Patent GB-467769-A (GB)
Title: Improvements in machines for producing gears
IPC: B23F9/10
Filed: 1936-06-23
Abstract: 467,769. Gear - cutting. TENNANT, W. J. (Gleason Works) June 23, 1936, No. 17482. [Class 83 (iii)] In a gear-generating machine of the intermittent indexing type, both the generating mechanism and the mechanism for producing alternate feed and withdrawal movements between tool and work, are operated by fluid pressure. The machine cycle consists of a depth feed of the work into the cutters, then a generating rolling movement of the cutter and blank, then withdrawal of the work from the cutter then a return roll of the cutter and blank during which the work is indexed in readiness for a fresh cycle. The column 31 houses the usual cradle in which the face-mill cutter T is mounted. A plate 34 longitudinally adjustable on the bed has transverse ways for the screw adjustment of a column 40 having integral upper and lower wings 41, 42, respectively, between which the swivelling work-head 50 carrying the spindle of the blank P is mounted. An overhead tie 730 connects the columns 31 .. 40 to increase the rigidity of the machine. The column 31 has semicylindrical bearings 54, 55 coacting with complementary half bearings in a cap member 57 to support the cradle 56. The cutterspindle 60 is journalled in a sleeve 63 eccentrically mounted in a carrier 64 which is itself eccentrically mounted in the cradle in a bearing 65. Thus by rotating the carrier from a shaft 110 the distance of the cutter axis from the cradle axis may be adjusted, the position being indicated by a graduated retaining ring 107. The cutter is driven from a motor 70 through bevel gearing 71, spur gearing 75, shaft 76 coaxial with the cradle, spur gearing 88, shaft 90 coaxial with the carrier, gears 93 shaft 95 and internal gear 100, the latter being secured to a guard or flywheel 102. This gearing permits the adjustments of the carrier and cradle without the use of telescopic shafts. Means are provided for preventing axial movements of the cradle and carrier. The work-spindle 120, enclosing a tapered arbor 121, is mounted in a front plain bearing 122 and rear ball bearings 123 and carries a ratchet-wheel 125 and index plate 126. A flanged member 130 rotatable on the workspindle carries a hypoid gear 135 engaged by a pinion 210, Fig. 7, to impart the generating motion to the work, when the . member 130 is locked to the spindle. The indexing- mechanism comprises . a double lever 140 pivoted at 138 and carrying a locking dog 144 held in engagement with the index plate by a spring plunger 150 engaging an arm integral with the lever. A pawl 155 is pressed against the ratchet wheel by a plunger 159 and is normally held disengaged by cam surface 161 of the lever. When the lever arm rotates counter-clockwise the trip dog 147 rocks past a trip lug 165 but on the return movement the trip lug causes the lever 140 to be rocked about its pivot to disengage the locking dog and allow the pawl 155 to engage its wheel and hold the work-spindle stationary while the member 130 is further rotated by the hypoid gearing 135 until the locking-dog engages the next index notch and the pawl 155 is disengaged. The indexing occurs during the return generating roll of the work and cutter. The generating movements are both derived from a fluid pressure piston 170, Fig. 27, which reciprocates a pair of racks 180, 181. The rack 180 is connected through gearing to the above mentioned hypoid gear 135 to impart generating movements to the work. The rack 181 is connected to the cradle 56 to impart corresponding generating movement to the cradle. In using a cutter which cuts on opposite sides with alternate teeth, the changing thrusts on the work tend to produce inaccuracy and to avoid this means are provided in the work driving train for taking up backlash always in the same direction. For this purpose a housing 231 secured to the work head carries an arcuate shoe 237 having fluid tight engagement with a sleeve 230. Keyed to this sleeve is a shoe 245 fitting against the housing 231. Oil is admitted to the housing 231 through duct 256 and exhausted through the same duct while a duct 257 carries away leakage past the shoes. During the return roll of the machine the work-spindle rotates counterclockwise and the line 256 is open to pressure which is transmitted to the shoe 245 to take up backlash in the driving train. During cutting, the work spindle rotates clockwise, Fig. 7, escape of oil from in front of the shoe 245 through the duct 256 is controlled by a throttle valve 260, Fig. 26, which again puts a load on the work driving gear and takes up backlash in the same direction as before. In a modification, the hydraulic brake mechanism is effective to take up the backlash in both the work and cradle driving trains. In this form, Fig. 28, the rack 180 is dispensed with and the rack 181 drives a cradle gear 224 which is itself connected through the gearing shown in Fig. 28 to the hypoid gearing 135 operating the generating