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  Measurement, Test and Calibration
  Gage R & R on torque wrenches

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Author Topic:   Gage R & R on torque wrenches
posted 07 July 2000 04:09 PM           Edit/Delete Message   Reply w/Quote
Has any one out there established a method to conduct R & R on digital torque wrenches
We currently use 5-50 nM range units with datastats to take static torque readings on joints secured with electric nut runners connected through focus boxes. Our last audit produced a minor for not having MSA on these wrenches. Any help or suggestions would be appreciated

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posted 11 July 2000 07:57 PM           Edit/Delete Message   Reply w/Quote
Suppliers of these devices have masters that they work to that are traceable to a master standard. We have a master and a back-up that are sent out for calibrtion on a quarterly basis. The wrenches and masters go through the same MSA standards for Bias,lineariy,and stability on a pre-defined basis.

In my opinion the best method is to establish stability through the use of a weekly check documented on a variables chart (X-R Sample 5)

The bottom line is to define the need for a master during the APQP process and hold your approved suppliers to the conditions set forth in the contact.

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Brian Dowsett
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Posts: 35
From:Waterford, Ireland
Registered: Nov 1999

posted 13 July 2000 04:28 AM     Click Here to See the Profile for Brian Dowsett   Click Here to Email Brian Dowsett     Edit/Delete Message   Reply w/Quote
I am assuming that when you quote "static torque" you are applying torque in the tightening direction until the joint starts to rotate again, at which point the inspector either takes a reading based on feel, or in some cases the electronic torque wrench can sense the movement.
I had a similar problem a few years back, in that to do a conventional R&R it is necessary to keep measuring the same joint, but each time you measure it, by the nature of the check, it has got a little tighter.
As the first answer suggests, you can use a master gauge (probably digital) and do your ten repetitions against this with each inspector. The drawback with this method is that it does not simulate the real life use of the gauge, in that the inspector will apply torque until the master reaches a predefined reading and then stop - there is no "feel" involved. As you know, the main source of variation in this type of measurement is that one insector will gently apply torque to a joint and get a fairly true reading, whilst an untrained fella will "swing" on the wrench and get a shock value a lot higher.
Our approach was to build a rig, with a centrally mounted wheel (with a square drive) from which a cable supported a platten, on which we could put dead weights. Therefore we could calculate the true torque from the weight x dia of the wheel.
The inspectors then did the R&R on this rig, at typical torque settings for the application. This gave a much better simulation of the actual gauge use, where an accurate reading still depended on the inspectors "feel" of when he overcame the friction in the rig and got the weight moving (we made sure he could not see the weight).
This not only got us through the audit problem but more importantly gave us a good training method on how to use a torque indicating wrench properly.

Hope this of some help.


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