Patent GB-1070787-A (GB)
Title: Impact tool
IPC: B25B27/00
Filed: 1964-07-03
Abstract: 1,070,787. Percussive tool. OMARK INDUSTRIES Inc. July 3, 1964 [July 3, 1963], No. 27573/64. Heading B4C. [Also in Divisions B8 and H2] A percussive tool which may be used for driving a stud, comprises an impact piston 25 movable in a cylinder 23 and driven after fuel from a supply chamber (113, Fig. 7) has been ignited by means of a trigger-actuated firing mechanism (48, Fig. 12) and a metering chamber (131) for the fuel connected, via first and second valves (78 and 44, Fig. 3) with the supply chamber and cylinder respectively, the second valve being actuated by the trigger after the first valve has been closed. An auxiliary piston 21 is mounted in a cylinder head 22 and is adapted to be pulled against the action of a spring 24 by a handle 267 into a cocked position in which a flange 144 on the piston 21 is engaged by a pivoted sear (212, Fig. 12) forming part of the trigger mechanism (48). A trigger 40 is connected to a link (184) having a pivoted abutment (203) which, when the trigger is pulled, contacts the sear (212) to release the loaded piston 21. A lever (185) is pivoted on the trigger and is coupled by a hook (189) with the armature (234) of a magneto ignition device (47); the lever 185 is held in the cocked position by means of a pivoted latch (190). The metering chamber (131) is formed by means of two members (63, 64) mounted in the cylinder head 22, the member 63 having a resilient seat 82 for the first valve 78 which includes a resilient seat 75 for the second valve member 44. In operation, the tool is cocked by pulling the handle 267 so that the flange 144 of the piston 21 is latched behind the sear 212. In this position the first valve 78 is held off its seat so that pressurized fuel from a refillable screw-on cartridge (97) is fed into the measuring chamber 131 (Fig. 3); the valve is held open by means of the flange 144 abutting a pivoted lever (145, Fig. 9) which is coupled to a rod (152) having abutments (171, 172) engaging an arm 41, the arm being connected to a collar 42 (Fig. 7) on the second valve 44. Upon actuating the trigger, the piston 21 is released and, under the action of a spring 24 first strikes the impact piston 25 which then draws air into the cylinder. Towards the end of the stroke of the piston 21, the flange 144 strikes the end 163 of the abutment 171 to thereby move the valve 44 so that it allows the first valve 78 to close and, at the same time, the end of the second valve to be lifted from its seat; the fuel then flows from the measuring chamber via a channel (45) in the valve member 44, into the cylinder. At the end of the stroke of the piston 21, the flange 144 strikes an abutment member. which via a rod (222 Fig. 12) causes a dog (227) thereon to strike the latch 190 and thereby release lever (185). The magneto is then actuated and causes a sparking plug to ignite the explosive charge in the cylinder. The explosion moves the piston 25 forwardly so that a ram 26 drives in a stud located in a barrel 36. The force of the explosion also acts on the front end of the piston 26 so that it is automatically driven back to its cocked position.