Patent GB-1216238-A (GB)
Title: Improvements in or relating to power-driven abrasive tools
IPC: B24B23/04
Filed: 1968-05-17
Abstract: 1,216,238. Sanding. BLACK & DECKER Ltd., and J. J. DONNELLY. 30 April, 1969 [17 May, 1968], No. 23617/68. Heading B3D. A power-driven abrasive tool for use with a rotary power unit includes a housing for receiving the driven shaft of the power unit and a backing plate which is arranged, in use, for operative connection to the drive-shaft, the backing plate and the housing being mounted on opposite ends of a number of retaining pillars, made entirely of elastomeric material, one end of each pillar being so shaped that the backing plate may be detachably fastened thereto. An orbital sander attachment for an electric power drill comprises a rectangular backing plate 2 having rotatable rods 3, 4 clamping the ends of a sheet of paper-backed abrasive paper 5 so that the sheet is held taut against a pad 6 of felt, sponge rubber &c., adhesively secured to the underside of the plate.  The plate 2 is mounted on a housing 1 formed with a pair of lugs 7 engaging slots 8 in the casing 9 of an electric drill 10; the slots may also serve as ventilation apertures for the drill motor. To prevent vibration between the attachment and the drill, the housing has a sliding block 11 formed with tabs 12 engaging other slots 13 in the drill casing 9; the block is moved by a knob 14. Into the drill drive spindle 17 is screwed the shank 18 of an eccentric counter-balance 19 having a counter-weight 20 and an eccentric shaft 21 rotatable in a plain bearing 22 secured to the plate 2. The plate 2 is secured to the housing 1 by four retaining pillars moulded entirely from elastomeric material, e.g. rubber, each pillar comprising a body 23 of generally square crosssection, a housing engaging end 24 and a backing plate engaging end 25. The plate 2 has four square holes 26 formed in circular raised portions 27. When a pillar is assembled to the plate 2 the edges of the hole 26 surround a portion 25 of substantially square cross-section and are sandwiched between a circular terminal portion 29 and a flared portion 30. To assemble the plate 2 with the housing 1 each frusto-conical part 31 is forced upwards past an annular rib 32 provided within a generally cylindrical locating member 33 formed in the housing 1, so that the rib surrounds a cylindrical portion 34 and is sandwiched between the underside of the part 31 and the upper surface of a tapered portion 35. The portion 35 has four identical faces which are trapezoidal in form and engage complementary portions 36 in the member 33 to prevent relative rotation between the pillars and the housing 1. In a modification, Figs. 5 and 6, each pillar has a frusto-conical upper end 37, a cylindrical body 38, and a circular disc-like lower end 39. The pillars are clamped to a backing plate 40 by two strap-members 41 which also hold in position rods 42 for clamping the abrasive sheet. Each strap member has a pair of circular holes 43 having a diameter intermediate between those of portions 38, 39; the pillars are inserted into the strap members so that the portions 39 abut the underside thereof. Each strap member is secured to the backing plate 40 by nut 44 and bolt 45. Each end of the backing plate has a pair of upturned lugs 46 entering slots 47 in the strap-members to locate them. The backing plate also has four raised portions 48 each arranged in co-operation with a respective lug 46, to hold in position the lower end of a pillar. The upper ends of the pillars may be secured to the housing in the way previously described, or they may be plugged into holes in a pair of clamping plates each of which is detachably secured to the underside of the housing vertically above a strap member 41. The housing 1 and electric drill may be formed integrally. The electric drill may be replaced by a pneumatically operated drill or by any power unit for rotating the spindle 17.