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/similar gauges:
Conservative approach: Same brand and model of gauge
Alternate approach: Similar gauges (brand or model not relevant)
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:
Perform the MSA and associate it with the gauge family record.
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
- 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
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)
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
- 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
Perform the MSA and associate it with the gauge family record.
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