bow. In a comparative test involving the drawing of a number of circles the new compass drew the same set of circles in 44% less time'than was possible with the giant-bow, and drew all of them more accurately. In a longer test involving adjusting and sharpening lead, the new compass showed a saving in time of over 50%; that is, it drew more accurate circles and drew them more than twice as fast.

It is obvious and it is anticipated that some of the details disclosed in this specification are applicable to and may be used in compasses of types other than measuring compasses, and may be used in entirely different arts. Moreover, while I have illustrated and described the preferred form of construction, I do not wish to limit myself to the precise details of structure shown in the drawings but desire to avail myself of such variations and modifications as come within the scope of the appended claims.

I claim: I

l. A drafting compass consisting of an elongated toothed bar, a longitudinal scale fitted to the bar, a housing with a hole to receive and give a sliding fit for the bar and the longitudinal scale, rotatable means meshing with the teeth of the bar for moving the bar with respect to the housing, means for adjusting the mesh between the rotatable means and the bar, means for indicating the relative rotation of the rotatable means with respect to the housing, a pivot in the base of the housing, means in the top of the housing for holding and rotating the compass about the vertical axis of the instrument through the pivot, a guide at one end of the bar for holding and permitting the vertical motion-of a slide, a slide in said guide and means for moving the slide in the guide, a drawing means and means on the slide for holding said drawing means.

2. A drafting compass consisting of an elongated substantially horizontal bar with a toothed rack formed thereon whose length is parallel to the length of the bar, a detachable longitudinal scale fitted to the bar, a housing bored with a hole to receive and give a sliding fit to the bar, rack, and longitudinal scale, an eccentrically bored cylindrical bushing rotatably mounted in said housing, a pinion freely rotatable in said bore in said bushing, the axes of the bushing and bore being parallel, the teeth of the pinion being meshed with those of the rack, a detachable cylindrical scale mounted on the pinion, an index to indicate relative rotational positions of the cylindrical scale, means for moving and holding the index, a pivot in the bottom of the housing,

a handle on top of the housing, a head at one end of the bar, means for holding the head to the bar, a vertical slotted guide hole in the head and a rack slidably mounted therein, a pinion rotatably mounted in the head and meshing with said rack, means for locking the rack in th head in any desired position, and means mounted on said rack for drawinglines.

3. A drafting compass according to claim 1 having a clamping means which, when tightened, automatically clamps the bar within the housing and clamps the rotatable means in locked position,

4. A pushing and pulling device consisting of a rod having a toothed rack fixed thereto, said toothed rack being substantially parallel to the axis of said rod, a housing having a passage to slidably accommodate said rod and rack, means to maintain the rod fixed inany desired position with respect to said housing, a rotatable pinion operatively engaging said rack, and movable means associated with said device and actuated by said rotatable pinion to indicate the amount of relative movement between said rod and housing.

5. A pushing and pulling device consisting of a rod having a toothed rack thereon, a housing having a passage to slidably accommodate said rod and rack, a rotatable pinion operatively engaging said rack and adapted to move said bar with respect to said housing, and clamping means on said device operable to simultaneously clamp said bar with respect to said housing and said pinion against rotation.

6. A pushing and pulling device consisting of an elongated bar upon which is formed a toothed I rack which is parallel to the axis of said bar, a

housing having a hole therein to receive and atford sliding movement of said bar in the direction of its axis, a slot in said housing approximately parallel with the bar and extending from the outer surface of the housing inwardly to and intersecting the wall of said hole, said housing face of said housing, a lever located on the exterior of the housing and having an aperture to receive said screw and also a portion engaging said annular shoulder between it and the housing, the head of said screw, upon being threaded inwardly, serving to fulcrum the lever about the housing and cause the lever to frictionally engage the annular shoulder to maintain the pinion against rotation and also clamp the housing against the bar.

