GB552600A

GB552600A - Hob for generating crown gears

Info

Publication number: GB552600A
Application number: GB15523/41A
Authority: GB
Original assignee: Fellows Gear Shaper Co
Current assignee: Fellows Gear Shaper Co
Priority date: 1940-12-14
Filing date: 1941-12-02
Publication date: 1943-04-15

Abstract

552,600. Gear cutting. FELLOWS GEAR SHAPER CO. Dec. 2, 1941, No. 15523. Conven. tion date, Dec. 14, 1940. [Class 83 (iii)] A bobbing cutter 10 particularly for generating a crown gear 11 conjugate to a spur pinion but applicable also for generating spur or helical gears or straight or helical internal gears has the teeth arranged in helical convolutions around the tool axis A, the teeth in adjacent convolutions being radially arranged along a circular arc, Fig. 3, whose centre of curvature 16 lies between the end faces of the tool. The crown gear blank 11 has a tooth bearing rib 12 and is adapted to mesh with a spur gear having an axis 15 intersecting the crown gear axis at right angles. At the outside diameter of the crown gear, the pinion teeth engage with a pitch circle PC, Fig. 4, LA being the line of action and M the length of action. At the inner end the teeth have a smaller pitch circle giving a smaller pressure angle and increased length of action. The hob teeth in Fig. 3, which shows a section normal to the tooth helix, are of involute form and are arranged on a base circle BC of the same radius as the base circle BC in Fig. 4. The hob teeth have longer addenda at their cutting ends for cutting clearances in the work and have the usual top and side relief. The base surface of the hob considered as a whole Is thus a toric surface generated by revolution of the arc BC round the hob axis A. Preferably the teeth are arranged on a single thread helix. In operation the median plane of the hob is offset from the blank axis so as to bring the teeth in the middle of the hob substantially radial of the blank when in the cutting zone. The hob and blank are then rotated in timed relation, and the hob fed radially of the blank. The teeth in the mid zone of the hob engage first and when the Fig. 1 position is reached the outer ends of the teeth are completely generated. The feed is continued until, when the position shown in Fig. 5 is reached, the operation is finished.