Narrow Limit Gauging
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Speaker : WILLIAM LEVINSON
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When : Tuesday, June 10, 2025
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Time : 01 : 00 PM EST
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William A. Levinson, P.E., FASQ, CFPIM is the principal of Levinson Productivity Systems, P.C. He is an ASQ Certified Quality Engineer, Quality Auditor, Quality Manager, Reliability Engineer, and Six Sigma Black Belt, and the author of several books on quality, productivity, and management.
Narrow limit gauging, which relies on tightened acceptance limits to assess the quality of a sample, can reduce enormously the required sample size and therefore the cost of inspection. This webinar will equip attendees to convert any ANSI/ASQ Z1.4 (formerly MIL-STD 105) sampling plan into a narrow limit gauging plan.
Learning Objectives
- A review of the basics of ANSI/ASQ Z1.4. A major takeaway is that to ensure very high quality levels (very low acceptable quality levels on the order of 0.01% nonconforming), extremely large sample sizes, on the order of 1250 pieces, are required. Although double, multiple, and sequential sampling plans can reduce the average sample number, narrow limit Gauging is far more effective.
- When the following conditions are met, narrow limit gauging, which tightens acceptance tolerances for the purpose of deciding whether to accept or reject a production lot, can be used.
- The quality characteristic must follow the normal (bell curve) distribution, and it must be possible to quantify its standard deviation (e.g. with instruments that return variables or real-number data).
- Go/no go gages must be capable of accepting or rejecting parts on the basis of real number specifications. As an example, the gages might be set to accept or reject work by means of gage blocks.
- Increases in the nonconforming fraction must be due entirely to changes in the process mean (as opposed to process variation or other causes). - If the above conditions are met, then the acceptance limits (for the purpose of deciding whether to accept or reject the lot) are compressed by t standard deviations as previously measured. The result is a narrow limit gauging plan whose sample size is considerably smaller than that of the original ANSI/ASQ Z1.4 plan.
- Note that otherwise conforming parts are not rejected by the tightened limit. The objective is to accept or reject the lot based on a much smaller sample size. - The operating characteristic (OC) curves of the original sampling plan and the narrow limit gauging plan can be plotted side by side to show the customer that the latter plan provides as much protection against poor quality as the original.
Who Should Attend
Quality managers, engineers, technicians, and practitioners with responsibility for attribute (pass/fail) inspections for which go/no-go gages can be set for quantitative acceptance limits.
Topic Background
Narrow limit gauging is described by Schilling, Edward. 1982. Acceptance Sampling in Quality Control. New York: Marcel Dekker. Modern software makes deployment of these plans to the shop floor much easier.
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$199.00
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