Patent GB-1458107-A (GB)
Title: Orbital sanders
IPC: B24B23/04
Filed: 1974-03-29
Abstract: 1458107 Orbital sanders ROBERT BOSCH GmbH 29 March 1974 [31 March 1973] 13968/74 Heading H3D An orbital sander comprises a sanding plate 13 suspended by elastomeric pillars 14 from a housing 10 and drivable by an eccentric 24 driven from a motor 11, a change-over member 56 for selectively enabling the plate to be driven in an orbit or reciprocated in a substantially linear path, and two counterweights 26, 27 rotatable about a common axis in such a way that they have the same direction of rotation when the sanding plate is driven in a rotary orbit and have opposite directions when the plate is reciprocated in a substantially linear path. The motor 11 has a shaft 15 which drives a pair of interconnected pinions 17, 18. pinion 17 meshes with an intermediate gear 20, in turn, meshing with a gear 35 and pinion 18 meshes with a gear 33 of a first support member 28 which carries one 27 of the counterweights and is rotatably mounted by needle bearings 31, 32 on a shaft 21 supported by bearings 22, 23 in the housing 10. The other counterweight 26 is secured by a pin 25 to the shaft 21. The gear 35 driven by gear 20 and pinion 17 is mounted on a second support member 36 which is rotatably supported in the housing 10 by a bearing 36 and is in telescopic engagement with an extension 29 of the first support member 28; a flange 38 on the second member 36 extends towards the shaft 21. A slide member 40 is axially displaceable in a recess 39 in the upper part of the shaft 21 by movement of a eccentric pin (52, Fig. 3, not shown) upon rotation of a control shaft (51), the pin engaging a groove 50 in the member 40 which, at its lower end, has a cross-bore containing a bush 42. A spring- loaded ball 44 is selectively engageable with a groove 47 in the first support member 28 or with a groove 45 in the second support member 36 according to the axial position of the slide member 40. In the lower position shown in Fig. 2 in which the ball engages the groove 47 in the first support member 28, the pinion 18, be engagement with gear 33, rotates the second support member 28 which, because of the engagement of the ball in groove 47, also rotates shaft 21 so that both counter-weights rotate in the same direction. When the slide member is moved to its upper position, the ball engages the groove 45 of the second support member, which because of gear 20 is driven in the opposite direction to the first support member 28 so that the shaft 21 with counterweight 26 is driven in the opposite direction to the first support member 28 and counterweight 27. The change of rotation of shaft 21, which has an eccentric 24 for imparting motion to the sanding plate, also changes over the motion of the sanding plate from orbital to reciprocation by means of a device 55. The eccentric 24 is secured to a bush 65 having a bore 66 for a bell 68 which is spring urged through a radial bore 56<SP>1</SP> in a swivel member 56 and into engagement with a groove 69 in a plate 60. The swivel member 56 has vanes 57, 58, which in the position shown in Fig. 2, engage the walls of a housing 70 which receives the plate 60 and is secured to the sanding plate 13. The plate 60 has opposed recesses aligned with bulges 71, 72 on the housing 70. In the position shown and with the shaft 21 and eccentric rotating anticlockwise, and the counterweights rotating in the same direction, the ends of the vanes 57, 58 engage the housing so that a rotary orbital motion is imparted to the sanding plate. When shaft 21 is rotated clockwise and the counterweights rotate in opposite directions, the swivel member 56 moves so that the vanes 57, 58 abut side surfaces 61, 62 of the recesses and are aligned with the bulges so that only longitudinal reciprocating movement is imparted to the sanding plate.