Method of and apparatus for feeding nonround-section bars to screw machines

A method of feeding an elongated profiled bar to a screw machine having a headstock whose collet has an openable aperture that complements the cross-sectional shape of the bar and wherein the collet is closed on the bar and driven at a relatively high rotational speed during machining of the bar, said method comprising the steps of:

• a. detecting the rotational speed of said collet and generating a speed output only when said rotational speed lies within a predetermined range;
• b. holding said aperture open and pushing the bar forwardly longitudinally toward said collet only in response to generation of said speed output, whereby the bar and said aperture are aligned the former can pass forwardly through the latter;
• c. closing said collet on the bar only when same has passed forwardly through said aperture;
• d. generating a position output only when the bar has been passed forwardly through said aperture;
• and
• e. withdrawing the bar backwardly from said collet after step b) when a predetermined time period elapses after generation of said speed output and before generation of said position output, whereby when said aperture and the bar do not align in step (b) it is possible to repeat this step (b).

In combination with a screw machine having a headstock provided with an openable and closable collet rotatable at high speed and having a throughgoing aperture of a cross-sectional shape complementary to that of a bar to be machined at said high speed, a feed apparatus comprising:

• means for detecting the rotational speed of said collet and for generating a speed output only when said rotational speed lies within a predetermined range;
• means for pushing the bar forwardly toward said aperture only in response to generation of said output, whereby when the bar and said aperture align the former passes forwardly through the latter;
• means for generating a position output when the bar has been advanced forwardly through said aperture;
• timer means for measuring the time elapsed after generation of said speed output and before generation of said position output;
• and
• means connected to said timer means for withdrawing the bar backwardly from said collet after pushing of the bar toward said collet when the time elapsed after generation of said speed output and before generation of said position output exceeds a predetermined limit.