Q: I need information on performing a Gage R&R on a torque wrench. We are using the wrench to check customer parts.
A: For reference on both variable and attribute Gage R & R techniques, a good source is the Automotive Industry Action Group (AIAG) Measurement Systems Analysis (MSA) publication.
The traditional torque wrench is a “generate” device in the sense that it generates a torque to tighten or loosen a fastener (a nut or a bolt, etc.). So, in a strict sense, it is not a “measurement” device. Therefore, both preset and settable torque wrenches are set to a torque value and then used to tighten a fastener or loosen a fastener. When loosening a fastener, it will determine how much torque is required to loosen the fastener. Usually, the clockwise motion is for tightening and counterclockwise motion is for loosening in a torque wrench.
To conduct a variable Gage R & R study on a torque wrench, we would need a “measurement” device which would be a torque checker with a capability to register peak (or breaking) torque. Many such devices are commercially available and if a facility is using torque wrenches, it is a good idea to have one of these to verify performance of torque wrenches. Such a device is usually calibrated (ensure traceable accredited calibration) and provides reference for proper working of torque wrenches.
Now, one would conduct a Gage R&R study using the typical format:
- Two or more appraisers.
- 5 to 10 repeat measurements at a preset torque by each appraiser, replicated 2 to 3 or more times.
A word of caution on torque wrenches and setting up the Gage R&R:
- The measurement is operator dependent, so operators need to be trained on proper toque wrench usage techniques.
- Ensure that torque is set between every measurement in the settable torque wrench to simulate actual usage between repeated readings.
- Ensure the number of repeated reading and replicated readings are the same for all appraisers.
The templates for data collection are available in spreadsheet format from commercial providers. Alternatively, one can design the template from the MSA publication referenced. The data would be analyzed using the guidelines from the MSA publication.
Good luck with the Gage R&R! It is a very useful and worthwhile exercise in understanding your measurement process.
Dilip A Shah
ASQ CQE, CQA, CCT
President, E = mc3 Solutions
Chair, ASQ Measurement Quality Division (2012-2013)
Secretary and Member of the A2LA Board of Directors (2006-2014)
To learn more about this topic, visit ASQ’s website.