GB565443A - Improvements in toothed gearing and in the manufacture thereof - Google Patents

Abstract

565,443. Gear-cutting. GUEST, J. J. July 30, 1943, No. 12436. [Class 83 (iii)] In a method and apparatus for generating the teeth of gears having .non-circular pitch lines and whose mating pairs have parallel axes, without using a gear of the type to be produced as a master gear, the relative movement of a hob or rack cutter and the gear blank is controlled by the relative movement of a disc shaped to the required non-circular pitch line and a plane upon which the disc is made to roll without slipping, According to one method the gear blank is mounted on a pivot 24, Fig. 2, coaxial with a disc having a periphery 21 ... 23 shaped to the curve of the required pitch surface and connected to a flat surface 25 by flexible bands so as to roll thereon. The pivot 24 is carried by an arm 27 pivoted at 28 in the same plane as the surface 25, which is traversed to rotate the blank, a rack cutter being reciprocated to cut the teeth and simultaneously moved tangentially to the blank at the same speed as the surface 25, and being indexed relatively to the blank if too short to cut all the teeth in one traverse. In a modification, the control disc 31 ... 33, Fig. 3, is made larger than the work-piece and is pivoted at 34 on a member 41 adjustable along a lever 37 pivoted at 38 to the machine frame and having the work pivoted thereto at 39, the ratio of the distances 38, 34 and 38, 39 being the same as the ratio of the control disc dimensions to those of the work. The disc and work are connected by equal gears 42, 43 and an idler 44 so that they both rotate through equal angles. The control disc rolls on a freely rotatable plate 47 and one flexible band-is connected to a tensioning weight 46 whilst the other is attached to a drum 45 rotated in synchronism with the traverse of the rack cutter 52, which is relieved from the work on the return strokes. The drive for the longitudinal traverse of the cutter includes a helical cam 53 which, together with a gauging stop 55, indexes the cutter periodically through one or more pitch distances, a differential gear 56 being interposed in the drive 51 from the drum 45 to the cam 53 to allow for adjustment of the cutter along its pitch line by rotation of the planet pinion carrier. The pivot 39 may also be adjustable on the lever 37 to allow a larger ratio to be used of the control disc to the work, and for cutting short toothed segments, indexing may be dispensed with. The cutter 52 may be replaced by a hob rotating on an axis inclined to the line of travel of the plate 47 at the pitch angle and reciprocated continuously across the teeth being cut. In a further modification, wherein two work-pieces may be cut simultaneously, the control discs are pivoted at 61, 611 respectively, Fig. 4, on an arm 62 slidable through a guide 74 pivoted on trunnions 75 coaxial with the pitch point 68 of the discs. The pivots 61, 611 are carried by pantagraphs pivoted to the machine frame at 63, 631 and having the work-pieces pivoted thereto at 64, 641 so as to give the correct ratio of reduction from the enlarged control discs. The discs and work are' connected by gearing 66 mounted on the pantagraphs so as to rotate through equal angles. The discs are placed side by side so as to roll on adjacent opposed surfaces 71, 711, one flexible band from each disc being connected to a driving drum 73 and the others being attached to weights at 79 or being positively controlled by a second driven drum. The plate 47 may be adjusted axially to allow the blank to be moved away from the cutter when taking roughing cuts, and a disc-type cutter may be used instead of a hob or rack cutter.