Patent GB-655895-A (GB)
Title: Method and apparatus for crown shaving gears
IPC: B23F19/00
Filed: 1948-06-21
Abstract: 655,895. Gear grinding. NATIONAL BROACH & MACHINE CO. June 21, 1948, No. 16633. Convention date. July 21, 1947. [Class 60] [Also in Group XXII] In a method of crown finishing gears, a gear W and a gear-like tool T are rotated in mesh at crossed axes, are relatively traversed in a direction which occupies a plane parallel to the normal position of the gear and tool axes, and is angularly related to these axes and either the gear or tool are rocked about an axis parallel to said plane and perpendicular to the gear axis. The tool T may be a shaving cutter or may be a lap, in which case abrasive is applied between the teeth of the lap and of the gear. The angle between the direction of relative traverse and the gear and tool axes may be less than 60 degrees and the rotational speed of the gear and tool may be between 200 and 1,000 surface feet per minute and the traverse between two and ten inches per minute. An overhanging part 11 of the frame 10 carries an angularlyadjustable head 12 for the tool T and a vertically-adjustable knee 21 carries the work W mounted between stocks 35, 36 on a table 26 which is mounted for rocking movement about a pivot 27 on a main table 25. The main table is angularly-adjustable by bolts 49, Fig. 3, and T-slot on an intermediate table 33 which can be traversed on ways 32 on an angularlyadjustable lower table 30; the orientation of the table 26, during adjustment of the tables 30 and 33 as a unit to set the angle of traverse, is preserved by linkage 50. Traverse of the intermediate table 33 is effected by a nut 45 and lead screw 46, the latter being driven by a bevel gearing 47 from a vertical shaft coinciding with the axis on which the lower table 30 is adjustable. A cam device 40 is provided for rocking the table 26 in timed relation to the traverse and comprises a deep cam slot 66 in a block 64 carried by a disc 60 attached to the knee and angularly-adjustable so that the amount of crowning movement can be adjusted and also a flat cam follower 81 universally pivoted in a disc 71 attached to the underside of the table 26. The discs 60 and 71 are adjustable about a vertical axis so that the slot 66 may be set to extend parallel to the direction of traverse. When the rocking movement is not required the table 26 may be rigidly supported by screws 51 in an inclined position if slightly tapered gears are to be produced. In the modification shown in Fig. 5 a greater or more rapid crowning movement, irrespective of the length of traverse movement, is obtained by rotating a lead screw 116 by a telescopic and angularlyadjustable drive 110 connected to changespeed gears 101 in the drive for the traverse feed screw. The lead screw 116 is engaged with a nut 131 carrying an adjustable cam slot 122 which is engaged by table 126. In the modification shown in a follower 121 on a depending arm of the Fig. 8, the drive for the cam lead screw 209 is taken from a bevel gear 202 carried by the traverse feed screw 203. Locking pins 217 and a screw 218 are provided for locking together the tables 225 and 226. In the embodiments so far described, the cam slot is straight but a cam slot 276 having reversely curved ends as shown in Fig. 9 may be provided so that the gear and tool are in loose mesh at the ends of the stroke, in order that the gear may more easily be unloaded, and are brought rapidly into and out of the limiting crowning position by the curved portions 277. In this case, a round cam follower 278 is used. The reverse curve may be provided only at one end of the slot. In the modification shown in Fig. 13, where the traverse of the table 325 is limited to the direction of the arrow 301, a block 310 pivoted on a table 346 angularly-adjustable on the table 325 is rocked by linkage 313 during the traverse and acts on a pair of spring-loaded plungers 341 which have cam slopes acting on depending parts of the rocking table 326. To provide initial adjustment, according to the angular setting of the table 346 and so that, in the mid-position of traverse, the link 313 is perpendicular to the direction of traverse, the link 313 has a slotted opening which receives a pin 316 adjustable along a slotted member 317 on the main table 25 and is connected to the block 310 by bolts 314 engaged in elongated slots in the block. By suitable contouring of the cam slopes of the plungers 341, rocking motion as imparted by the cam shown in Fig. 9 can be imparted. In the modification shown in Figs. 17 and 18, a link 378 acts on a block 377 pivoted on a support 375 carried by an angularly-adjustable table 366 and, through a pair of links 385, the rocking movement is transferred to a second block 382 pivoted at 383. A slot 387 in the block 382 is engaged by a pin 388 on a longitudinally-movable bar 390 having cam elements 391 which are engaged by rollers 392 on the table 360 so that the table is given a rocking motion. A bar 372, longitudinally adjustable relative to the knee of the machine and having several pin-receiving holes 374 and bolts 380 in elongated slots 378, provides for initial adjustment of the linkage.