Patent GB-494931-A (GB)
Title: Improved manufacture of gears
IPC: B23F19/02
Filed: 1937-11-30
Abstract: 494,931. Grinding gear-wheels. TENNANT, W. J. (Gleason Works) Nov. 30, 1937, No. 33113. [Class 60] [Also in Groups XXII and XXIV] A tapered gear such as a bevel or hypoid gear has longitudinally curved teeth whose side surfaces are parts of involute helical surfaces, and is cut by a taper hob having involute helical thread surfaces which is fed to depth while the hob and blank are rotated in unison. The tool may also take the form of a burnishing, lapping or shaving tool for finishing operations, the teeth of a shaving gear being suitably gashed. In Figs. 1 and 2 a tapered gear having teeth of substantially uniform depth, a pitch cone apex 20, and axis 26 is shown. It is shown that a tapered worm member 50 having involute helical thread surfaces will mesh correctly with both sides of the teeth of the gear shown in Fig. 2 the sides 51, 52 being generated by straight lines maintained tangential to the basic cylinders 53, 54 respectively while they are simultaneously rotated about axis 55 and moved axially to the direction of said axis. Such worm threads are of straight-sided section in a plane tangential to the basic cylinder but of curved section in an axial plane. The hob formed from this worm is used to form the gear 60 being fed to depth preferably in the direction of axis 61 of the gear. There may also be a feed along the pitch cone generator 62 of the tool in order to obtain a smoother finish to the work, this movement being compensated by modified rotation of the hob or blank. For this purpose the machine described in U.S.A. Specification 1,647,158 is modified as shown in Fig. 8, the feed along line 62 being derived from a screw 78 driven through reduction gearing from the shaft 75 which drives the hob. For burnishing, an ungashed taper worm is rotated in mesh with the blank and drives the blank through their meshing engagement. No special compensation is required if feed along the line 62 is employed. For lapping operations correcting motions may be used to maintain the shape of the lap. Such motions may comprise a slow reciprocation along the line 62 or a motion along the axis 61. Preferably a clearance is provided at the bottom of the lap thread to permit this latter movement. Or these two motions may be combined in which case they have different periods of which neither is a multiple of the other. Formulae are given in the Specification for determining the various dimensions of the tool and its setting in relation to the blank. The sides of the tool threads may be produced by straight-sided cutting-tools positioned in planes 85, 86, Fig. 5, which are tangential to the base cylinders 54, 53 respectively, the blank being rotated and tool moved at a determined speed along line 62. The tool may also be formed by a straight sided milling- cutter or grinding-wheel. It is shown that in the case where the normal pitch is the same for both sides of the teeth, the same hob may be used for both gear and pinion. For lapping the pinion, it is preferably run with a cast iron lap of mate gear form but alternatively the lap may be of the same form as the taper worm cutting-tool. The lap may be reciprocated axially to reduce wear.