Taper thread cutting machine and method

A tapered thread cutting machine for threading work of different size comprising a rotary machining head having an axis of rotation including a recess having planar interior walls, each parallel to the axis of the head, a plurality of tool holders in said recess engaged with said walls and each other for opening and closing movement in response to movement of one of said holders, a projection on said one of said holders, a spring loaded control rod extending transversely of said axis of rotation of said head and removable secured to said projection and including a thrust shoulder, a thrust block entirely guided for linear movement and engaging said thrust shoulder, an axially extending control key having a linear cam surface in engagement with said thrust block whereby axial movement of said control key moves said control rod and thus said tool holders, said set-up change means to vary the distance between said thrust block and said projection to thread work of different size.

A taper thread cutting machine for cutting taper threads on the end of a bar comprising a rotary head having an axis, a plurality of interfitting chaser holders mounted in said head for rotation therewith and for uniform closing movement, actuator means for actuating said interfitting chaser holders, clamp means for clamping a bar end centered with respect to said head against rotation, stop means for positioning a bar end for clamping, feed means for feeding said clamp means and thus the bar end axially into said head as the head rotates, first drive means for driving said feed means axially at a first speed, second drive means distinct from said first drive means for driving said rotary head rotationally at a second speed, and speed-control means for controlling a read speed of said first drive means in response to the speed of said second drive means to ensure uniform pitch for the thread being cut.

A tapered thread cutting machine for threading work comprising a rotary machining head having an axis and including a square recess having four planar interior walls each parallel to the axis of the head, a plurality of tool holders in said recess engaged with said walls and each other for opening and closing movement in response to movement of one of said tool holders, said tool holders each including removable chasers supported at a uniform taper angle, said tool holders further including a removable insert supporting pre-coning means for pre-coning such work for engagement by said chasers, said pre-coning means having a triangular cutting tool having three cutting edges, and means supporting said cutting tool on said insert for convenient indexing to prevent a new edge to the bar as one edge wears.

A set-up process for a taper thread cutting machine for work of different size of the type having a rotary machining head having an axis and including a recess having planar walls accommodating a plurality of tool holders engaged with the walls and each other for opening and closing movement, a projection on one of said holders, and one of a set of control rods removable secured to said projection each including a thrust block stop shoulder for engaging a thrust block which in turn engages a linear cam movable axially of said head to close said tool holders uniformly on the work, said control rod having a predetermined shoulder-projection dimension from said projection to said shoulder, said dimension being related to the size of the work, the set-up process comprising the steps of:

• removing said one control rod;
• and installing another selected control rod of said set dimensioned to provide a different shoulder-projection dimension.

A taper thread cutting machine for different size reinforcing bars and the like comprising a rotary head having an axis and having an internal cavity with planar walls, a plurality of interfitting chaser holders mounted in said cavity for uniform movement along said planar walls as a bar moves axially within the head;

• a longitudinally extending cam engagement a set means which engages one of said holders for moving each of said holders uniformly;
• said cam including profile means for controlling the taper angle of the thread, said chaser holders having a starting position;
• and said set means being entirely guided for linear movement and for setting said starting position of said chaser holders with respect to said cam to cut threads on such different size bars.

A process for cutting taper threads on the end of a bar comprising the steps of gripping the bar in a vise;

• rotating a machining head having an axis and including a plurality of tool holders each being movable uniformly radially for opening and closing movement, each tool holding including a chaser and an insert holder for a pre-coning cutting tool having plurality cutting edges;
• and axially moving said vise and thus the bar gripped by said vise towards said machining head and actuating said machining head so that the pre-coning cutting tool engages the bar end initially to cut a conical surface on the bar which is then engaged by the chaser to cut threads on such conical surface, and said process further comprising the step of supporting the pre-coning cutting tool on said tool holder for convenient indexing to present a new edge to the bar as one edge wears.