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Calibration of thread gages

old crone
I am asked to calibrate shop floor ring and thread gages.
I don't think that the CMM is the device to use.
I propose that I have a calibrated set of ring and thread gages in the lab as masters.
And calibrate the floor ones with those.
But I am open to ideas.
  • My guess is that you and your lab are NOT accredited to do that work, they just don't want to pay to send them out and have it done correctly.

    Yeah, I would give that a big pass, especially if any thing checked/approved with them is a safety critical item, you could see jail time for something like that.
  • in reply to Matthew D. Hoedeman
    Left a job for that exact reason. I wasn't putting my name on the stuff.

    I looked at the old 'in-house' calibration data. They had ring gages calibrated using gage blocks and all kinds of other pencil-whipped BS. Didn't even try to make it look right. The look on my face when I realized almost nothing in the place was calibrated must have been something.
  • Send it out to an accredited lab. It will save you the headache, time, and money to fix it if an auditor were to catch you.
  • Before we had a CMM, were were looking for a way to calibrate/certify threaded ring gages. My boss arranged a meeting with a sales guy from mitutoyo and he was like, "yeah, CMM can calibrate threaded gages all day." We went to check out the Mic trac out of Houston and then visited mitutoyo show room and talked to a application engineer and he was like no. CMM shouldn't and can't be used to check threaded gages. He said the acceptable way is with threaded set plugs and we would probably have a hard time explaining to our customers and auditors that we use a CMM to calibrate gages. Sales guy happened to be off that day we visited and yeah, we didn't buy a CMM to check gages.

    We use the mic trac 4000 to check threaded plugs and threaded set plugs. Set plugs are then used to verify threaded ring gages and adjust if needed.
  • OD thread plug gages are something I calibrate at my shop:

    -Using a super-mic, measure the major diameters
    -Using pitch mic, measure the pitch diameters
    -Record the info in Gagetrak (get acceptance tolerances from certs from when we used to send them out)
  • I used to have to check the thread gages in my area using the 3 wire method. What a pita that was. ISO certified now, so off to the lab they go.
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