Patent GB-215402-A (GB)
Title: Improvements in mechanism for cutting the teeth of gear wheels
IPC: B23F5/12
Filed: 1923-09-14
Abstract: 215,402. Greenwood, E. P., and Green wood, E. Sept. 14, 1923. Gear - cutting; attachments for shaping.- Spur and bevel gears and racks are cut from templet cams by means of mechanism which may be attached to the ram of an ordinary shaping machine and which comprises a cutter-carrying bracket-slide carried on the front of the ram and provided with means for giving both the depth feed and tooth profile forming movements to the cutters. while the work is mounted on a dividing-head on the table. In the case of bevel gears further means are provided for progressively modifying the cutter travel so that the cutters always move towards the blank cone apex and for imparting the correct taper to the tooth flanks. In Figs. 1 and 2 a bracket 1 secured to the front of the ram 4 is provided with a slide 5 normally held in its raised position by a spring. Two cutters 40 and 40<1> are - carried in levers 37, 38 pivoted at 39 and having rollers 37<1>, 38<1> engaging a cam 362 which is rotated step by step through ratchet gearing 35 operated from an oscillating wheel 31. The depth of cut feed is produced by a second cam surface 35' and the tooth profile is determined by the form of the cam 36<2>. In a modification for cutting bevel gears the cam 36<2>, in addition to its step by step movement for the depth feed and tooth forming movements, has an oscillating movement for producing the taper of the teeth. In a further modification (Figs. 4 and 6) suitable for cutting bevel gears the wheel 31 which is oscillated through change gearing operated by the engagement of a toothed quadrant on the ram with a fixed rack carries a cam 41 engaged by rollers 46 whose movement is transmitted through tooth formers 48<1> and levers to the tool-carrying levers 37, 38. The lever mechanism is adjustable as shown so that teeth of different sizes may be cut from the same cams. The tooth formers are operated by means of feed cams 52 having intermittent feed operated through gearing from the ratchet-driven wheel 36. The cam 41 which may be of taper form has an inclined slot engaging a fixed pin 66 so that as the cam oscillates a vertical reciprocation of the cam is produced, this movement serving to give the required converging path to the cutters. During the oscillations of the cam 41 a roller 58 connected thereto engages inclined tracks on a cam 57 and thereby forces the cam together with the tool carriers downwardly. As the step by step feed of the cam 57 is effected the roller 58 rides up a helical track 57<1> on the cam to give the depth of cut feed and the inclination of the inclined tracks gradually alters until when the full depth is attained the corresponding cam track and consequently the movement of the cutters during the stroke are horizontal. In this way the direction of the cut is progressively altered so that the tools always reciprocate towards the cone apex of the blank, the latter being so set that a plane tangential to the root cone is horizontal. The vertical movements of the cam 57 are transmitted to the tools through further proportional lever mechanism 61 so that different tooth depths may be cut from the same cam. Fig. 6 shows a cam 41 having three pairs of faces designed to give different amounts of angular movement to the levers 47. For cutting spur gears or racks the cam tracks are all arranged horizontally. A modification of the stepped cam arrangement is described. In a further modification, Fig. 9, a rack 70 reciprocated from the ram carries a slide 71 provided with pivoted levers 72 bearing on an expanding block 73 also. carried by the slide. The levers 72 are connected through further levers 76, 77 to blocks- 79 which are slidable on a bar 80 and which carryformers 79<1> coacting through a proportioning device with the tool levers 37, 38. A loose pinion 81 engages the rack 70 and a horizontal rack 83, the latter being connected to a floating guide 86, whose ends are actuated by cams 88, 92, through a proportioning device. The inclination of thereciprocating slide 85 is thus progressively altered so that varying vertical movements are imparted to the tools through the lever mechanism shown and thus as the depth feed is applied the line of cut is always directed to the blank cone apex. A cam 105 is connected through adjustable lever mechanism to the wedge 74 which is thus gradually lifted so that the outward movements given to the blocks 79 are altered to vary the side angles of the tooth being cut. The bar 80 carrying the blocks 79 is also fed gradually downwards by a cam to enable the former 79<1> to shape the teeth. Modified means for actuating the floating guide are described. The arrangements wherein two cutters are carried on pivoted levers. may be adapted for roughing out blanks, each cutter being caused to rough out its own gap while the means for giving taper to the teeth are rendered inoperative. In Figs. 13 and 14, the oscillating wheel 31 carrying the cam 41 is connected through change gearing with a wheel 140 on a shaft 34 which carries at its lower end a slide 144 having a screw-actuated block 146 engaging by a stud 147 with a block in a quadrant arm 150. A star wheel 151 on the screw 145 is actuated at each reversal of the shaft 34 to feed the block 148 gradually inwards so that the swing imparted to the quadrant gradually decreases to zero, at which point the block is returned by a spring device. A projection 160 on the oscillating cam 41 is arranged to actuate a cam 159 which imparts vertical movement to a block 158 engaging an outer track on the quadrant 150 which is thus moved downwards. A cam track 164 on the underside of the quadrant engages a roller 165 connected as above described to the tool levers and the angular inclination of the cutter path is modified in the required manner through the gradual shortening of the swing of the quadrant 150. Various modifications of this arrangement are described. In a further modification Fig. 23 a cam block 173 coacts with a cam block 175 driven by a shaft 177 which has an oscillating movement combined with a step-by-step feed. An extension 178 on the cam 175 has a surface 178<1> which transmits vertical movement to the cutters. The step-by-step motion of the shaft 177 produces the depth of cut feed while the oscillatory movement causes a gradual feed downwards at a varying rate during the stroke to modify the angularity of the cutter path. Specifications 181,437 and 197,526 are referred to.