Measurement Systems Analysis Fundamentals
Determine the number of appraisers, number of sample parts, and the number of repeat readings. Larger numbers of parts and repeat readings give results with a higher confidence level, but the numbers should be balanced against the time, cost, and disruption involved.
Use appraisers who normally perform the measurement and who are familiar with the equipment and procedures.
Make sure there is a set, documented measurement procedure that is followed by all appraisers.
Select the sample parts to represent the entire process spread. This is a critical point. If the process spread is not fully represented, the degree of measurement error may be overstated.
If applicable, mark the exact measurement location on each part to minimize the impact of within-part variation (e.g. out-of-round).
Ensure that the measurement device has adequate discrimination/resolution, as discussed in the Requirements section.
Parts should be numbered, and the measurements should be taken in random order so that the appraisers do not know the number assigned to each part or any previous measurement value for that part. A third party should record the measurements, the appraiser, the trial number, and the number for each part on a table.
Repeatability and Reproducibility Assessment (Gage R&R):
This discussion refers to the data collection sheet sample that follows as Figure 2. You can download the data collection and analysis spreadsheet at the end of this section. Follow the steps below to conduct a Gage R&R study:
Determine the number of appraisers, trials, and parts, which may vary from study to study. A rule of thumb is 2-3 appraisers, 2-3 trials, and 5-10 parts - with 10 being greatly preferred. The downloadable MoreSteam.com spreadsheet will accommodate any combination within this range. In this example we will use 2 appraisers, 3 trials, and 10 parts.
Identify three appraisers who are all trained in the proper measurement procedure and identify them as A, B & C.
Fill in the yellow blanks at the top of the form with the required background information (Gage Type, Date, etc.). Also fill in the blank at the bottom of the form asking for the total specification tolerance.
Collect ten parts that represents the range of process variation. If the parts don't vary as much as the process, the gage error will be overstated.
Identify each part with a number 1-10 in such a way that the appraisers can not see the numbers as they take the measurements.
Start with Appraiser A and measure each of the ten parts in random order. A third party should record the results of the first trial in row A-1. Proceed to Appraisers B & C following the same process. Then repeat the process for trials two and three.