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Intro to MSA of Continuous Data - Part 10: Creating gauge families

Miner

Forum Moderator
Staff member
Admin
#1
This is the tenth in a series of articles about MSA. The focus of this article will be on minimizing the number of MSA studies by creating families of gauges.

A frequent question in the Cove is: “Must I perform an MSA on every gauge/part combination?” The answer is: “No. You may create families of gauges, and perform MSA studies by family.”

Wait! Not so fast! What constitutes a family of gauges? Well, there are certain criteria that must be met:
  • Same gauges
  • Same product characteristics
  • Same tolerances or process variation depending on use of gauge
Another, less restrictive approach that could be used:
  • Similar gauges
  • Similar product characteristics
  • State the smallest tolerance or process variation (standard deviation) that the gage family may be used to measure and still achieve an acceptable R&R result
Let’s cover each of these in more depth:

Same/similar gauges:
Conservative approach: Same brand and model of gauge

Alternate approach: Similar gauges (brand or model not relevant)
  • Same type (e.g., calipers, micrometers, 3 – point bore gage, etc.);
  • Same range (e.g., 0 – 6 inch, 0 – 12 inch, etc);
  • Same display (e.g., digital, dial, vernier, etc.);
  • Same resolution (e.g., 0.0001, 0.05, etc.)
  • Same technology, if relevant (e.g., scaled, rack and pinion gear, electrostatic capacitance technologies for calipers)
  • Same anvils, if relevant (e.g., outside, inside, step anvils for calipers)
Same/similar product characteristics:
Conservative approach: Same features

Alternate approach: Similar features (e.g., diameter, width, step etc.) within a specified range. Be cautious when establishing the range. You may need to perform a series of MSAs to establish how large this range may be. The impact of size will usually manifest itself through changes in the within-part variation, or by affecting the ease with which an operator can handle the part and gauge together.

Same tolerances or process variation:
Conservative approach:
  • Same tolerance if gauges are used for inspection
  • Same process variation if gauges are used for SPC
Alternate approach:
  • If gauges are used for inspection, state the smallest tolerance at which an acceptable % Tolerance may still be achieved
  • If gauges are used for SPC, state the smallest process variation standard deviation at which an acceptable % Study Variation may still be achieved
Once you have created a gauge family, document it. Create a record for each gauge family that clearly describes the gauges, characteristic and size range. The gauges could be identified by listing all serial numbers, gauge calibration ID numbers, or by clearly specifying the type, range, display, resolution and anvils.

Perform the MSA and associate it with the gauge family record.
 
Last edited by a moderator:
D

Dean Frederickson

#5
Could I please get some help trying to understand our customer needs. they asked for a gage R and R. We gave it to them. they are o.k. with the 16.16 %R&R but not the 89.27 % apprasier variation.
% process var. % tolerance var.
% Equipmeny variation 32.82 5.58
% Appraiser variation 89.27 15.17
% R & R 95.11 16.16
% Part variation 30.88 5.25

I will be the 1st to admit I do not know how to read these results can anyone enlighten me?
 
G

Guest

#7
I have been using families of gages in the past and never was questioned about it but now I'm wondering if there is a note on MSA or any other AIAG document that specifically mentions and allows this, is there any?
 
G

Guest

#8
thank you for sharing your knowledge with us. one question will be , is there any document or rule that says we can do this Family groups because during the audits I am sure the auditor is gong to question this procedure and I would like to have probe that this is permitted.

thank you
 

Miner

Forum Moderator
Staff member
Admin
#9
Gage families are not specifically called out, but throughout the AIAG MSA manual, chapter 1, particularly section C, it states to use COMMON SENSE during planning. This is no guarantee, but will work with most auditors.
 
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