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Narrow limit gauging

Bill Levinson

Industrial Statistician and Trainer
I am trying to determine if there is a widespread interest in narrow limit gauging, in which you compress the acceptance limits for a go/no-go gage that can be set to a specific dimension (e.g. with gauge blocks). This can reduce your required sample enormously (e.g. an ANSI/ASQ Z1.4 plan whose single sample is 1250 can be converted into a plan whose sample size is less than 50) but it does have prerequisites:

(1) The critical to quality characteristic must follow a normal distribution.
(2) It must be measurable in terms of real number data (to obtain an estimate of the process standard deviation)
(3) The go/no-go gage must be adjustable to a specific real number (e.g. mils)
(4) Increases in the nonconforming fraction must result from a shift in the process mean, as opposed to an increase in process variation--otherwise the underlying assumptions don't work.

When these assumptions are met, however, we can get some VERY nice plans whose OC curves are almost identical to those of the original ANSI/ASQ Z1.4 plans but with much smaller sample sizes.

I got the idea from Anthony Chirico's article Applying the Procedures of MIL-STD-105 to Imaginary Limits | Quality Digest

and looked up Schilling's approach to get this: How to Convert ANSI/ASQ Z1.4 Sampling Plans Into Narrow-Limit Gauging Plans | Quality Digest


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