US2557500A - Drawing compass - Google Patents

Description

June 19, 1951 c. 1 FAIRBANKS DRAWING COMPASS Filed June 19, 1948,

.f 1 1 l x, m3 v l .1. p IafgffI Z4 INVENTY'OR.

CARL LFA/RBANKS a i t l @$51116 Patented June 19, 1951 UNITED s'rATEs TENT OFFICE 1 Claim.

The present invention relates to drawing compa'sses of the general type having a yieldably mounted spring-urged pivot point for facilitating use of the instrument in drawing or scribing small circles. An object of the invention is to provide an improved drawing compass of this character in which the downward spring pressure on the yieldably mounted pivot point can easily and quickly be adjusted, and in which the pivot .point can readily be held or locked against yielding, as when the compass is used for drawing large circles.

Another object is to provide a drawing coinpass of this type having a readily accessible adjusting member which serves to adjust the spring pressure on the pivot point and also serves to lock the pivot point against yielding.

Still another object-is to embody the springurged pivot point and its associated parts in a simple, durable and inexpensive self-contained attachment or unit which can easily be applied or clamped to most standard Compasses, `such as bow pencils or pens, in place offthe usual fixed pivot point.

A further object is to perfect details of construction generally. Y

The invention further consists in the several features hereinafter described and claimed` In the accompanying drawing, illustrating certain embodiments of the invention,

Fig. 1 is aside elevation of a drawing compass of the bow pencil type arranged in accordance with the invention;

Fig. 2 is a transverse sectional view taken on the line 2-2 of Fig. 1;

Fig. 3 is an enlarged longitudinal sectional view of the pivot point attachment or unit;

Fig. 4 is an exploded View of the pivot point attachment, and

Fig. 5 is a view generally similar to Fig. 3, showing a modilied form of pivot point attachment.

Referring to the drawing, Fig. l illustrates a drawing compass, here shown by way of example to be a bow pencil, which is of conventional construction except for the pivot point mounting hereinafter described. The compass comprises a pair of legs I Il and Il which are hinged at their upper ends, the hinge connection including a pivot pin IZ carrying the usual knurled handle stem I3. The legs are held against the pivot pin at their upper ends, and urged -apart at their lower ends, by a looped leaf spring I engaging the upper ends of the legs; and the spread of the legs is adjusted by a screw I5 threaded through trunnion nuts I6 on the legs and provided with a central knurled thumb wheel I1. The lower end 0f each compass leg is longitudinally split and grooved and forms the usual clamping socket or chuck I8, each split leg end being provided with the usual transversely extending clamping screw I9. Each split leg socket extends along the outer side of theleg and is open at its upper and lower ends. The clamping sockets of the two legs converge downwardly at a small angle when the legs are at their inner range of their adjustment. A scribing point or stylus 20, such as a pencil lead, is clamped in the Split socket of the leg I I.

In a conventional compass the split socketv of the leg I0 carries a .fixed pivot point, but in the present instance this point is removed and is replaced by the device or attachment of the present invention-This device comprises a thinwalled metal tube consisting of upper and lower cylindrical sections 2l and 22, the latter being of smaller diameter than the former and being adjustably clamped in the split socket `I8 of the compass leg I I. A rod-like pivot point 23 is slidably mounted in the lower tube section 22 and has a downwardly projecting lower end portion with a sharpened tip 24 adapted to penetrate the drawing paper or other drawing surface. The pivot point has an upper coaxial extension 25 which is centrally disposed in the upper tube section 2l The pivot point also has an annular liange or rib 2E at the lower end of the extension 25 adapted to seat against an annular stop shoulder 21 formed in the tube at the junctions of the upper and lower tube sections. A light coiled spring 28 housed in the upper tube section 2l has its lower end bearing against the pivot point flange 26. The spring is placed under adjustable compression by a thumb screw 29 which is threaded into the upper end of the upper tube section 2| and bears against the upper end of the spring. The cylindrical upper end of the pivot point extension 25 is slidably guided in an axial bore 30 formed in the thumb screw 29. The closed upper end SI of this bore is adapted to bear on the upper end of the point extension 25 when the screw is turned inwardly, thus locking the pivot point against shifting when this relation is desired, as when the compass is used for drawing large circles. By backing off the thumb screw slightly from its point-locking position,.the sliding travel of the pivot point may be adjustably limited. The point extension 25 serves to guide the coiled spring.

