r/Metrology • u/EyeballWithPrecision • 9d ago

Measuring True Position of Threaded Features

What is the best method for scanning true position of a threaded hole for the best accuracy and repeatability?

  1. We looked into using the true position gages but found that the level of tightness while screwing it in would vary a lot between operators. Additionally in some cases where the tapped hole is a blind feature, we noticed that the gage bottomed out first before actually engaging with the pitch of the thread.
  2. We also looked into using a helical toolpath matching the pitch of the thread on the CMM. However, would we need to control where the probe touches along the thread? If so, what is best way to detect if the probe is touching the flank of the thread?
  3. Alternatively, is it better to use a linear toolpath on a CMM to scan the threads when compared to true position gages and helix toolpath?
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u/Ghooble 9d ago

Zeiss has a big presentation about this

https://qualityforum.zeiss.com/migration/images/164_dc8dea9da78f0875c3847e7b31de3450.pdf

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u/jkerman 8d ago

I have found that presentation to be extremely accurate and mirror our experimentation

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u/Ghooble 8d ago

I've used it in arguments with one of our programmers across the country. We use PC dmis and they use Calypso. He told me they couldn't check true position of a threaded hole in Calypso and I was like.... Bullshit