Gage Calibration, Repeatability, and Reproducibility

Feb. 4, 2009 - PRLog -- Gage calibration is the foundation of a quality program. Making sure that measuring instruments are properly calibrated is critical to quality manufacturing operations. A gage that doesn't read accurately, and repeatably will compromise the integrity of quality control systems.

Gage calibration is only the first step to gage integrity. A well calibrated gage can give an accurate reading but without gage repeatability and reproducibility, there is no guarantee that a second or third measurement will be the same. A quality control department's reputation is based on their ability to prove, duplicate, and defend manufacturing dimensional data.

The number one problem in evaluating a gage design is understanding the design influences, sample part conditions, and location methods that affect the success of a gage passing a GR&R study.

Gage Repeatability and Reproducibility (GR&R) studies provide information on measurement system performance by using ratios of measurement variation and part tolerance gathered from multiple part and operator measurements. If measurement variation can be reduced and GR&R ratios improved, it is easier to differentiate between parts that are in or out of specification, allowing parts to be accepted or rejected with greater confidence.

In GR&R studies, several ratios are calculated. Two of the most important ratios are measurement variation to part tolerance and measurement variation to total variation.

The first ratio, the ratio of measurement variation to part tolerance, represents how well it can be determined whether a part is in specification. If the measurement error is too large, poor parts will be accepted and good parts rejected.

One very critical component in the design of a gage is to study the location points; where the part will rest in the gage. Even the condition of the surface of those location points on a part can have devastating results when GR&R is performed. Surface finish and softness of a contact surface of a part can cause wear between checks and change the orientation and location of the measured dimension. This means that the gage integrity is related to the quality of contact surfaces on the individual parts. Even dust, dirt, coolant, and other impurities will affect the performance of the gage. A lack of understanding behind the math of a GR&R and what influences data can result in a poorly designed gage.

Birdsall Tool & Gage (http://www.birdsalltool.com) has years of experience, a gage library unmatched in the industry, and the courage to speak clearly with a client who wants to implement best gage practices and reduce the total cost of gaging while enhancing the reputation of the customer's quality control department.

Birdsall Tool & Gage Co. designs and builds fixture gages, fixed gages, inspection and gaging accessories, ring gages, plug gages, thread gages, snap gages, electronic gages, mechanical gages, data collection gages, masters and setting gages, CMM fixtures, special tools and tooling with customer satisfaction in mind. Call 248-474-5150 us for more information about our company.

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Birdsall Tool and Gage Co. designs and builds fixture gages, fixed gages, inspection and gaging accessories, ring gages, plug gages, thread gages, snap gages, electronic gages, mechanical gages, data collection gages, masters and setting gages.