How would one calculate pitch diameter for external threads on a CMM and verify that the results are correct. I need to check some pretty large acme threads im not too sure about the nominal dimensions.
When measuring internal threads we suggest setting the "pitch" in the "auto circle or cylinder" you are measuring to the thread helical path pitch (i.e. 1/4 20 thd = pitch of 0.050) you will find the button within the auto feature, (the last frame on the bottom)... At least this will find the center of the thread regardless of hitting the minor diameter start position... That is why it is there...for a more accurate measurement of location the make snap spring loaded internal thread balls and cylinders you can purchase (rather expensive though) for each location... The writer suggests using the pitch box though... Very repeatable... at least if it does not hit the minor diam it hits the same location for the circle.
When measuring internal threads we suggest setting the "pitch" in the "auto circle or cylinder" you are measuring to the thread helical path pitch (i.e. 1/4 20 thd = pitch of 0.050) you will find the button within the auto feature, (the last frame on the bottom)... At least this will find the center of the thread regardless of hitting the minor diameter start position... That is why it is there...for a more accurate measurement of location the make snap spring loaded internal thread balls and cylinders you can purchase (rather expensive though) for each location... The writer suggests using the pitch box though... Very repeatable... at least if it does not hit the minor diam it hits the same location for the circle.
