Patent GB-626854-A (GB)
Title: Improvements in gear grinding machines
IPC: B23F9/02
Filed: 1946-03-21
Abstract: 626,854. Truing grinding-wheels. GLEASON WORKS. March 21, 1946, No. 8832. Convention date, April 24, 1945. [Class 60] [Also in Group XXII] In a machine for form-grinding curved tooth gears, such as spiral bevel and hypoid gears, by means of a cup-shaped grinding-wheel which is fed into the work and swung in an arcuate path for shaping of each tooth space whilst the work remains stationary, the work being indexed between each in-feed of the wheel, the means for feeding the wheel is automatically shiftable after one rotation of the work so that the tooth spaces may be deepened during the next rotation and the number of such cutting cycles is predetermined so that the machine will stop when the teeth have been cut to full depth. Means are also provided for automatically dressing the wheel at predetermined intervals between each grinding cycle, the final dressing being for a finishing cut. Cutter support.-The cutter spindle 95, Fig. 4 is journalled in a head 108 carried eccentrically on a hollow spindle 96 which is journalled in the column 31. An electric motor 100, Fig. 25, drives a pulley 103 connected to a shaft 104 passing through spindle 96 and driving the cutter through bevel gearing 107. The spindle 96 is oscillated during grinding to swing the cutter to and fro across the face of the work to cut the teeth along their whole length, and this movement is effected by an electric motor 110, Fig. 25, driving an adjustable crank disc 124 through gearing 114, 117, 120. A coupling rod 128 transmits motion from the crank to the shaft 131 of a differential gear 132 whose casing is held stationary during grinding of the work so that the oscillations of shaft 131 are transmitted directly through gearing 141 to a toothed segment 142 on the spindle 96. During dressing of the cutter the motor 110 is stopped and the casing 132 is rotated by a gear segment 157 and a fluid pressure operated rack 156 to swing the cutter from the operating to the dressing position. Cutter feed.-A number of cams 181-187 is secured to a shaft 180, Figs. 4 and 25, driven by change gearing 196 and gearing 203, 208 from the motor driven shaft 118, the shaft 180 being moved axially after each rotation of the work to bring a different cam into operation for feeding the cutter deeper into the work during the next rotation. Each cam is of the same shape shown in Fig. 4 providing a slow feed, a dwell for cleaning up the cut and a rapid withdrawal, and is located in turn opposite a lever 211 pivoted in the column 31. A yoked upper end of the lever engages the face of a gear 215, Figs. 4 and 5, secured to a screwed shaft 214 locked to a member 220 by nuts 217, 218 which take up backlash. The member 220 is slidably keyed at 224 to the column 31 and is rotatably secured to the spindle 96 by a nut 222. The operative cam thus feeds the cutter into the work through lever 211 which is urged against the cam and withdrawn by a spring 230 abutting on a flange 232 secured to column 31 and acting on the shaft 214, a link 275 and adjustable nut 279 limiting the withdrawal movement. Wheel dressing. - The cutter dressing mechanism, which may be similar to that described in Specification 576,261, comprises two diamonds carried by swinging arms 440, 441, Fig. 2, for dressing the side faces of the cupshaped cutter W and a third diamond on a swinging arm 443 for dressing the tip of the cutter. The swinging arms are carried by a bracket 444 which is pivoted about an axis 445 on the column 31 to bring them into operative position. The side dressers operate on both the forward and return swings but a bracket 446 for mounting the top dresser is swung aside to remove the tip dresser on the return stroke, and the dressing cycles are controlled by an electric motor 390 which drives a shaft carrying cams which operate valves and solenoids to initiate the successive steps of the cycle. Operation.-In order to pre-set the machine according to the number of successive grinding cycles which are to be performed on the work, the axial starting position of the feed cams 181 &c., Fig. 7, is determined by adjusting a gauge 581 in the machine frame so as to engage a stop pin 583 nn a cylinder 194 which carries the cam shaft, thus selecting which of the cams will be the first to engage the lever 211, the remaining cams being later brought into alignment with the lever in turn. Selector switches 355-360, Fig. 2, arc then set to determine whether, after a grinding cycle, the machine will proceed immediately to the next cycle, with deeper feed, or whether the cutter will first be dressed, and if so, whether the dressing will be a roughing or a finishing operation. The work head is adjusted laterally and angularly to determine the hand of spiral to be produced, and is adjusted vertically to determine the angle of the spiral. The wheel drive motor 100, a motor 352 for driving the work indexing mechanism, (not described), and a