Patent GB-1087992-A (GB)
Title: Work-holding or dressing attachment for a lapping machine
Inventor: SWAN RICHARD JAMES
IPC: B24B37/10
Filed: 1963-08-15
Abstract: 1,087,992. Lapping. ENGIS Ltd. Aug. 5, 1964 [Aug. 15, 1963], No. 32358/63. Heading B3D. A work-holding or dressing attachment for a lapping machine of the kind which includes a rotary lapping member comprises (i) a rotary member which constitutes a work carrier when the attachment is used for work-holding or a dressing device when the attachment is used for dressing, a surface of which forms a work-supporting or a dressing surface respectively and which is rotatable about a central axis, (ii) means for locating the rotary member above the lapping member and with the said central axis parallel to and offset with respect to, the axis of rotation of the lapping member, and (iii) an idler shaft arranged to be driven from the periphery of the lapping member and to transmit the drive to the rotary member. A lapping disc 11 is rotated by a motor 16. A column 17 is mounted on the machine frame 20. An arm 18 pivoted on the column 17 has fixed thereto a bearing 19 in which is rotatably mounted the upper end of an idler shaft 21; the arm 18 is loaded by a torsion spring within the column 17 to maintain a gear-wheel 22 on the lower end of the shaft 21 in mesh with gearteeth 10 on the periphery of the lapping disc. Rods 24, 24 secured at one end to the arm 18 and at the other end to a block 25 pass through horizontal bores, fitted with phosphor-bronze sleeves 27, in a guide block 26. A rod 31 is a sliding fit in a vertical bore in the block 26 and has at its lower end a part-spherical surface 36 engaging in a part-spherical cavity in a rotary member 33 carrying workpieces 34 on its lower face. The member 33 has a part-spherical side surface 37, this surface and the cavity having a common centre which is also the centre of the surface 36 when it is in position in the cavity. A tension spring 28 is fixed at one end to the block 26 and at the other end to an externally screw-threaded rod 29 cooperating with an internally screw-threaded bore in a knob 30, whereby the tension of the spring can be adjusted; the spring 28 maintains the surface 37 of the member 33 in contact with a friction wheel 23 of rubber &c. on the shaft 21 so that the member 33 is rotated. The workpieces are pressed down upon the abrasive medium on the upper surface of the lapping disc by the weight of the member 33 and the rod 31; the pressure can be increased by placing weights on the upper end of the rod 31 rotating upon a flange 32. For changing the lapping disc the arm 18 can be locked in an out-of-the-way position by a locking pin 35. Two or more attachments may be used for workholding on one lapping disc at the same time. A work carrier for irregular or non-flat objects 34 has a hollowed-out portion filled with a matrix 38 into which the objects are pressed. A work carrier for flat objects has a flat lower surface to which the objects are attached, e.g. by cement. For dressing the lapping disc, a rotary member 41, Fig. 5, coated on its bottom surface with abrasive, is substituted for the work carrier 33. The diameter of the bottom surface is substantially equal to the radius of the lapping disc, and the bottom surface is provided with shallow radial grooves 42. By using successively finer grades of abrasive on the dressing member 41 any unevenness and lack of flatness of the surface of the lapping disc is gradually removed. In a modification, Figs. 6 and 7, one end of the arm 18 is arranged on the top of the column 17 and pivoted about the axis of a clamping member 43. The latter comprises a screwthreaded portion 44 engageable in a screwthreaded hole in the top of the column 17, a cylindrical portion 46 fitting inside a vertical bore in the arm 18 to form a pivot for the arm, and a portion 47 the lower face of which abuts against the upper face of the arm 18 when the member 43 is screwed tight. A lug 49 on the column 17 carries a micrometer screw 51 co-operating with a lug 48 on the arm 18 to effect angular adjustment of the arm. A shaft 54 having on its lower end a partspherical surface 58 for engagement with a part-spherical cavity in the rotary member is mounted in a bush 53 secured in the guide block 26 by balls 59 carried in a cage 56.