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Torque Wrench Calibration Frequency (Calibration Interval)

#21
Re: Calibration Frequency of Torque Wrenches

Is this engines or overhead doors? Marilyn said some aren't even used once a year. It doesn't sound like they need that many, but if they do, in-house calibration sounds like a good idea to me.
Good point - I missed the reference back to the OP, however, the principle is still good!;)
 

Terry

Involved In Discussions
#22
Re: Calibration Frequency of Torque Wrenches

our calibration procedure define calibration interval 3 months, of course, our company just establish a in house calibration lab in order to save money. all calibration interval time depends on the product and the frenquecy of use, product quality and customer statisfaction is our forever objective.
 
S

steviet

#23
Re: Calibration Frequency of Torque Wrenches

Just remember the longer the re-calibration period the more work you may have to recall if there is a problem. Mind you with the changes to the British standard coming in the calibration uncertainties will be that high makes you wonder whats the point. And thats when its done properly
 

dgriffith

Quite Involved in Discussions
#24
Re: Calibration Frequency of Torque Wrenches

Simplistically, you could use the torque master as a check standard and perform daily, weekly, or monthly checks and just track measured values over time. This at least would allow you to develop a trend for each torque wrench during the calibration interval. Masters are not that expensive compared to the cost of litigation when one or seven overstretched bolt(s) finally snap under stress and the left half of the door falls on something or someone. And don't say never, because it never happens until it happens to you.

PS, are your technicians properly trained to use the different types of wrenches? Using a calibrated torque wrench incorrectly can be as bad as using an un-calibrated wrench correctly. You're guessing hoping praying assuming the number is correct.
 

IATFuser

Starting to get Involved
#25
Hi,

We have an assembly operation where we use preset torque wrenches for tightening the screws. We set it at 80 inch LB. But we do not know what should be the tolerance on the setting. We verify the preset torque everyday before use by using Torque watch. But the wrench that is set at 80 inchLB shows data from 70-98 inchLB. Is there a standard tolerance for wrenches? Because the certificate from the manufacturer says +/-4% accuracy. Then are our gauges out of calibration?
 

dgriffith

Quite Involved in Discussions
#26
I am not familiar with TorqueWatch, so I do not know the method of measurement.
4% of 80 is 3.2; some torque presets (like drivers and microwave connector wrenches) are 6%, so 4.8. Anything over 85 or under 75 would normally suggest out of tolerance, but there are other factors--especially human. I recommend getting it calibrated at a reputable vendor (here in SoCal a good vendor will charge 75 bucks or so) and then keep track of user measurements to look for trends. There are several process control methods available here that might help, but first ensure your wrench is in fact in tolerance. Make sure you get as-found and as-left data with the calibration.
 

IATFuser

Starting to get Involved
#27
Hi @dgriffith Thank you!

But the accuracy on the certificate from the manufacturer+/-4%, is it the tolerance? Torque watch(may be that is our terminology) is Torque Tester . We verify the preset torque everyday before using the wrenches on the torque tester. And the wrenches are within the calibration due date.
 
#28
Hi @dgriffith Thank you!

But the accuracy on the certificate from the manufacturer+/-4%, is it the tolerance? Torque watch(may be that is our terminology) is Torque Tester . We verify the preset torque everyday before using the wrenches on the torque tester. And the wrenches are within the calibration due date.
Great to see people verifying the torque devices prior to use. That's the right way to do it!
I might suggest checking at the end of the day as well. That way you will know if it went bad during that shift and can start to assess any possible impact on your products.
I assume that the tool user is the one who verifies the accuracy. That is important.
I also assume that you are logging the test results, in case you need to assure the tool was good on a given day.
And I assume that the torque tester is also calibrated and within the calibration date.

The 4% accuracy on the certificate is a very typical number, so you can assume that is the tolerance.
Your readings between 70 to 98 are very problematic. The tolerance would be ±3.2 in-lb.
Are these readings for one particular tool, or for multiple tools? One tool user or multiple users?
 

IATFuser

Starting to get Involved
#29
Thank you @dwperron !

Yes the shift leader verifies the torque for the preset wrenches with the torque tester. We have multiple wrenches in use and all of them are verified everyday. However like I said, we did not have the tolerance set up. The torque tester is within the calibration and the frequency is yearly.
We have 3-4 assembly operators (users) using these wrenches. Like you said +/-3.2 in-lb looks very difficult for us based on the historical data.
Checking the torque at the end of the day is a very good suggestion.

Can we set out own tolerance based on the product requirement?
 

dgriffith

Quite Involved in Discussions
#30
Yes, you can set your own process tolerance independent of the tool, but an inspector might take issue with using an out of spec tool regardless of process requirements.
The 4% (3.2 lb-in in this case) is the tolerance for the wrench. Your process/product requirements should dictate what the accuracy of a calibrated tool or instrument must be.
If your process only requires ±8% of required torque (torque screw to (80±6.4) lb-in) then you need a tool that meets that requirement.
 
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