Tool control head for pipe and tubing cutting machine

A machine tool device for advancing a tool against a work specimen, comprising:

• first means including a first piston within a housing and an output shaft connected to move with said first piston, said first piston being advanced in response to application of air under pressure to a first surface of said first piston;
• a free turning tool on said output shaft;
• a closed hydraulic circuit within said housing including a second piston and first and second chambers, one on each side of said second piston, said second piston being operatively connected to said first piston such that the volume of said first chamber decreases as said first piston is advanced;
• second means comprising at least one check valve and a corresponding associated first passage for controlled transfer of hydraulic fluid between said first and second chambers, said check valve having an inertial characteristic such as to close said first passage in response to hydraulic pressure against said check valve as said first chamber volume decreases, said closure being at a time corresponding to a first predetermined point of said tool advancement as permitted by said check valve inertial characteristic;
• third means comprising a by-pass passage and variable flow valve between said first and second chambers, said by-pass permitting hydraulic flow between said first and second chambers at a reduced rate compared to the flow through said check valve prior to its closure, said reduced flow rate permitting continued advancement of said tool from said first predetermined point to a second predetermined point at a reduced velocity;
• and
• resilient fourth means for restoring said first piston and therefore said tool to a withdrawal point when said air pressure is released, said check valve contemporaneously opening to permit relatively rapid back flow of said hydraulic fluid from said second to said first chamber.