'7. A drafting compass comprising a housing, a pivot extending downwardly therefrom, a handle extending upwardly therefrom, a bore extending horizontally therethrough in position of use, a bar slidably mounted in said bore, a gear rack disposed on said bar, a gear rotatably mounted in said housing and meshing with said gear, means to rotate said gear, and move said bar longitudinally in said bore, said bar having a longitudinally disposed opening therethrough, an elongated bolt disposed therein, a head adapted to be mounted on one end of said bar and supporting a drawing member, said head having a threaded aperture to receive one end of said bolt to clamp said head against the end of said bar, a tubular extension bar adapted to be inserted between said head and its adjacent bar end and an extension bolt adapted to be threadably fixed to said first bolt and received in said extension bar whereby one end of said extension bolt will engage the threaded aperture of said head and, upon rotation of the bolt assembly, serve to draw the head, extension bar, and bar into assembled position for use, said head and bars having key means to maintain the head and drafting member in vertical position in use.

8. A clamp for holding drawing leads in drafting compasses and the like comprising a substantially plane surface at right angles to a line from the points of the pivot and the lead, and means for holding the lead against the surface of said plane.

9. In a drafting compass, a chuck for holding the lead thereof having one or more serrations parallel to the length of the lead received therein, and means to clamp said lead thereagainst to prevent rotation of the lead about its axis.

10. A chuck for holding bodies having the general shape of an elongated cylinder consisting of a seat formed by the intersection of two planes against which portions of the cylinder may rest, a clamp jaw movable with respect to one of the planes and having a clamping face to contact a portion of said cylinder and press the cylinder in the direction of said plane intersection, and means for moving the clamp jaw in that direction.

11. A chuck according to claim having serrations on said clamping face.

12. A chuck for holding objects of general cylindrical shape consisting of blocks shaped and arranged to form between them a recess which prior to clamping action approximately equals the diameter of the object, means for drawing the blocks together in a direction which will clamp them upon an object in the recess; and one or mor elongated serrations formed on and projecting radially from the recess-forming face of one or more of the blocks, said serrations being parallel to the longitudinal axis of the object being clamped,

13. A drafting compass consisting of a pivot, drawing means, means for maintaining a desired distance between the pivot and the drawing means, means for positively adjusting the relative position of pivot and drawing means with respect to a plane perpendicular to the vertical axis of the instrument through the pivot, indicating means comprising a scale which may be replaced by others of different scales of measurement connected to said compass to indicate the distance between the drawing means and pivot at any setting of the same, and quick-acting means to detachably secure said scale to said compass comprising resilient means and means to engage said resilient means, said means being disposed one on the scale and the other on the compass.

14. A drafting compass consisting of a pivot, drawing means, means for maintaining a desired distance between the pivot and th drawing means, means for positively adjusting the relative position of pivot and drawing means with respect to a plane perpendicular to the vertical axis of the instrument through the pivot, and indicating means comprising a rotatable member movable by said adjusting means, a cylindrical scale member mounted on said rotatable member by snap fastener means, means to maintain said rotatable member and scale member in rotary alignment, whereby cylindrical scales bearing different characteristic may be readily interchanged and mounted on said rotatable member to indicate the distance between the drawing means and pivot at any desired setting of the same.

15. A drafting compass comprising a support, a pivot and head member attached to said support, a member slidably supported by said head, a drafting member adjustably connected to said member, mean carried by said head to move said drafting supporting member with respect to said head and means carried by said member to move said drafting member with respect to said member slidably supported by said head in a line substantially parallel to the axis of said pivot.

16. A drafting compass comprising in combination, a pivot, drawing means, means for maintaining a desired distance between the pivot and drawing means, means for positively adjusting the relative position of the pivot and drawing means with respect to a plane perpendicular to the vertical axis of the instrument through the pivot, and indicating means comprising a scale adapted to be replaced by other scales of different measuring characteristics and detachably connected to said compass to indicate the distance between the drawing means and the pivot at any setting of the same, said detachable connecting means comprising spring means on said scale and means on said compass to engage said spring means.

LEW SUVERKROP.

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