Rotary table and roundness measuring apparatus

A roundness measuring apparatus comprising:

• a rotary table comprising:
• a rotary disk that is rotatable around a vertical rotation axis;
• a stator assembly comprising a bearing that supports the rotary disk such that the rotary disk is freely rotatable;
• a slide disk that is slidable on a top surface of the rotary disk;
• a position adjustment bracket that displaces the slide disk along the top surface of the rotary disk;
• a placement disk supported by the slide disk;
• a plurality of air nozzles arranged on a top surface of the bearing in an annular configuration concentric with the rotation axis, and forming a static pressure air film between the top surface of the bearing and a bottom surface of the rotary disk;
• an aerostatic pocket positioned between the top surface of the rotary disk and a bottom surface of the slide disk;
• and
• a communication aperture formed in the rotary disk, the communication aperture configured to introduce pressure of the static pressure air film into the aerostatic pocket.