GB356186A - Improvements in or relating to screw-cutting chasers - Google Patents

Abstract

356,186. Screwing die-heads. JONES & LAMSON MACHINE CO., Springfield, Vermont, U.S.A.-(Assignees of Bysshe, E. T. ; 91, Summer Street, and Finn, R. R. ; 98, Wall Street, both in Springfield, Vermont, U.S.A.) April 29, 1930, No. 13224. Convention date, May 15, 1929. [Class 83 (iii).] Chasers.-Screw-cutting chasers, of the tangent type, have a number of concave surfaces on the grooved side so that the grooves on the chaser are in contact with the threads on the work over a definite arc, and the concavities may be brought into use successively on regrinding of the chaser. Each chaser of a set in a die-head has a plane gauging surface 2 for engagement with a corresponding surface on the head and is provided with a dovetailed projection 4, accurately ground and lapped to fit the head. Accurately formed ratchet teeth 6 on the projection 4 preferably co-operate with the gauging mechanism described in Specification 356,223 to allow the cutting edge 16 to be adjusted to the same position in the head after wear and regrinding. The work-engaging face is grooved at 3 at the correct thread angle, the teeth up to a being bevelled off to provide cutting teeth of gradually increasing depth whilst the remaining teeth are of full section and act as screwing guides only. The cutting teeth are provided with a series of concave surfaces 7 by means of a threaded lap of substantially the same diameter as the work, these teeth being formed originally outstanding from the guide teeth so that after lapping their deepest portions are in the same plane as the valleys of the guide teeth. The end surface 7 in engagement with the work enables all the cutting edges to meet the work tangentially even if the chaser is provided with top rake whilst the remaining cavities are used successively when the end one has been ground away. The guide teeth project beyond the cutting teeth so that their ends do not engage the work. In a modification the cavities 201, Fig. 8, extend across all the teeth and are formed by a lap 21 of larger diameter than the work 22 but arranged on an oblique axis as shown to preserve the same thread angle on the chaser. In this case also the guide teeth from a to the gauging face 210 project beyond the cutting teeth so that the guide teeth are out of contact with the work on their extreme ends. In a further modification each chaser consists of a disc 40, Fig. 10, cut away at 42 to provide a cutting edge 43 and secured by a central screw 44 to an angularly adjustable shaft 45 in the head, radial serrations 47 on the disc and shaft preventing relative rotation thereof. The shaft is adjusted angularly by a worm 49 to compensate for wear and grinding of the cutting edge. Cavities are formed on the cutting teeth only, as in Fig. 4, or on all the teeth as in Fig. 8, in each case the first teeth only being the cutting teeth. Fours discs 40 are preferably arranged around the work.