Position measuring method for reference surface

1. A position measuring method of measuring, by a probe, a position of a reference surface of a workpiece that is supported by a fixing tool when the workpiece is machined, the position measuring method comprising:

bringing the probe into contact with the reference surface at a plurality of different positions, and measuring a height of the reference surface; and

setting a position at which the height of the reference surface is largest, as the position of the reference surface.

2. The position measuring method according to claim 1 , wherein the different positions at which the probe is brought into contact with the reference surface are set based on a distance from a support center position at the reference surface supported by the fixing tool.

3. The position measuring method according to claim 2 , wherein the different positions are set to positions symmetrical with respect to the support center position.

4. The position measuring method according to claim 1 , wherein the set position of the reference surface is used to measure a machining position that is apart from the reference surface.

5. The position measuring method according to claim 4 , wherein a hole having an axis substantially parallel to the reference surface is formed at the machining position.

6. The position measuring method according to claim 1 , wherein the height of the reference surface is a position of the reference surface in a direction perpendicular to the reference surface when the reference surface has no asperities.