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% Gauge R&R or Precision-to-Tolerance ratio

Feb 27, 2019 6:28 PM
(3843 views)

When reporting the Gauge R&R in version 13.1.0 the below report is available. When I open help, the below does not specify which is the % Gauge R&R number for the guidelines.

Example of the Gauge R&R Report

Note: To generate the reduced Gauge R&R report, select File > Preferences > Platforms > Variability Chart > Reduced Gauge RR Report.

In this example, the values in the Variation column are the square roots of sums of variance components scaled by the value of k (6 in this example).

Acceptable Percent Measurement Variation shows guidelines for measurement variation, as suggested by Barrentine (1991).

Acceptable Percent Measurement Variation

< 10% | excellent |

11% to 20% | adequate |

21% to 30% | marginally acceptable |

> 30% | unacceptable |

Note the following:

• If you have provided a Tolerance Interval in the Enter/Verify Gauge R&R Specifications window, a % of Tolerance column appears in the Gauge R&R report. This column is computed as 100*(Variation/Tolerance). Also, a Precision-to-Tolerance ratio appears at the bottom of the report. This ratio represents the proportion of the tolerance or capability interval that is lost due to gauge variability.

• If you have provided a Historical Sigma in the Enter/Verify Gauge R&R Specifications window, a % Process column appears in the Gauge R&R report. This column is defined as follows: 100*(Variation/(K*Historical Sigma)).

• The Number of Distinct Categories (NDC) is defined as (1.41*(PV/RR)), rounded down to the nearest integer.

Below are my results. If I use the 3.4% Gauge R&R then I believe my MSA is Excellant.

But if I look at the .81 Precision to Tolerance Ratio my MSA is not good as I would read this as 81%. Which is the correct number to use for the above guidelines?

Gauge R&R (copied as Text)

Measurement Source Variation (6*StdDev) % of Tolerance which is 6*sqrt of

Repeatability (EV) 0.0779517 77.95 Equipment Variation V(Within)

Reproducibility (AV) 0.0221650 22.17 Appraiser Variation V(Technician)

Technician 0.0221650 22.17 V(Technician)

Gauge R&R (RR) 0.0810417 81.04 Measurement Variation V(Within) + V(Technician)

Part Variation (PV) 2.3527216 2352.7 Part Variation V(Part SN)

Total Variation (TV) 2.3541170 2354.1 Total Variation V(Within) + V(Technician) + V(Part SN)

6 k

3.44255 % Gauge R&R = 100*(RR/TV)

0.03445 Precision to Part Variation = RR/PV

40 Number of Distinct Categories = 1.41(PV/RR)

0.1 Tolerance = USL-LSL

0.81042 Precision/Tolerance Ratio = RR/(USL-LSL)

Using last column 'Part SN' for Part.

Variance Components for Gauge R&R

Component Var Component % of Total

Gauge R&R 0.00018244 0.12

Repeatability 0.00016879 0.11

Reproducibility 0.00001365 0.0089

Part-to-Part 0.15375831 99.88 +++++++++

2 REPLIES 2

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Re: % Gauge R&R or Precision-to-Tolerance ratio

Dear @caroljackson ,

I would like too introduce you to my friend Donald Wheeler. (I think of him as a friend, he likely has not idea who I am).

I could restate the problem as he puts it, or just post the paper here: https://www.spcpress.com/pdf/DJW189.pdf

The proportions, following the AIAG procedure, which JMP follows exactly, aren't really proportions. So it's possible to have both good, marginal and acceptable results simultaneously.

I highly recommend reading the paper in the link; however, you can't un-know the problem if you do, so read it at the peril of your bliss.

Best regards,

Byron

JMP Systems Engineer, Pharm and BioPharm Sciences

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Re: % Gauge R&R or Precision-to-Tolerance ratio

Ans to add to Byron's suggestion, get Wheeler and Lyday's book Evaluating the Measurement Process.

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