A production-sized, externally pressurized and air-lubricated spindle, capable of supporting 400-pound cantilevered loads, was fabricated for use in a program de¬signed to improve the accuracy of a Heald 15 by 15-inch numerically controlled turning and boring machine tool. Heat generation in the precision ball bearings of the original spindle gave indications of being a significant source of inaccuracy in parts machined on the lathe. Because of the low friction and subsequent low heat-generation characteristics of the air bearing, the spindle was successfully used to reduce the associated errors, while providing improved rotational accuracy.
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