Early machines used a simple chart recorder to graph roundness. Current machines use dedicated processors or computers to monitor and analyze the gage head signal. Modern electronics have made the inspection process simple and comprehensive, but the heart of a roundness machine remains in the precision spindle. Roundness errors in the spindle have the greatest influence on the measurement results. Most equipment manufacturers offer roundness machines with spindle deviations less than 0.000003 in.
Spindles can run on either air or mechanical bearings.
Air-bearing spindles are typically less expensive than mechanical bearings in the same accuracy range but require connection to an air supply and regular maintenance. Care must be taken to ensure that the air supply is clean, dry, and of constant pressure. Moisture or dirt will contaminate the bearing and can lead to failure. Dynamic-load capacity is another factor to consider. Be sure to select a spindle that will support the weight of the parts you intend to measure.