Is there a relatively inexpensive method of Calibrating our Torque Wrenches?

[hogheavenfarm]

We are a small metal manufacturing shop looking to bring some of our external calibration jobs in house. Is there a relatively inexpensive method of calibrating our torque wrenches available? We do not need high accuracy, but we do need it NIST traceable. What would your suggestions be?
We have about 50 various size torque wrenches and drivers, and I am not able to keep our torque equipment on a schedule since we are largely contract driven, and when the jobs slow down, so does the calibration budget. I end up removing most of the tools from use until the next job comes along. Then we are up against it timewise to send the wrenches out and get started on the job. I can stay ahead on the mics and calipers simply because I can do them here while it is slow.

 

[BradM]

Hmm... good question.

It depends on a number of factors. First, are all the torque devices in a similar range? Do you have a lot of variance of ranges (oz/in; inch/lbs; etc.)

We do not need high accuracy

I understand what you mean, but the required accuracy and gaining the appropriate ratios is important. If you end up with a 1:1 ratio, you might as well flip a coin. So, the accuracy of the instruments you have would need to be assessed. This will assure that you get an appropriate standard with sufficient accuracy.

I see a couple of ways to calibrate in-house. First, get a test rig with weights to verify your torque instrument. Or, get an instrument with sufficiently higher torque accuracy, and use it to check your shop instruments. With this setup, you will need to build a jig and assure that you have minimized additional factors like offset addiing to torque, etc.

Do you have enough history on them that you could extend the calibration interval?

On the surface, unless you have a lot of in-house torque equipment, I'm not sure you would get a payback quick enough to justify carrying it in-house.

 

[WestCoastCal]

I may have misinterpreted what you wrote, but when you stated that you can't keep them on an schedule, it sounds like they get calibrated if there is new contract. When properly managed, the cal due date is when the instrument should (theoretically) go out of its MPE.
What you torqued with the torque wrenches have not been validated until the torque wrenches have been recalibrated. If in tolerance, there is a higher probability of what you torqued being good. If the torque wrench tested out of tolerance, there is a higher probability of what you torqued as not being good.
I agree with Brad, doing them in house will cost a nice chunk to get up and running (let alone the quality management system requirements). Also, if you have past history, do an interval analysis to see if you have the intervals set properly. Lastly, if you can determine what accuracy you actually require, then you can definately dictate to your vendor as to what the acceptance criteria should be going forward. (they should base the as found condition on the previous calibrated accuracy prior to derating).

 

[BradM]

Oops! I must correct myself. You do not "calibrate" a torque wrench. You determine it's capability:

http://elsmar.com/Forums/showpost.php?p=376473&postcount=2

Sorry Miner.

 

[hogheavenfarm]

Thanks Brad and WestCoast, (and Miner),
yes, we have inch pounchs and ft pounds - I only mentioned accuracy since I saw that the calibration equipment was sold to varying levels of accuracy , I meant to say we needed to lowest level for our work generally -

As for calibration interval - you are again correct , there is no check until the equipment is calibrated again. Unfortunately I have no control over this, nor is any of this understood in this organization. But thats getting in too deep for this question....
Calibration records exist, scattered though they are, and the equipment is scheduled for annual calibration, although in many cases it should be at 6 months due to heavy usage. Again, I have no say in this matter. I am currently sending out wrenches that are past calibration by over two years. Some is due to equipment being used off site, and that equipment is only returned at the completion of the job, regardless of whether is expires in the meantime.
Calibration here is seen only as an expense to be charged to the start of a job, because it is a prerequisite of the customer, not that its good business practice.

 

[AndyN]

Oops! I must correct myself. You do not "calibrate" a torque wrench. You determine it's capability:

http://elsmar.com/Forums/showpost.php?p=376473&postcount=2

Sorry Miner.

Indeed, Brad! This is another one legends which grew in reaction to an auditors questions...

I had experience of a shop who did little but assemble large equipment using bolts. They found, through capability studies of their wrenches, that the more expensive (initial price) torque wrenches (breaking beam type) were far more capable than lower cost or dial indicator types. As a result of the initially expensive (daily-weekly) studies, checking wrenches could be backed off to a monthly event etc.
The torque setting master(s) were in the regular calibration program, of course...

 

[JaxQC]

Google the words “torque analyzer”. Send it out to get it calibrated to NIST standards. Then do all the rest yourself at your shop.

Remember to check it across the range (linearity) ie… 30, 60, 90 for a 100 wrench & not just one location. Also add it to your Lab Scope.

Ballpark is @ $ 1500.

 

[tamale]

Try this!

http://http://www.torqueleader.com/news/qtc-12-new-to-the-qtc-range/

Tamale