Patent GB-489329-A (GB)
Title: Method of and apparatus for cutting gears
IPC: B23F9/10
Filed: 1938-03-09
Abstract: 489,329. Gear cutting. GLEASON WORKS. March 9, 1938, No. 7363. Convention date, March 10, 1937. [Class 83 (iii)] In a machine for cutting curved-tooth bevel or hypoid gears a pair of face-milling cutters are arranged to operate simultaneously on different tooth spaces of the blank P which is indexed periodically through a number of tooth spaces so that the tools first cut slots of uniform width in the blank and then each tool operates on a space previously cut by the-other tool to produce a tooth space which tapers from end to end. The invention may be applied either to form cutting or generating and the embodiment described is a generating machine similar to that described in Specification 467,769. The cutting mechanism is mounted in a cradle which is oscillated in timed relation with the rotation of work-spindle 1120, Fig. 21. The cradle is operated from a hydraulic piston 1170, Fig. 20, through a gear train including the rack 1181, gear 1215, and bevel gear 1224 and the work-spindle is driven in unison with the cradle through the train 1195, Fig. 20. The feed and withdrawal movements of the work are effected from a cylinder 1350, Fig. 21, through the link 1360 and the valve mechanism controlling the machine cycle is similar to that described in Specification 467,769. The cutting mechanism comprises a pair of eccentrically-mounted cutters C, C<1>. The inner cutter C has blades 31 on a head 30, the centre lines 33 of the cutting portions being inclined to the median lines 32 of the body portions, Fig. 16, and extending parallel to the head axis. The blades are seated on the conical upper face of a ring 39 and secured by bolts 37. The outer cutter C<1> consists of a ring-shaped head 40 having cutters 41 similar to the cutters 31 secured to slots in the inner surface of the ring. Some of the blades may be for bottom cutting and others for side cutting or all may be side cutters of which different blades may cut on opposite sides or all may cut on both sides. The inner cutter is mounted on a spindle 52 and the outer cutter is bolted to a plate 61 and locked against rotation thereon by spring plungers 67. The plate 61 has a radial slot engaged by a roller or a pin secured to a driving plate 85 on a sleeve 53 surrounding the spindle 52. An internal gear 1100 drives both cutters and is driven from a shaft 1095 and a gear train similar to that described in the abovementioned Specification. The carrier 60 for the cutter mechanism is eccentrically mounted in the cradle 100 and is adjusted according to the spiral angle of the work from a stub-shaft 1110. The distance between the cutters C, C<1> at the point of cut is adjusted from a shaft 115 which rotates a ring 76 in which the drive plate 61 is eccentrically mounted on rollers 75. As the ring 76 is rotated it shifts the plate 61 laterally and rotates the cutter C<1> angularly about the cutter C to vary the distance between the cutters at any given point without changing the distance between the cutter axes. Rings 125, 126 are secured to plate 61 and a disc 127 respectively to exclude chips and a protecting hood 130 is also provided. The cutters are adjusted together to compensate for wear by rack-and-pinion gearing actuating the sleeve 58 which is secured after adjustment by clamping blocks, and the cutter spindle 52 is independently adjustable axially by means of a threaded central rod 145. The index mechanism includes a pivoted double-armed lever 187 carrying a locking-dog 190 engaging notches in an index plate fast with the work-spindle, the dog being urged against the plate by a spring plunger 198 engaging a roller 199. A pawl 206 carrying a roller 213 is spring-pressed against a ratchet ring 195 to lock the work-spindle when the dog is disengaged. When the locking-dog is engaged a cam surface on lever 187 engages the roller and lifts the pawl away from its ratchet wheel. A cam plate 215 secured to the work head coacts with pivoted trip dogs 220, 221, and a bushing secured to the lever 187 carries star wheels 232, 233 carrying pins engageable with the dog 220 to hold this dog out of engagement. The star wheels are advanced at each oscillation of lever arm 187 by a pawl 238. The cam surface 218 of the cam plate acts on the dog 221 for only a short travel so that the locking dog is quickly released to drop into the next notch, but the cam surface 217 coacting with dog 220 is of sufficient length to keep the dog in its raised position for a rotary movement greater than the distance between the notches. During rotation in the clockwise direction the work-spindle moves with the lever 187 until the locking-dog is disengaged by the trip dogs 220, 221. The pawl 206 will then be engaged as in Fig. 8 to hold the work-spindle stationary while the lever 187 and other associated parts continue the movement through two notches until the dog 220 leaves its cam surface. The trip dogs are ineffective on the counterclockwise movement during which the generating roll takes place. At each clockwise movement (return roll) the star wheels 232, 233 are fed by one step until they reach a position wherein the dog 220 is held out of engagement. When this occurs the locking-dog is only held up by the short cam surface 218 coacting with dog 221 so that the next indexing occurs through only one notch. On the next succeeding movement the star wheels are moved another step, thus releasing the dog 220 so that indexing again occurs through a distance of two notches. By suitable positioning of the star wheels and pins, the single space indexing may be made to occur one or more times at any point or points in the operation. If only double space indexing is required, as in cutting wheels with an odd number of teeth, the star wheels are removed. The cycle of cuts in generating an even number of teeth is shown in Fig. 19. The two cutters first cut the spaces 310, 317, leaving a finished tapering tooth 300. After indexing through two teeth the spaces 311, 312 are cut, then the spaces 313, 314, and then spaces 315, 316. The blank is now, as described above, indexed through only one tooth so that each cutter operates in a space previously slotted out by the other cutter; the shaded areas adjacent the lines 337, 340 are removed thus producing the required taper of the spaces. The double indexing is now resumed and the metal shown by the cross-hatched areas adjacent the teeth 301, 303 and 305 is removed in successive operations, the gear being then finished. The procedure for odd numbered wheels is similar, but in this case double indexing is employed throughout. Since the second cuts are lighter than the first or slotting cuts, the operation may be speeded up during the former operation. For this purpose the throttle valve 1260, which is automatically controlled by the cam 1300 to vary the speed at different parts of the generating cycle, has additional means for increasing the valve opening after all the tooth spaces have been slotted out. At each reversal of the rolling, the valve 1266 operates a piston 350 to actuate rack-and-sector and ratchet mechanism 361 to impart step-by-step movement to cam plates 371, 372, the initial position of which depends on the number of teeth to be cut. The cams actuate a roller operating an arm 393 coacting with the lever 1316 controlling the throttle opening. At the beginning of the operation, the roller is on the low part of the cams and the throttle is controlled by cam 1300. When the slotting is completed the rollers reach the high part of the cams and the lever 393 is actuated to open the throttle valve fully. The cams may be relatively angularly adjusted so that the length of the high part may be regulated. The stops 1385 and 1395 controlling the valve gear operate in a way similar to that described in the above-mentioned Specification. The complete withdrawal of the blank to loading position on completion of the operation is actuated from the speed-up mechanism. A cam 373 on the cam-shaft 364, Fig. 14, has a projection 400 which is timed to engage at the end of the operation with a lever 401 actuating a spring-urged valve 405 controlling a cylinder 410, Fig. 21, which acts through lever mechanism on the bell-crank 1508. When this member is rocked, the stop 1385 is withdrawn and complete withdrawal of the work to a loading position is effected. The rate of feed and withdrawal movements of the work are controlled as described in the prior Specification mentioned by a throttle valve 1475.