Patent GB-425193-A (GB)
Title: Improvements in methods of and apparatus for cutting worms
IPC: B23F13/06
Filed: 1934-02-12
Abstract: 425,193. Gear-cutting. MILLER, E. W., 9, Elm Street, Springfield, and FELLOWS GEAR SHAPER CO., Springfield, Vermont, U.S.A. Feb. 12, 1934, No. 4556. Addition to 375,876. [Class 83 (iii)] The method of cutting gears described in the parent Specification is adapted to the generating of globoid worms. The work piece 30 is generated by a cutter 28, Fig. 14, of gear-wheel form located with its axis transverse to the blank axis, the cutter and blank are rotated in timed relation, and the cutter is oscillated additionally through distances equal to the distance between the pitch-line width of the teeth and the finished width on the pitch-line of the worm gear spaces. As wear on the cutter occurs and its teeth are consequently thinned, the amplitude of this additional movement is increased so that spaces of full width are cut in the work throughout the life of the cutter while maintaining a fixed distance between the cutter and blank axes. The machine bed has guides 24, Fig. 5, for a saddle 26 carrying the vertical cutter spindle 27 fitted with a cutter 28. The latter has relieved helical teeth with helix angle complemental to that of the worm to be cut. The cutter teeth are of the same pitch and their side faces have the same form as the gear with which the worm to be cut is to mesh, but have greater radial length to allow for sharpening the cutter. The cutter teeth may be of involute or other form, such as the straightsided form shown in Fig. 16. The blank 30, Fig. 2, is mounted on a taper-shank arbor 31 seated in a spindle 32 mounted in bearings 34, 35, the arbor being steadied by an outer bearing 36. The work-spindle is driven from a motor 40 through a belt 39. A gear 41 on the work-spindle is connected through a gear 42, and vertical spindle 44, shaft 45, spur gears 48, and worm 51 to a worm wheel 52 splined to the cutter-spindle which is thus driven in timed relation with the blank. The cutter may be fed to depth either tangentially or radially of the blank. For a tangential feed a cam 57 mounted on a shaft 59 driven from the gear 41 acts through a lever 53 and circular rack 56 to impart a slow axial feed to the cutter to a position wherein the cutting edges lie in the same plane as the work axis. For a radial feed the shaft 59 is fitted with a cam 69, Fig. 12, operating a rack 68 which may be coupled to the cutter saddle 26. The saddle may be moved relatively to the cam for adapting the machine to different sizes of work by means of a pinion 71 on a shaft which is rotated by a pinion engaging a head 72 which may be locked to the rack by a bolt 77. The rack is constantly urged against the cam by a weight 79 connected to a pinion engaging a rack 84 secured to the saddle. The same means for adjusting the saddle to the work may be used in conjunction with the tangential feed, the rack 68 being in this case secured to the machine bed. A lever mechanism similar to the mechanism 53 may also be used in conjunction with the radial feed modification for the purpose of adjusting the cutter to the axial plane of the work. Downward movement of the spindle is limited by a nut 87 and a spring 85 returns the cutter when permitted by the cam. A guide block 89 on the cutter spindle has helical guide surfaces of the same angle as the cutter teeth and coacts with a complementary guide in the interior of the worm wheel 52. The additional rotation of the cutter to compensate for the thinning of the teeth by repeated sharpenings is effected alternately in opposite directions by moving the driving worm 51 endwise. For this purpose the shaft 45 carries a pinion 92, Fig. 8, driving a vertical shaft 94 carrying a cam 95 acting on the worm spindle 50 through a roller. The cam has high and low dwells, the difference in height corresponding to the maximum compensation required, the actual travel imparted to the worm being limited by a stop screw 102 according to the state of wear of the cutter. The cam drive is so arranged that each dwell is effective while the work rotates through rather more than one revolution and the cutter acts alternately on opposite sides of its teeth.