Patent GB-808250-A (GB)
Title: Method and apparatus for grinding worm elements
IPC: B23F13/08
Filed: 1957-03-08
Abstract: 808,250. Grinding worms. MICHIGAN TOOL CO. March 8, 1957 [May 29, 1956], No. 7837/57. Class 60. A method of grinding the thread of a worm element 20, Fig. 1, of the double-enveloping type comprises a grinding wheel 98 which has its grinding surface in contact with the rotating element for the entire depth of the thread and is angularly moved about an axis perpendicular to the axis of rotation of the element as, simultaneously, its axis of rotation is tilted as a function of the varying helix angle of the thread. The worm element 20, which is mounted between a headstock 22 and tailstock 24, is rotated in timed relationship with the angular movement of a table 14, on which is mounted the grinding wheel 98, as described in Specification 594,824. The grinding wheel is driven by a belt 134, Fig. 2, from a motor 128 and is mounted on a housing 92 which may be angularly adjusted about the axis of a spindle 64 to align the grinding wheel to the helix angle at some part of the worm and then clamped by a member 86 to a head portion 80 of the spindle 64, the axis of which is coplanar with the axis of the worm element. The spindle 64, which is mounted in bearings 66, 68 in a support member 28 slidable to and from the worm element on ways 30 on the table 14 by means of a screw 46 and nut 42, is rocked to align the grinding wheel with the variations in the helix angle during the angular movement of the table 14 by an arm 146 which, at one end, is secured to a stud 136 keyed into the spindle 64 and, at the other end, carries a cam follower 150 which co-operates with an arcuate cam 156. The cam is mounted on pins 160 carried by supports 162 which are vertically adjustable, to vary the upper contour of the cam by means of screws 180 and nuts 182, 184, in ways 166 secured to a flange 170 fixed to a machine base. The spindle 64 is returned to its initial position, after rocking by the arm 146, by pins 210, 212 which are spring-urged against a member 216 secured to the spindle. The grinding wheel is mounted between ball bearings on a shaft perpendicular to the axis of the spindle and is provided with felt seals, shields and covers to prevent the entry of dust into the bearings. In a modification, in order to present a reduced contour radius of the grinding surface to the worm without reducing the diameter of the grinding wheel, the grinding wheel shaft is arranged at an angle to the axis of the spindle 64. In a further modification, in order to grind worms having a high helix angle, a smaller diameter grinding wheel is mounted on one end of a shaft arranged at an angle similar to that of the previous embodiment. A convex form may be dressed on the underside of the grinding wheel when it has been tilted to the desired helix angle by a dresser which is clamped in a groove 232, Fig. 1, in a member 226 slidable to and from the grinding wheel on a shelf 224 secured to the flange 170, the table 14 being rotated to present the wheel to the dresser. The dresser, Fig. 6, comprises a base 228, on which a support member 234 is pivotally connected by a post 236, a nut 240 clamping the support member in the desired angular position. A sliding member 246 engages dovetailed ways 244 in the support member 234 and carries a pivoted bar 252. One end of the bar is provided with a recess to receive a projection 258 of a tool holder 256 which carries a diamond or like dressing tool in a bore 266 ; the tool holder may be rotated in the recess and clamped by a screw 262. The other end of the bar is pivotally connected by a stud to a T-nut 294 adjustably secured to a linkage 278 which, in turn, is pivotally connected by a stud 280 adjustably clamped to a slotted plate 272 fixed to the support member 234. The linkage 278, therefore, imparts a rocking movement to the bar 252 as the member 246 is reciprocated in the ways 244, raising and lowering the dressing tool in its back and forth movements to dress a convex surface on the grinding wheel. A straight surface may be dressed on the wheel by slackening the stud 280 so that it is free to move in the slotted plate 272 and clamping the bar 252 to the sliding member 246 by a strap 302 and bolts 304.