Patent GB-1183947-A (GB)
Title: Power Tool for Surface Finishing Workpieces
IPC: B24B23/06
Filed: 1967-07-07
Abstract: 1,183,947. Belt sander. ROCKWELL MFG. CO. 7 July, 1967 [7 July, 1966], No. 31518/67. Heading B3D. A power tool, for surface finishing workpieces, having spaced apart idler and drive pulleys around which an endless surface finishing belt is trained in use, said pulleys being rotatably mounted on a frame, and a motor means connected to said drive pulley, is characterized in that: (i) the end portions of said idler pulley are of smaller diameter than the intermediate portion therebetween to provide that part of the belt which is operatively tensioned around the periphery of said idler pulley with a crowned configuration; (ii) said drive pulley is uncrowned and flanged; and (iii) at least one of said pulleys has a substantially cylindrical, hub-mounted, elastically deformable body formed with annular, circumferentially extending, outwardly opening grooves defining a multiplicity of circumferentially extending belt-engaging ribs. A portable sanding machine comprises a frame 20 rotatably supporting a pulley assembly 22, driven by an electric motor 28 carried by the frame, and an idler pulley assembly 24; an endless sanding belt 26 is trained round the pulley assemblies. The motor shaft 42 drives, through gears 60, 62, 74 in a housing 56, a shaft 76 carrying the pulley assembly 22 which comprises a rigid metallic hub 100 and a resilient annulus 102 of elastomeric material having ribs 280 of uniform diameter separated by grooves 282 such that one rib does not objectionably interfere with an adjacent rib if it is flexed. Pulley flanges 110, 112 are provided. A bracket 120 integral with the gear housing 56 has a split collar 122 receiving one end of a tube 124 clamped by a screw 130 passing through ears 126, 128 into a nut 132. A fender plate 134 integral with the bracket 120 deflects particles downwardly and rearwardly. The forward end of the tube 124 supports the idler pulley assembly 24 comprising roller units 140, 141. The roller unit 140 comprises a rigid hub 146 and a resilient annulus 144 of elastomeric material having ribs 280 of uniform diameter and an outer rib 288 of smaller diameter; the roller unit 141 is of the same construction. The roller units 140, 141 are carried by a plunger 142 slidably and rotatably received in the tube 124 and formed with a flat-sided plate section 160, acted on by a spring 164 in the tube 124 to tension the belt 26. A bracket assembly 170 mounted on the forward end of the tube 124 comprises a clamping block 172 fixed to a support bracket 174, the block having a groove co-operating with the face of the bracket to form a semi-circular channel 176 receiving the notched forward end of the tube 124. The bracket 174 has a groove 180 through which the lower section of the plate section 160 freely extends with sufficient clearance on both sides to allow the plunger 142 to be turned in either direction through a limited angle about the axis of the tube 124. Arms 182, 184 extend from the plate section 160 and when the plunger 142 is in its forwardly biased position the undersides of the arms seat against the top of the bracket 174 to prevent angular movement of the plunger 142. The arm 182 has a notch 186 located forwardly of the bracket 174 when the plunger 142 is in its forwardly biased position. With the plunger 142 in a retracted position the notch 186 is aligned with the bracket 174 and a slight rotation of the plunger 142 aligns the rear edge 190 of the notch with the rear face of the bracket 174 to latch the plunger 142 in retracted position to remove the tension of the belt 26 facilitating its removal. The lower workpiece-engaging run of the belt 26 is supported by a shoe 200 removably mounted on the frame 20. The shoe comprises a resilient pad 202, e.g. of one or more layers of polyurethane between a rigid facing plate 204 and a rigid backing plate 206. The belt tension holds the plate 204 against the pad 202 and the backing plate 206 against the bottom faces of the bracket 174 and a mounting plate 208 secured to the collar 122. Tongues 212, 220 on the backing plate 206 are received in a groove 214 in the bracket 174 and in a groove (222) in the mounting plate 208. The shoe 200 is reversible end for end, and the facing plate 204 may have its forward and rear ends of differing configuration. A covering (223), e.g. of material similar to that of the belt, may be adhered to the bottom face of the pad 202; the facing plate 204 may then be removed to provide the lower belt flight with greater flexibility. A forward handle 226 is fixed to a mounting bracket 230 removably fixed to the tube 124. A rear handle 238 is mounted on an extension 240 of the end plate 53 of the motor 28. At the inner end of the handle 238 is an actuator 250 operable by the thumb of a workman grasping the handle and actuating a toggle switch in the motor circuit. A fan 246 on the motor shaft draws air into the motor housing 30 through ports (36) at the rear of the motor and discharges it through ports 248 at the front of the motor to form a protective air screen parallel to the plane containing the inboard edge of the belt 26 to deflect dust and chips away from the workman's face. A belt guard 290 disposed above and parallel with the upper belt flight has its rear end extending partially round the pulley assembly 22. The forward end of the guard is detachably secured at 292 to the frame 20 and the rear end is secured to the gear housing 56.