Power actuated tools with power adjustment means

PCT No. PCT/AU96/00590 Sec. 371 Date Dec. 23, 1998 Sec. 102(e) Date Dec. 23, 1998 PCT Filed Sep. 18, 1996 PCT Pub. No. WO97/13620 PCT Pub. Date Apr. 17, 1997According to the present invention there is provided an explosively-actuated tool for use in setting fasteners into a substrate, comprising a barrel (2), a driving piston (6) mount within the barrel for driving the fastener into a substrate upon detonation of an explosive charge positioned at or adjacent the rear of the barrel, a firing chamber (8) defined in the barrel rearwardly of the piston, and a system capable of controlling the power of the tool by controlled venting of combustion gases from the firing chamber. The power control system comprises an exhaust port arrangement (14) leading from the firing chamber through the wall of the barrel, and a control member (16) for controlling the effective open area of the exhaust port arrangement. Particularly advantageously, the end of the control rod is provided with a concave arcuate control edge (16b) which provides a relatively uniform relationship between displacement of the control rod and the degree of opening of the exhaust port arrangement. Such a control edge can be formed by a simple chamfer at the end of a cylindrical control rod (16) with the passage also being cylindrical.