Patent GB-1434791-A (GB)
Title: Reciprocating hand tool
IPC: B24B23/04
Filed: 1973-04-13
Abstract: 1434791 Abrading L U SHAPIRO 13 April 1973 18002/73 Heading B3D [Also in Divisions F1 and F2] A hand tool comprises a housing 11, Fig. 1, having an apertured wall part 39 with a substantially planar surface bordering the aperture, an air motor 19, 21 mounted in the housing, means for delivering and exhausting fluid to and from the housing and air motor, a tool mounting member 41 mounted for reciprocating motion on the housing with a substantially planar surface thereof parallel to that of the apertured wall part, means 25, 27, 31 interconnecting the motor and member for reciprocation of the latter and for holding the member in spacial relationship to the wall part whereby fluid exhausted from the interior of the housing through the aperture forms a fluid bearing between the planar surfaces of the wall part and the tool mounting member.  The body 11 has forward and rear handles 13, 15 and supports the cylinder 19 of the air motor, the cylinder containing a piston 21 connected by a clevis 23 to one end of a link 25. The other end of the link is connected by a pivoted link 27 to a second link 31 in turn connected to a clevis 33 slidable in a slot 37 formed in a bearing plate 39 having a longitudinal groove 113, the plate and groove comprising the apertured wall part and its planar surface. The clevis is secured by screws and/or rivets to a shoe bar 41, constituting the tool mounting member, which carries a sanding plate 43, cushioning pad 45 and sandpaper 47. The piston reciprocates in the opposite directions to the bar, plate, and pad and has substantially equal mass. A valve 51 is secured to the body 11 and has a closure ball 57 which can be lifted from a seating 55 against the bias of a spring 59 when a trigger 67 is actuated to move a pin 71 so that air supplied to a fitting 63 can pass to the motors 19, 21. During initial movement of the pin, air is directed to a passage 81 leading to a cylinder chamber 83 so that the piston moves from its controlling biased position. Further movement of the pin closes the passage 81 and directs the air to a passage 85 leading to a peripheral groove 89 in the piston, a radial passage 91, and a longitudinal passage leading to the chamber 97 at the other end of the cylinder to reverse the direction of movement of the piston. The exhaust of air from chamber 83 is closed to effect cushioning of the movement of the piston. As the piston passes its central position, air is directed by a passage 87 to a peripheral groove  107 in the piston, radial passage 105, a longitudinal passage and the chamber 83 to again reverse the direction of movement of the piston. The air exhausted from ports 109, 111 of the motor is directed into the longitudinal groove 113 and the shot 37 in the bearing plate so as to enter the space surrounding the links 25, 27, 31 in the body. As the pressure builds up in the body, air pressure also acts between the plate 39 and bar 41 as an air bearing, the separation of the plates being limited by brackets 117, Fig. 2. In another embodiment, the supply of air pressure to chambers 213, 215, Fig. 1, at opposite ends of a piston 211 is controlled by a valve spool 223 which has a gear 222 in mesh with a rack on a rod 219 reciprocated with the piston. The spool has axially aligned blind bores 237, 239, Fig. 10, which are separated by a wall 241 and each of which has a respective radial passages 245, 249 leading to chambers formed in a valve body 235 by dividers 257, the chambers being connected by passages to the chambers 213, 215 at the ends of the piston. As air is exhausted from the blind bores it passes through passages 259 into the body 11 to build up pressure therein and between the bottom of the body and the shoe 41 to act as an air bearing.