movement of the work. Thus the braking of shoe 245 is transmitted back to the rack 181 through the whole gearing including both the work and cradle driving trains. The throttle valve 260, Fig. 26, also controls the speed of the piston 170 during the generating roll while reversal is controlled by a second valve 266 supplied from a pump through line 268 and connected to opposite ends of cylinder 170. In one position of the reversing valve, Fig. 26, fluid flows to the right of cylinder 170 and moves the piston to the left while exhaust from the cylinder flows to the throttle valve. The leftward movement of the piston imparts generating movement to the cutter and work spindle and moves the shoe 245, Fig. 26 clockwise to exhaust fluid through a line 255 which joins the exhaust from cylinder 170 passing to the throttle valve which thus serves not only to control the speed of the generating roll but also to apply the above described hydraulic brake to take up backlash. The throttle valve is automatically operated to vary the speed during the generating roll so that approximately constant cutter load is maintained. During the first part of the roll the speed is lower than during the latter part. For this purpose the position of the throttle valve is controlled by a cam 300 driven from the rack 181, Fig. 26 and operating a bell-crank 310 connected to the throttle valve. The first part of the roll is effected at normal speed but about 15‹ from the end of the roll the cam causes the throttle valve to open and increase the speed. The work head is mounted in the wings 41, 42 on trunnions which are coaxial with the hypoid pinion shaft 207 so that the work head may be swung to feed the work to the cutter. This feed is produced by a fluid pressure piston 350, Fig. 26, acting on the work head through a link 360. The depth of feed is determined by a stop rod 370, Fig. 5, adjustably fixed in a stop bar 375 and connected to the work head by a link 371. Withdrawal movement of the work head for indexing is limited by a stop 385 on the stop bar, Fig. 26 coacting with a lug 393 on the column 40. As the stop bar reciprocates with the work head projections on an adjustable plate and on the stop 385 operate a pilot valve 396, Fig. 26, connected to the reversing valve 266 to reverse the roll movements. The reversal of feed piston 350 is controlled by a valve 425, Fig. 26, which in turn is controlled by a pilot valve 426. For this purpose the rack 181 is arranged to oscillate a gear 305, Fig. 26 carrying stops 450, 451 actuating a lever 454 to change over the pilot valve 426. The rate of depth feed is governed by a throttle valve 475. Fig. 26 which gives rapid approach movement and slower cutting feed, the throttle valve being controlled by a lever 490 one arm of which runs on a cam bar carried by the feed stop bar to maintain the throttle valve open for the approach movement and to give progressively slower feed as the blank is fed to depth until a predetermined minimum is reached. The feed throttle valve is not operative during the withdrawal of the work head. The oscillations of the bell-crank 490 as each tooth is cut are used to operate automatic stop mechanism 500 as described in U.S.A. Specification 1,577,121 to stop the machine on completion of the work. On the final feed movement the stop 385 which normally determines the work withdrawal is automatically moved aside so that the work is further withdrawn to a loading position on completion. This is effected by a lever 506 of the stop mechanism which is connected through link 507 to a bell-crank 508 operating the stop member, the withdrawal movement being then limited by the contact of stops 515, 516. Means are provided for maintaining the stop 385 in inoperative position during the whole of the last generating roll and to return it during the return movement of the work head when a fresh blank is chucked. The blank chucking mechanism comprises a collet 535, Fig. 6, engaging over the pinion stem 536 and secured to a draw bar 538 urged by a coil spring 540. A sleeve may be pressed forward to overcome the spring pressure and release the collet by means of a lever 556 actuated by a piston 547 controlled by a valve 485, Fig. 26 which is shifted from a hand lever 575 for chucking. The de-chucking of the work may be effected automatically by means of an arm 580 operated by a plunger 582. During the movement of the work-head to loading position a catch is operated to release the plunger which is then moved downwards by a spring 587 to cause the work to be dechucked. The plunger movement also locks the stop bar and prevents return of the workhead until a fresh blank has been chucked and the valve 485 shifted. A limit switch 605 is opened to stop the cutter by movement of the valve 485 by the automatic mechanism and the cutter cannot be started until the valve has been moved manually to chuck the blank. Another safety device prevents dechucking of the work while it is in the cutting position. After de-chucking, the blank is strip