Reference fixture for roundness measuring instrument

A reference fixture for a roundness measuring instrument for acquiring origin information of the roundness measuring instrument that includes a workpiece rotary mechanism rotatable with a workpiece being set thereon and the detector having a sensor for measuring a surface profile of the workpiece, and calibrating a detector thereof, the reference fixture comprising:

• a mount provided on a top face of the workpiece rotary mechanism;
• a calibration master provided on a top face of the mount for calibrating the sensitivity of the detector by the sensor of the detector;
• a reference ball disposed above the calibration master for providing the origin information of the roundness measuring instrument by the sensor of the detector;
• and
• a holder provided on the calibration master to hold the reference ball,
• wherein the holder is formed in a dimension capable of measuring the reference ball by the detector in Z-axis direction representing an axis line direction of the calibration master and in X-axis direction orthogonal to the axis line.