Patent GB-222732-A (GB)
Title: Improvements in mechanism for cutting the teeth of gear wheels and racks
IPC: B23F5/12
Filed: 1924-01-11
Abstract: 222,732. Greenwood, E. P., and Greenwood, E. Jan. 11, 1924. Gear-cutting. - In a machine for cutting the teeth of gears or racks the cutter or cutters are carried by members which are canted alternately in opposite directions while the tools are gradually fed to depth. The cutter head is adapted to be attached as a unit to the ram of a shaping machine but alternatively the head may form part of a complete gear-cutting machine. In Figs. 1 and 2 a main casting 1 secured to the front of the ram 4 carries a slide 5 normally pressed upwardly by a spring 6. The member 1 carries shafts 7, 8 connected by change gearing. The shaft 7 is operated by a ratchet wheel and drives an escapement wheel 12 through. skew gears 10, 11, while the shaft 8 drives through similar gearing a cam 16 on a shaft 15. The pivoted cutter-box 21 is carried on a canting-plate 17 which engages the slide 5 through a curved tongue 17<1 >whose centre is located on the pitch line of the tool 22. The plate is canted alternately to opposite sides by means of a pivoted forked lever 19 having pins engaging as shown with the escapement wheel 12 and provided with a central stem engaging rollers 18 on the canting- plate. In operation, the canting movement causes the prongs of the cutter to act as stocking- tools while a.t the same time depth feed is imparted by means of the cam 16 engaging a roller on the slide 5. As the. depth feed is applied the rollers 18 gradually approach the pivot centre of the lever 19 so that when full depth is attained the canting motion ceases and the tooth is finished to the form of the cutter space. The stem of the lever 19 may be cam-shaped to vary the form of tooth produced. Modified means are described for imparting the canting movement to the plate 17. In one modification, Fig. 8, the canting- plate is provided with arms having series of holes adapted to receive rollers bearing on levers 29 and 30 having rollers engaging cams 25<2>, 26<2>. The amount of canting movement may thus be varied according to the requirements of the gear being cut but the cant does not diminish to zero when full tooth depth is attained. In another modification, Fig. 10, the slide 5 is fed by a depth cam 16 and carries two canting cutterplates, which are provided with bosses forming bearings for adjustable quadrant plates 34, 35 slotted to receive blocks carried on a slide 39. This slide is actuated by a rocking lever 40 which is so timed that on the cutting stroke the toe of the lever engages the slide 39 while on the return stroke the lever allows the slide 39 to move upwardly to withdraw the cutters from the work. In addition to this canting movement to relieve the cutters, the angular positions of the cutterplates are progressively altered by the action of the depth-feeding cam 16. In Fig. 12, which shows a modification for cutting double helical wheels, two canting heads C, C<1> are carried on rams 56, 57 which are alternately reciprocated over the blank 58. The rams are operated from a worm 44 through shaft 46 and bevel gearing, crank-discs 50, 51, and slotted members 54, 55 attached to the respective rams, these members being adjustable on the rams to ensure that the tools each cut to the centre of the blank. The blank is continuously rotated synchronously with the rams by the gears 59, 60, crank pin 62, rack 64, reversing bevel gearing 69, bevel gears 70, shaft 73, change gears 74, and worm gearing 78. The reversing bevel gearing is operated automatically at the ends of the ram travel so that the motion of the blank is uni-directional. The front of the bed carries a slide 81 so that the blank arbor and associated parts may be adjusted according to the size of the blank. In order to withdraw the tools on the return strokes the slide 5 of each canting head is provided with an extra slide 82, Fig. 15, which carries the cutter-plates and has rollers 83 engaging a cam surface on a lever 84 which is automatically operated through a dog 86 to withdraw the cam surface and allow the cutter slide to be raised for the return stroke. In a modification for double helical gears, the rams work in slides which are adjustable in arcuate guides to facilitate, the cutting of teeth of different angles. Figs. 17 and 18 show a modification suitable for cutting hollow-faced wormwheels, a frame 103 having a circular slide 103', top bearing 103<3> and trunnion 103<4> in alignment with a lower bearing 103<2>. A driving shaft 104 drives through bevel gears 105 and change gears 109, two vertical shafts 111, 112 carrying skew gears engaging a gear 115 on the cutter spindle, the latter being carried in a bracket 120 having bearings 121 on the slide 103<1>. The bracket 120 and the cutter spindle with its driving gear are rotatable about the axis of the shaft 107 and may be canted about the axis of the driving shaft 104. The latter shaft carries cams 122, 123 actuating an escapement lever 124 which is adjustably connected to the bracket 120 to oscillate the cutterspindle. The other side of the escapement lever is adjustably connected to an extension of the frame 103 so that canting movement is given to the cutter simultaneously with its swinging movement about a vertical axis. The blank is fed towards the cutter to give. the required tooth depth. Tools.-Various. shapes of stocking-tool may be employed or one or more sets of stocking-cutters may be arranged in front of a finishing cutter to divide up the cut. Separate single cutters may also be employed to shape opposite sides of a tooth. For cutting worm wheels the cutter may be of rack form or a wide cutter passing transversely through the cutter-spindle and arranged to cut at both sides may be used.