In the use of the compass, the tip 24 of the resiliently mounted pivot point is placed against the drawing paper at a desired location and the compass is urged vertically downward by its handle I3, causing the tip to penetrate the paper slightly and bringing the scribing point 20 against the paper, whereupon the compass is revolved about the pivot point tip to scribe a circle. As the pivot point tip is held rmly against the paper by spring pressure there is no danger of slipping. To scribe a dotted circle, the rotating compass, with its scribing point, is allowed to rise periodically by reducing the downward manual pressure on the compass handle, the spring-urged pivot point remaining in firm contact withY the paper. As the scribing point wears, the tube section 22 moves down a little farther over the spring-urged pivot point, thus compensating for the Wear, making it unnecessary to tilt the compass and avoiding excessive penetration of` the pivot point into the paper. If adjustment of spring pressure-is desired, thiszis effected by turning the readily-accessible thumb screw 2.9. When the compass is to be used for scribing large circles, it is desirable to lock` the pivot point against longitudinal displacement, as above described, in order to avoid variations in the scribing radius.

The compass` illustrated is a bow pencil but it will be understood` that thev pivot point attachment of the invention may also be applied to a bowv pen. The invention is also applicable to Compasses of the parallel leg type.

In the modified formof device shown in Fig. 5, a pivot point 23 is slidable in the lower tube section 22 and terminates` at its upper end in a headl 2.6.l engageable with the tube stop shoulder 2T. A coiled spring 28 housed in the upper tube section 2|y bears on the head 26', and a thumb screw 29. adjustably threaded into the upper end of the upper tube section 2| bears on the upper end. of the spring and has a downwardly prolecting axial stop stem 32 within the spring, the lower end of the stem being'engageable with the head; The device of Fig. 5y is otherwise similar to that of Fig. 3 and is used in the same manner.

If the. pivot pin extension 25 of Fig. 3, or the thumb screw stem 32 of Fig. 5, is shortened or omitted:I it' would' be possible to lock the pivot pin by compressing the coiled spring solid. However, the locking means illustrated provides a more definite locking action, permits a wide rango of spring adjustment, simplifies design of the spring, and avoids possible overstressing of the sprlng.

What I claim as new and desire to secure by Letters Patent is:

In a drawing compass having a pair of relatively movable legs one with a' scriber at its lower end, a tubular housing on the lower end of the other leg, an upwardly yieldable pivot point slidable in said housing and projecting downwardly therefrom, a coiled compression spring in said housing engaging said pivot point and urging said point downwardly, stop means limiting the downward displacement of said pivot point inV said housing, and a screw-threaded springconfining member having a screwed engagement with the upper portion of said housing and movable axially thereof to different selected positions, said member having a central bore loosely guiding the upper end of said pivot point and further having an abutment surface in the path of the upper end of said point and engageable with said pointend for adjustably limiting the inward displacement of said point, andsaid member when screwed downwardly to its lowermost position having said abutment surface in engagement with said point end and locking the projecting point. against said stop means.

CARL L. FAIRBANKS.

REFERENCES CITED TheV following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 800,257 Abetz Sept. 26, 1905 992,819 Springer May 23, 1911 1,779,725 Bell Oct. 28, 1930 2,104,515 Golden Jan. 4, 1938 2,278,440 Graves Apr. 7, 1942 2,442,185 Szerenyl May 25, 1948

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