Patent GB-1510752-A (GB)
Title: Pneumatic fastener driving or impacting apparatus
IPC: B25C1/04
Filed: 1976-01-23
Abstract: 1510752 Pneumatic nail driver H M HAYTAYAN 23 Jan 1976 [5 Feb 1975 4 Dec 1975] 02631/76 Heading B4C A pneumatic nail driving apparatus comprises a cylinder 40, piston 49, hammer 47 attached to the piston, air reservoir 54, air manifold 58, poppett valve 17 and control valves 64, 88. In the equilibrium position shown in Fig. 3 the air reservoir, the space below the piston and the space above the poppet valve are all at the manifold pressure. When foot 107 of the apparatus is pressed against the workpiece safety rod 109 causes valve 88 to close off the passage to reservoir 54 and allow the air in cylinder 40 to exhaust to the atmosphere. Movement of trigger 82 then causes valve 64 to allow the space 75 above the poppet valve 17 to exhaust to the atmosphere. The air pressure in reservoir 54 lifts the poppet valve. Piston 49 is thus exposed to the high pressure reservoir air and is accordingly forced downwards so that hammer 47 drives nail 134. Preferably the orifice 91, between valve 88 and air reservoir 54 is larger than orifice 67 between valve 64 and manifold 58 in order to avoid building up the pressure in reservoir 54 faster than in cylinder 40 when compressed air is first applied and thereby prevent movement of piston 49 before trigger 82 is pulled. If the hammer diameter is at least 20 : 1 of the piston diameter and the air pressure exceeds 175 p.s.i. it is possible that if the trigger 82 is pulled when the safety rod 109 is not activated the piston may be pushed slowly downwards (the free end of hammer 47 experiences only atmospheric pressure). Accordingly trigger 82 may be locked against movement by spring biased crank 165, Fig. 6, unless the apparatus is pressed against the workpiece with sufficient force to retract a second safety rod 162. First safety rod 109 may also be spring biased. The maximum hammer impact force is obtained if the hammer does not move significantly until the poppet valve is fully opened. This is obtained by restricting the cross-section of the channel from cylinder 40 to the atmosphere. The restriction may be provided by the narrow bore 182, Fig. 9, of an auxiliary valve in the exit port of valve 88. After poppet valve 17 has fully opened and piston 49 has moved through 40-80% of its stroke the pressure built up in cylinder 40 overcomes the resistance of spring 180 and moves valve member 178. Air is then exhausted via wide passages 176, allowing continued acceleration of hammer 47. Preferably hammer 47 projects 3/16th inch beyond the end surface 118 of foot 107 before piston 49 commences to compress cushion 52. The movement of the hammer beyond the end surface will cause the tool to recoil from the work surface, freeing rod 109 and allowing valve 88 to resume the position shown in Fig. 3. High pressure air will thus flow from reservoir 54 to the lower part of cylinder 40 thereby helping to decelerate piston 49 and then returning it to the ready position (Fig. 3). Magazine nails 134 whose shanks are embedded or frictionally disposed in plastic sleeves 135 formed as a continuous strip are urged towards the firing position by spring biased pusher 140, in disposable or reusable magazine 8, Fig. 3.