Patent GB-594824-A (GB)
Title: Improvements in or relating to machines for grinding hobs
IPC: B24B3/12
Filed: 1944-11-16
Abstract: 594,824. Grinding hobs. MICHIGAN TOOL CO. Nov. 16, 1944, No. 22712. Convention date, Nov. 26, 1943. [Class 60] Apparatus for side relieving the teeth of hobs comprises a rotatable main table adapted to rotate about an axis perpendicular to the axis of rotation of a rotatable hob support and in synchronism therewith, and a grinding tool positioned to engage the side of the hob teeth mounted on a second table for rotary movement therewith, the second table being mounted on the main table for rotation therewith and driven thereby through the intervention of a driving connection adapted to retard and advance the rotative movement of the second table relative to the main table for effecting the relief on the teeth. The driving connection preferably comprises a resiliently-urged member on one of the tables and a shiftable cam member mounted on the other table and engageable with the resilient member, the shiftable cam member being adapted to be shifted independently of means for rotating the hob support and the main table in synchronism. The invention is described with reference to grinding side relief on the teeth of hobs of the enveloping type, that is, hobs designed for use in cutting the worm-wheel or worm gears of gear sets embodying the Hindley or globoidal principle. Fig. 9 illustrates such a hob, of the type disclosed in Specification 362,448, [Group XXII], and having several threads. Each tooth has a cutting edge 20, and relief is provided on the side 22 of each tooth by a machine as illustrated in Fig. 1. The hob 10 is mounted horizontally between a headstock and adjustable, by hand wheel, horizontally on the machine frame 24. The grinding tool comprises a small cylindrical pencil grinding element 36 carried, by slides permitting adjustment vertically and in two horizontal directions at right angles, on an auxiliary table 30 mounted on a table 26 rotatable about a vertical axis. The grinding element is belt-driven by a motor 56 pivotally mounted on the end of a double crank. The auxiliary table 30 has secured to its undersurface a plate member 120, Fig. 3, having a depending member 124. Fig. 5, with a sloping cam edge 126 engaged by a cam edge 136 on a rod member 128 mounted in a radial bore in the main table 26 ; the table 26 also carries a spring 140 which forces the member 124 into abutment with the end of the rod 128 so that the auxiliary table 30 rotates with the main table 26 ; to effect side relief, the auxiliary table is caused to lag progressively behind the main table, and to cause this the rod 128 is moved radially outwards by vertical movement of a rod 50 by a cam 162. The cam is rotated once for every tooth and in synchronism with the rotation of the hob and main table, so that the lag, and hence the side relief, is progressive for each tooth of the hob. The headstock for rotating the hob is driven, Fig. 8, by a variablespeed reversible motor 210 by way of belt 204, clutch 200, gears 196, 194, worm gear 188 and worm 190, shaft 182, worm gear 184 and worm 186; both sets of worm and worm gear are preferably of the double enveloping type described in U.S.A. Specification 1,822,800. The main table 26 is driven from shaft 182 through gears 214, 216, 218, 220, matching differential 224, worm 258 and worm gear 84, the latter gears being also of the type described in U.S.A. Specification 1,822,800. The matching differential 224 is employed for the purpose of providing relative side feed of the grinding element with respect to the hobs so that the grinding element may be properly set for its initial engagement ; it comprises gears 228 and 230 keyed respectively to shafts 222 and 212, and an idler gear 232 in a housing 226. The gears 228 and 230 have the same outside diameter, but gear 228 has less teeth than gear 230 ; e.g. gear 230 has twenty-four teeth, gear 232 has thirteen teeth and gear 228 has twentythree teeth, the centre distances for gears 228 and 230 with respect to gear 232 being the same, the twenty-four tooth gear being standard while the twenty-three tooth gear is cut to mate with the thirteen tooth gear. The housing 226 can be rotated by means of a hand wheel 242. Specification 580,747, [Group XXII], is referred to. The cam for imparting side relief is driven from shaft 182 through gears 292, 294, 298, 300, 302, 304, bevel gears 286, a one-way drive 270 and bevel gears 264 ; owing to the one-way drive, the cam is rotated only when the table is rotating in one direction, but not when it is rotating in the opposite direction, during which motion the grinding element returns through the space between the rows of teeth to its original position. U.S.A. Specification 1,980,444 also is referred to.