GB228553A - Improvements in or relating to the generation of gears - Google Patents

Abstract

228,553. Gleason Works, (Assignees of Tribojevich, N.). Jan. 28, 1924, [Convention date]. Gear-cutting; milling- cutters. - Tapered or cylindrical worms of constant pitch are hobbed by means of a cutter in the form of a crown wheel of the modified involute type, that is, having teeth which longitudinally form tangential curves of a common involute of a circle. The blank is arranged tangentially of the crown wheel cutter, and the cutter and blank are rotated in timed relation. For tapered worms the feed is usually perpendicular to the pitch-plane of the cutter, but in the case of cylindrical worms an axial blank - feed is employed. The cutter A, Fig. 1, may be formed in a universal milling machine by means of a rotary end mill G arranged in a line b which is offset from the axis of the cutter bv a distance equal to a + p where a is the base radius and p the modification. The cutter is rotated and moved along the line b, the lead being equal to 2aII. The sides of the convolutions are then bevelled off to the required pressure angle, gashed by means of flutes, b1, b2, b3 - - - and finally relieved. In Fig. 1 the flutes are preferably curved and of abridged involute form. The number of flutes is always relatively prime to the total number of convolutions in the hob. The Specification demonstrates that a hob of the form above described will correctly generate a tapered worm of constant pitch arranged with a generator in the line b, the dimensions of the cutter being given by the equations. where n1 and n2 are the number of threads in the worm and hob respectively, # the pitch cone angle of the hob, and P0 the pitch the generator b. Fig. 3 shows the generation of a multithreaded worm A, from a cutter having a large value of the modification and flutes d3 of abridged involute form. The sections of the worm thread are as shown at B1. In addition to a feed movement, perpendicular to the pitch plane of the cutter, the worm may also be fed slightly lengthwise to avoid the formation of facets on the work. In the manufacture of cylindrical worms, Fig. 9, a spiral of a single convolution having a lead equal to the pitch p0 of the worm to be generated is used, and the diameter of cutter is such that the radius of curvature of the hob spiral is always greater than the corresponding radius of plane sections of the worm thread. The worm is fed axially to complete the generation of the teeth. The slight mutilation of the teeth produced owing to the differences in the hob-thread angles at the beginning and end of the spiral may be minimized by reducing the thickness of the hob-teeth where necessary. In a machine, Figs. 10 and 11, for carrying out the invention, the hob 21 is mounted on a face-plate 23 driven by worm gearing 29, the tool head being adjustable by a screw 33. The work arbor 38 is driven through spur gearing 45 and further gearing, Fig. 10, from the pulley 71. The end of the work spindle is screwed, and to give axial feed of the worm a nut 43 on the spindle may be driven at the required speed through change gears 46. The work-head is angularly adjustable about the axis of the shaft 52 according to the taper of the work. Vertical feed is imparted to the work-head by means of a screw 66 which may be actuated either by hand or by power. The gear train driving the hob-spindle includes change-gearing 82. For cutting crown gears the positions of the work and hob are interchanged, a taper hob being mounted on the arbor 38. Grinding tools may be employed instead of cutters, and these may be dressed by means of a rapidly rotating diamond 85, Fig. 12. mounted eccentrically on a spindle 84, the grinding wheel 83 being rotated slowly on its axis and fed along a line such as b to generate the spiral tooth form. In a modification of the truing device, Fig. 15, the wheel is trued by a small cylindrical wheel 88 which is itself trued by means of a diamond 85.