SPINDLE THERMAL DRIFT MEASUREMENT USING THE LASER BALL BAR

Thermally induced errors are major contributors to the overall accurac y of machine fools. An important component of thermally induced errors is the error associated with spindle thermal drifts. In this paper, a novel method is developed to measure spindle thermal drifts in machin e fools using a laser ball bar (LBB) as the calibration instrument. Th e method is implemented on a two-axis CNC fuming center. The LBB is us ed to measure the coordinates of the spindle center and the direction cosines of the spindle axis at various thermal states. The axial, radi al, and tilt thermal drifts of the spindle are then computed from the changes in these coordinates. The new method is verified by comparing the spindle drifts measured with the LBB to those measured by capacita nce gauges. The results obtained by the new method show good agreement with the capacitance gauge technique. The primary advantage of the ne w method is the ability to measure the spatial coordinates of the spin dle center and direction cosines of the spindle axis with the same ins trument used for measurement of the geometric errors of the machine ax es.