Patent GB-1067807-A (GB)
Title: Improvements in or relating to lapping machines
IPC: B24B37/04
Filed: 1965-11-23
Abstract: 1,067,807. Lapping. SPEEDLAP CORPORATION. Nov. 23, 1965 [Dec. 8, 1964], No. 49693/65. Heading B3D. A lapping machine comprises a framework, a lapping disc mounted on the framework for rotation about a vertical axis, a contour control member having a maximum horizontal dimension substantially less than the radius of the lapping disc, and means secured to the framework and arranged to position said contour control member so that the lower surface thereof engages the lapping surface of the lapping disc. Workpieces are positioned within truing and retaining rings 30 below pressure plates secured to the lower ends of piston rods 28 of pneumatic jacks 24 mounted at the outer ends of transverse arms 22 provided on a bridge 20 extending between the upper ends of columns 18. The rings 30 slightly overlap the inner and outer peripheries of the annular lapping surface of the lapping disc 14, to which a mixture of abrasive particles and oil is fed. The inner annular portion of the lapping surface wears more rapidly than the outer annular portion; to correct this, contour control devices 32 are provided. Each device includes a bracket 34 extending from a column 18 and mounting a pneumatic jack 38. The piston rod 40 of the jack has threaded into its lower end a bolt 42, Fig. 2 (not shown). Secured between the end of the rod and the head of the bolt are a casing 44, a bushing 46 and a split collar 48 having a conical lower face. Engagement of this face by the head of the bolt expands the collar into tight contact with the inner face of a self-aligning ball thrust bearing 50. The outer annular aligning sleeve of the bearing is received in a recess defined by a clamp ring 52 and a spacer 54. Bolts 56 extending through the ring and spacer are threaded at their lower ends into a holder 58. The lower face of the holder has a central circular recess 60 and an annular recess 62 in which is secured, e.g. by epoxy cement, a wear ring 64 of material having greater abrasion resistance than the material of the lapping disc, e.g. boron carbide. An opening 66 in the holder 58 permits insertion of a screwdriver to turn the screw 42. The holder 58 and wear ring 64 constitute a contour control member 68. Each member 68 has a diameter substantially less than the radial width of the annular lapping surface of the disc 14 and substantially less than the diameter of the rings 30. The radial distance between the axis of rotation of the disc 14 and the axis of rotation of a member 68 is greater than the radial distance between the axis of rotation of the disc 14 and the axis of rotation of a ring 30. The members 68 slightly overlap the outer periphery of the disc 14. When correction is necessary, the jacks 38 are actuated to lower the members 68 into engagement with the disc 14, preferably with a constant pressure of 10 1b. p.s.i. When the lapping surface of the disc has been restored to a planar condition, the members 68 are raised. Alternatively, to accommodate variations in the rate of wear of different portions of the lapping surface of the lapping disc, the contour control member may be continuously urged into engagement with the lapping surface with the pressure being varied as required.