Spindle axial location must be accurately maintained while contours are being precision machined with a tracer lathe. To determine existing inaccuracies, spindle expansion of three lathes was measured for various operating conditions. In all cases, when the spindle rpm was varied (200-660) to simulate approximate constant surface cutting speeds, the axial expansion was too large (0. 00005 to 0.00025 inch) for ultra precision contour work. If present lathes are to machine at their highest accuracy, they must be operated at a constant spindle rpm. Future lathes purchased for this work should have the necessary stability for variable spindle speed operation.
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