Patent GB-693430-A (GB)
Title: Improvements relating to pneumatically operated hand tools
IPC: B24B23/02
Filed: 1950-01-16
Abstract: 693,430. Grinding; sawing. PAGE, V. J. April 16, 1951 [Jan. 16, 1950], No. 1035/50. Classes 60 and 145 (ii). [Also in Group XXVI] A pneumatically operated hand tool has adjustable means for restricting the exhaust of the air motor so as to control the speed. The compressed air motor 1 comprises three radially disposed cylinders 2, the pistons 4 being connected by rods 3 to a single throw crankshaft 5; the cylinders are carried by a base plate 7 having a bearing 8 for the inner end of the crankshaft. The outer end of the crankshaft is journaled in a bearing 11 carried by a central boss 12 of a head plate 13 secured to the cylinders. The outer end 10 of the crankshaft, the bore of the head plate boss 12 and of a boss liner 15 are ported so as to constitute rotary valve means for controlling the flow of compressed air into and out of the cylinders. The admission of compressed air to the rotary valve means is effected via a control valve 16 carried by head plate 13. The valve plunger 18 is loaded by a spring 39 so that the valve is normally closed; the valve is opened by depressing a trigger 34 pivoted at 35 on the hand grip 20. A compression spring 36 is interposed between a tappet 37, slidable on the trigger 34, and the valve plunger. A spring-biased stop pin 38 or ball catch retains the trigger in depressed position to relieve the operator of the necessity of holding the valve open. Exhaust air from the cylinders passes into the bore 41 of shaft end 10, this bore terminating at one end in a constricted orifice 42 and at the other end in a wide-mouthed recess 43, the rate of escape of air from the recess 43 being controlled by a disc 44 axially adjustable by a screw 46. Air can always escape through the orifice 42 even when the recess 43 is completely blanked-off by the disc 44. The crankshaft 5 drives, through gears 49, 50, a shaft 52 rotating in bearings 54, 55 in the barrel portion 23 formed integral with the base plate 7. A cross hole 57 in the shaft 52 receives a tommy bar for the purpose of holding the shaft 52 against rotation when attaching a tool element on or removing it from the screwthreaded spigot 60 at the end of the shaft 52; the tommy bar is inserted through one or other of a pair of openings in the barrel 23, the openings being normally closed by a sleeve 61 rotatably mounted on the barrel 23, the sleeve 61 being twisted to bring holes 62 therein into register with the barrel openings when the tommy bar is to be used. The bearings 54, 55 are spaced apart by a liner 63, shims 64 being interposed between the bearings and liner, the assembly being retained by a flanged bush 65 screwed into the end of barrel 23; the shaft 52 is formed with grooves 66 flanking opposite sides of a central collar 67, so that any dust or swarf entering the interior of the liner 63 is flung off the rotating shaft 52 and packs into the end corners of the space within the liner 63 adjacent shims 64, the latter preventing dust or swarf creeping into the bearings 54, 55. Lubricant is supplied to the shaft 52, via a groove 69 in the outer surface of liner 63, through a nipple 70 which co-operates with a slot 71 in the sleeve 61 to limit the rotation of the sleeve around the barrel. Lubricant is supplied to the gears 49, 50 through hole 73 having screw plug 74. Lubricant is supplied to the air motor by an oiling device 75 operating as described in Specification 689,840, [Group XXXIV].  A series of interchangeable adaptors of different lengths, such as the short adaptor 76, are provided for attachment to the spigot 60 of the shaft 52; for surrounding long adaptors detachable guard tubes are screwed into the threaded bore 77 of bush 65. An auxiliary handle 78 may be provided, having a hand grip 81 and a split collar 79 clamped on barrel 23 by a screw 80. The tool may carry a grinding wheel 83 and a guard 84, having a split collar 86 clamped by screw 87 to the barrel 23; the guard 84 has a removable handle 85, the auxiliary handle 78 being dispensed with. A cup-like spinner 88 clamped between the wheel 83 and a flange 89 on adaptor 76 is arranged with its rim 90 just clear of the floor of an annular recess 91 in the guard 84; the end of barrel 83 projects beyond the recess, and the rotation of the spinner 88 creates a draught which prevents dust or swarf entering the barrel 23. The tool may carry a buffing pad 82. The tool may carry a circular saw 92 housed in a semi-circular guard 94 carrying a sectorshaped shield 95 normally urged by spring means to a position in which it covers the lower part of the saw; the shield 95 is retained in open position by a spring-loaded plunger 96 carried by guard 94 and engaging an opening in the shield. A face plate 98 adapted to slide over work being sawn is mounted on the guard 94 so as to be capable of tilting in a longitudinal and/or transverse direction. A reversible fence 99 is mounted on the face plate 98.