Broaching device and method

A broaching device for enlarging an opening, hollow or cavity in a workpiece, the device comprising:

• a lathe having a tailstock and a rotary workpiece mounting chuck;
• a ballscrew shaft having a helical raceway groove formed externally on the shaft;
• a ballscrew nut carried on said tailstock and mounted on said ballscrew shaft, the nut being provided with an internally-formed helical raceway groove;
• load bearing balls in said raceway grooves to transfer motion between the nut and shaft;
• said nut being axially stationary and said shaft being axially movable with respect to the nut;
• and a broaching tool mounted on the shaft so as to be axially movable therewith.

A broaching device for forming openings in workpieces having openings with marginal surfaces to be broached pre-provided therein, the device comprising:

• drive transmitting mechanism including a rotary first machine tool part and an axially spaced, axially movable second machine tool part;
• a screw and nut assembly connected with one of said first and second parts and incorporating a screw mounting a nut;
• a broaching tool immovably mounted on one of the screw and nut and projecting axially from said assembly;
• one of said first and second machine tool parts comprising a workpiece holder and the other machine tool part a mount for said screw and nut assembly so that the frictional resistance between said tool and marginal opening surface of a workpiece held in said holder, created by rotation of said first part after said parts are moved axially to engage said workpiece and tool, causes said screw and nut to move relatively axially to relatively axially feed said tool and workpiece marginal surface with mechanical advantage in the broaching operation.

A method of broaching openings in workpieces to a desired size and configuration using a ball screw and nut assembly incorporating a ball screw and nut configured to provide a recirculating raceway between them which includes ball return portions;

• load bearing balls accommodated in said raceway to transfer motion between the ball screw and nut;
• a broaching tool of greater lateral extent than said openings being provided on one of the ball screw and nut to project axially from said assembly;
• and drive transmitting members being provided for moving the workpiece and the ball screw and nut assembly relatively axially and in relative rotation;
• the steps of:
• (a) from a remote position moving the workpiece and the ball nut and screw relatively axially to move the tool into frictional engagement with the surface of one of said openings;
• and
• (b) causing the tool and workpiece to be frictionally co-rotate and the tool and workpiece to feed relatively axially to broach the workpiece opening via consequent mechanically advantaged interaction of the ball nut and screw assembly.

A method of broaching comprising:

• (a) providing axially spaced apart relatively rotatable and relatively axially movable machine tool members;
• (b) mounting a workpiece having an opening with marginal surface to be broached on one of said members;
• (c) mounting a broaching tool, connected via a nut and screw assembly to the other member, in axial alignment with the workpiece;
• (d) relatively rotating said machine tool members;
• (e) relatively axially moving the machine tool members to bring the tool and workpiece marginal surface into frictional engagement to cause the workpiece and tool to relatively feed axially as a result of mechanically advantaged interaction between the nut and screw of the nut and screw assembly.