motor 509, Fig. 26, for driving a hydraulic pump 510 are started, and the operator then actuates a valve 512 to admit fluid to a cylinder 79 in the work head for operating a draw bar 84 to grip the work in the chuck. Fluid is simultaneously admitted to a cylinder 81 which feeds the saddle 35 to working position, but on reaching this the traversing plunger 87 engages a limit switch 89 to start the dressing motor 390, thus rotating its cam shaft and switching out a solenoid 524 to actuate a valve 521 and reverse the cylinder 81. The saddle 35 is thereby retracted and limit switch 89 is opened, stopping motor 390, but on reaching withdrawn position a switch 90 is closed to restart motor 390 and cause one of its cams to actuate a valve 431. This admits fluid to a piston 150 which carries a rack 156 engaging the toothed segment 157, Fig. 25, of the differential gear housing and swings the cutter W to dressing position. Fluid is simultaneously admitted to a plunger 240 which acts, through a ratchet and adjustable shroud 246, to rotate the shaft 214 and move the spindle 96 axially, thus advancing the cutter to compensate for previous wear. In addition fluid is admitted to a rotary piston 450 which swings the dressing bracket 444 into dressing position, and limit switches operated by the pistons 150, 450 stop the motor 390 as soon as they move. Further limit switches operated by the cutter head and dressing bracket are actuated when these come to operative position to restart motor 390 and cause a further cam to move a valve 430. This admits fluid to plungers 460, 470 carrying racks engaging pinions on the dresser arms 440, 441, 443 which are thereby swung to dress the sides and tip of the cutter. The motor 390 is again stopped by limit switches when the arms start to swing and is restarted at the end of the swing, causing the cam to release valve 430 whereby plungers 460, 470 are actuated to return the dressing arms, and during the return, pressure is released from a plunger 473 so that a spring 476 may swing the bracket 446 about its pivot 478 to remove the tip dresser from the cutter during the return stroke. The side dressers remain in contact with the cutter during the return, which is effected at a slower speed due to exhaust from the plunger 460 proceeding by one of the adjustable throttle valves 500, 501. These valves are at different settings for either rough or finish dressing and the one which is in use for any dressing operation is determined by a selector valve 502 controlled by a solenoid 505 actuated by one of the series of switches 355-360. The motor 390 is stopped during the return by switches on the dresser arms so that it will remain at rest for a period independent of the duration of the return, but these switches re-start the motor when the return is complete. The cam which operates valve 431 then rides off and this valve reverses rotary piston 450 to return the dressing bracket 444 to inoperative position, return the spindle 96 and cutter head oscillating position and reset the plunger 240 ready for another advance of the cutter. The motor 390 is stopped during these movements but is restarted by a limit switch on piston 150 when the cutter head is in operative position, causing a cam to operate a switch to energise a solenoid 524 and operate valve 520. This admits fluid to cylinder 81 to advance the saddle 35 to operative position, the opening of switch 90 stopping motor 390 and the closing of switch 89 starting it again to cause another cam to operate switches to start the feed motor 110 and then to stop itself. The motor 110 starts the spindle 96 and cutter head ascillating through the differential gear 132, rotates the cam shaft 180 and also rotates cams 320, 328, 347 through gearing 341. Cam 320 trips a switch to cause the work to be indexed, taking up backlash in the indexing train, and the cam on shaft 180 which is opposite lever 211 feeds the rotating and oscillating cutter into the work. On withdrawal of the cutter, cam 320 again indexes the work and the feeds, withdrawals and indexing proceed until all the teeth of the work have been operated upon, at which point the cam 347, which actuates a stop mechanism 350, Fig. 2, at each revolution, will have advanced the stop bar enough to operate a switch for energising a solenoid 565 for actuating a valve 556 to admit fluid to a cylinder 286 whose plunger 285 is connected to a slide 291, Fig. 7, carrying a pivoted pawl 297. On the first movement of the slide 291 a cam slot 315 therein lifts a locking plunger 305 from engagement with the teeth of a rack 299 on the cylinder 194 which carries the cam shaft 180, and subsequent movement causes the pawl 297 to engage the rack and advance the cylinder 194 and the cams 181 &c. to bring the cam for the next grinding cycle opposite the lever 211. If the appropriate switch 355 &c. has been set to "grind " position, a circuit will be established by a stop on the cylinder 194 engaging one of a series of stationary switches to cause the feed motor