947,142. Lapping. SPEEDLAP CORPORATION. Oct. 10, 1962, No. 38403/62. Heading B3D. [Also in Division F2] A lapping machine comprises a disc mounted for rotation about a vertical axis and having a horizontal planar lapping surface on its upper face, at least one ring resting on the lapping surface for retaining a workpiece and truing the lapping surface, each ring being normally freely rotatable in one direction about its own axis by frictional contact with the rotating lapping surface, and means for rotating each ring about its axis in the reverse direction to its normal rotation when it is desired to restore the planar condition of the lapping surface. A tubular housing 11, having an access door 14, rests by lugs 12 on a base ring 13. Near its upper end the housing 11 has an inclined partition 15 welded at its periphery to the inner surface of the housing, the partition forming a drip-pan and supporting a collar 16 having an internal flange 17 upon which a gear reducer unit 18 is bolted. The input shaft of the unit 18 is belt-driven by a motor 29 bolted to a plate 26 pivotally carried by the housing 11. The output shaft of the unit 18 has keyed thereto a hub 21 supporting the lap 22 which is a circular wear-resisting metallic alloy disc with a central well 23 and radial slots 25. A mixture of abrasive particles and carrier in a tank 47, having a filling inlet 48, is fed, by a pump driven by a motor 50, through a discharge tube 51 to a spout 52 overhanging the lap surface, to which drip-feed of the mixture is effected. Used mixture gravitates to the drip-pan formed by the partition. The lap 22 is surrounded by a ring 36 on which is mounted a table 37 having opposed notches 38 receiving vertical channel columns 39 mounted on opposite sides of the housing 11. Means are provided for slightly raising or lowering the table 37 relatively to the lap surface to facilitate loading and unloading workpieces to and from the lap. A bridge member 40 mounted between the channel columns 39 above the lap has transverse arms 41, 41 at each end of each of which is a bore receiving a spindle 42. Each spindle has a knurled upper end for manual grasping, is held in vertically adjusted position by a setscrew 43, and has its lower end taking into a ball bearing 44 in the centre of a circular weight plate 45. The four weight plates fit with slight clearance within truing-retainer rings 46. Workpieces W are placed within the rings, face to face on the lap, and the weight plates placed upon them. A horizontal circular friction drum 53 mounted coaxially with the lap and centrally of the group of rings 46 comprises a circular friction member 54, of rubber or the like, and metal top and bottom plates 54<SP>11</SP>, 54<SP>11</SP>. A nut 55 resting on the bottom of the central well 23 of the lap 22 has a tubular boss 56 receiving a threaded stem 57 extending downwardly from a hand knob 58 and threading into the base portion of the lap. The friction member is in frictional contact with the peripheral surfaces of all the rings 46, and the hand knob can be turned to either of two positions, (1) to leave the friction drum face to rotate, idly driven by the rings, or (2) to be rigidly connected with the lap and thus drive the rings 46 in the reverse direction. This reverse drive of the rings, applied at intervals and for brief periods of time, as may be necessary, dresses the lap surface for the maintenance of its planar condition. In a modification, Fig. 5, the truing-retainer rings 46a have their external cylindrical surfaces formed throughout with elongated gear teeth. A stud 59 extends upwardly from the lap 22a. A pinion 62 is mounted on the stud 59 by means of a loosely surrounding sleeve 63 secured on the pinion by a cap screw 64 and having an internal shoulder resting on a shoulder of the stud 59. The reduced upper end of the stud extends with slight clearance into the reduced bore at the upper end of the sleeve. A pin 67 press-fitted in the top of the stud 59 receives a hand-cap 69. Clutch pins 70, 70 press fitted in the under side of the hand-cap 68 extend downwardly for entry into sockets 71, 71 formed half in the reduced upper end of the stud 59 and half in the upper end of the sleeve 63. The hand-cap 68 has limited vertical movement determined by circumferential grooves 72a, 72b and a spring-pressed ball 73. The pins 70, 70 enter the stud halves of the sockets when the hand-cap is in the lower position, locking the pinion 62 to the lap whereupon the rings are driven in reverse direction. When the hand-cap is in the upper position, the pinion is free to rotate, idly driven by the rings rotating in normal direction. Specification 926,751 is referred to.