| 摘要 |
This invention relates to an improvement in a hand drill with a pneumatically-hydraulically controlled advance and including a housing, a drilling drive unit adapted to be powered by compressed air and being displaceably guided in said housing by a piston and cylinder, and further including hydraulic lines, and control valves, the improvement comprising a rotatable support sleeve means secured to said housing and adapted to rest on the surface of a workpiece and surround a drill bit, said piston being a double-faced hollow advance piston means mounted in said cylinder so as to divide said cylinder into two chambers, one chamber together with one face of the advance piston means being adapted to be acted on by the compressed air, and the other chamber being adapted to be filled with hydraulic fluid and pressure-loaded by the other face of the advance piston means, said latter chamber communicating through hydraulic line means and a throttling back-pressure valve means with a cylinder means having a compensating piston means therein, said cylinder means being positioned in hand grip means connected to said housing, said advance piston means on one cylinder side being adapted to displace the hydraulic fluid against said compensating piston means thus pressure-loaded until a drilling depth adjusted by a limiter means mounted on said housing is attained or until a continuously adjustable switch means mounted in a pneumatic line is deactivated, whereby the pressure acting on the compensating piston means returns the drilling drive unit together with the advance piston means to the initial position thereof. |
