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Torque Wrench Calibration Tolerances.

Discussion in 'IATF 16949:2016 - Automotive Quality Systems' started by S1D3K1CK, Jun 9, 2020.

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  1. S1D3K1CK

    S1D3K1CK Active Member

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    I have a total of 5 torque wrenches and we have them sent to an accredited lab (A2LA) for calibration. My question is, how often is calibration required and what tolerances are allowed? The lab rejected 2 this year and the 2 they rejected HAVE NOT been used since last calibration from the same company. Their explanation is "the tools are cheap and the "clicking" mechanism inside tends to wear out even if the tools are stored properly because the tools are such a cheap brand" We have to follow automotive guidelines (IATF and ISO standards) to calibrate and use of measurement equipment. We also have torque values required by the customer, depending on which installment is required, that the customer has set in place. The calibration company has suggested we "open the tolerance" on the rejected torque wrenches. I have no idea on what that is supposed to mean because we never set the tolerance. If they open the tolerance, would that no longer be an accredited calibration as it states in the IATF requirements? How would I explain that to an auditor if we go that route? Or what steps should be taken to resolve this?
     
    S1D3K1CK, Jun 9, 2020
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  2. Andy Nichols

    Andy Nichols Moderator Staff Member

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    Calibration for such devices is a matter of gathering data and analysis. Experience shows that, in general terms, the more a TW costs, the better it performs. However, in essence, it's about the amount of use they get. You're probably spending a lot of money sending them to a lab, so you may find that, in the long run, getting a torque setting master and checking your own as frequently as you want to, to generate the stability data, is the lower cost and more effective way to go. https://www.mscdirect.com/product/details/46068870 (no affiliation)

    ISO 6789 might help on tolerances etc. At the end of it all, it's the tolerance you agree with the client for that type of fastener.

    The lab isn't affected in any way. You can use whatever tolerance bands you wish. The lab is simply there to report how your wrenches performed. Auditors may not understand what they are being told, so you have to be convinced (and have data) to support your approach. (Good luck with that)

    Recommendation? Buy a torque setting master, get it calibrated, do "verifications" of your torque wrenches on a regular basis (daily, weekly, monthly as you see fit to support production) and look at the data graphs for trends. I've seen Snap-On wrenches go for 5+ years, being used daily on 25mm dia bolts and they didn't need cal. The data is what you need.
     
    Andy Nichols, Jun 9, 2020
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  3. S1D3K1CK

    S1D3K1CK Active Member

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    Our company is order driven so the use of the torque wrenches are sporadic. I think the best option is to get us a torque tester and have that calibrated as you suggested. As for starting that I will have a lot of research to do haha. As per IATF, I haven't found certified calibration company locally so I will have to research the manufacturer we purchase from. Thanks for the info
     
    S1D3K1CK, Jun 9, 2020
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  4. Andy Nichols

    Andy Nichols Moderator Staff Member

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    For sure. You won't have to do it often, so if they're not local, no biggie. You might find there's a lab which provides their services out of a van, so they may be several states away, but in fact right down the road... (BTW you want an "accredited" lab, not "certified")
     
    Andy Nichols, Jun 9, 2020
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