Flatness Change of Vacuum Chuck Surface for Ultra-Precision Turning by Elastic and Thermal Deformations

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Temperature increase and flatness change of vacuum chuck surface on ultra-precision lathe with hydrostatic oil spindle are analyzed. 1.The surface shows nearly uniform temperature increase (max.7.5ﾟC, at 3000rpm) due to the heat generated by the spindle rotation. 2.Increase in the centrifugal force causes a concave deformation of the surface. (0.265mu m, at 3000 rpm) 3.Probe traversing method is proposed to analyze the flatness change precisely. Thermal deformation due to the spindle rotation changes the surface to a convex profile. Flatness change of the surface is max. 1.9 mu m (at 2000 rpm) - 2.8 mu m (at 3000rpm) . 4.Considering uniform temperature distribution the convex deformation is caused by the structure that the chuck is fastened at the outer portion with steel bolts of which thermal expansion coefficient is less than that of aluminum chuck.And characteristics of hydrostatic air spindle are analyzed. 5.Static imbalance in appearance is caused when the spindle is stopped by braking with direct current. Statical balancing procedure under this state decreases the rotational accuracy of spindle at high speed operation. This imbalance disappears by free-run stopping of spindle. 6.Maximum static friction moment of the spindle is nearly 30mm*2gf. 7.Amount of the spindle shrink caused by centrifugal force is 3.0mu m (at 7000rpm, 695 mm total length) . 8.Amount of the spindle expansion caused by centrifugal force is 0.3mu m (at 7000rpm, 60mm diameter).