Roundness Tester Gage R and R Frustration - Tolerance range of 20 microns

C

Curtis317

#1
Our plant has very tight tolerances. Most parts have a tolerance range of 20 microns. Right now I am working on a GRR for a roundness tester. The results were poor:

%Study Var %Tolerance
Source StdDev (SD) (6 * SD) (%SV) (SV/Toler)
Total Gage R&R 1.26179 7.57075 95.69 75.71
Repeatability 1.19401 7.16404 90.55 71.64
Reproducibility 0.40800 2.44801 30.94 24.48
Operators 0.40800 2.44801 30.94 24.48
Part-To-Part 0.38291 2.29744 29.04 22.97
Total Variation 1.31861 7.91167 100.00 79.12

Granted most of the variation is in the equipment(repeatiblity). The measurement was for concentricity. The max is 10 microns. The measurements were from @ 0.25 to 3.5 microns.
The distinct categories are 1.

Okay so this says that a very expensive and precise piece of equipment is useless for measuring this characteristic?

Can anyone provide some thoughts or guidance on this?
 
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Jim Wynne

Staff member
Admin
#2
Our plant has very tight tolerances. Most parts have a tolerance range of 20 microns. Right now I am working on a GRR for a roundness tester. The results were poor:

%Study Var %Tolerance
Source StdDev (SD) (6 * SD) (%SV) (SV/Toler)
Total Gage R&R 1.26179 7.57075 95.69 75.71
Repeatability 1.19401 7.16404 90.55 71.64
Reproducibility 0.40800 2.44801 30.94 24.48
Operators 0.40800 2.44801 30.94 24.48
Part-To-Part 0.38291 2.29744 29.04 22.97
Total Variation 1.31861 7.91167 100.00 79.12

Granted most of the variation is in the equipment(repeatiblity). The measurement was for concentricity. The max is 10 microns. The measurements were from @ 0.25 to 3.5 microns.
The distinct categories are 1.

Okay so this says that a very expensive and precise piece of equipment is useless for measuring this characteristic?

Can anyone provide some thoughts or guidance on this?
I think the NDC (Number of Distinct Categories) result is the key. It appears that you have "fat" data--not enough difference in the measured values to be be able to discern the underlying variation. This usually means that the discrimination of the device isn't in line with the (probably) small amount of variation in the data.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#3
FWIW I have had very expensive measurement equipment be useless at measuring things, usually because of the fixturing method, sample prep, or other setting choices.

That said the (easily) informative part of any R&R study is in the details and not the statistical summary. can you post your data?
 
C

Curtis317

#5
Thank you Miner. Can I copy and save the information you have in the link? While I am not sure this is a solution to this issue it may help me with other issues.
 

Miner

Forum Moderator
Staff member
Admin
#6
Yes. I posted all of my blogs publicly and expect all to freely use them as long as they don't claim them as their own.
 
C

Curtis317

#7
This is the data from the GRR. I did two characteristics at the same time since they are part of the measuring program.

Round1Crankshaft GRR 1 12.7 mm10mmRound2Crankshaft GRR 1 12.7 mm10mmRound3Crankshaft GRR 1 12.7 mm10mmCrank no.PersonMeasurementMeasurement Crank no.PersonMeasurementMeasurement Crank no.PersonMeasurementMeasurement10Peggy2.6474.13 5Peggy1.7393.122 2Peggy0.5860.6857Peggy4.1744.003 7Peggy2.2973.202 7Peggy1.993.1535Peggy2.2693.495 8Peggy2.3233.074 9Peggy1.3061.8856Peggy0.3250.862 2Peggy1.5082.041 3Peggy1.372.1821Peggy1.9361.223 6Peggy1.1851.78 4Peggy0.8240.999Peggy4.6026.561 3Peggy2.0322.426 5Peggy0.6950.8892Peggy0.3670.702 1Peggy1.9973.23 1Peggy2.8943.8174Peggy1.3642.131 4Peggy1.4052.336 6Peggy0.9081.4893Peggy0.5860.869 10Peggy2.4394.142 8Peggy0.2460.3398Peggy0.9111.073 9Peggy3.1334.51 10Peggy1.5942.521Round1Crankshaft GRR 1 12.7 mm10mmRound2Crankshaft GRR 1 12.7 mm10mmRound3Crankshaft GRR 1 12.7 mm10mm Crank no.PersonMeasurementMeasurement Crank no.PersonMeasurementMeasurement Crank no.PersonMeasurementMeasurement 3Sandy1.5521.715 3Sandy1.331.532 6Sandy0.8871.145 2Sandy0.9841.285 5Sandy1.271.886 5Sandy2.4713.741 4Sandy0.2750.636 8Sandy0.6221.002 9Sandy1.6422.688 6Sandy4.7086.748 10Sandy3.3784.809 8Sandy0.2390.639 7Sandy2.0683.044 1Sandy0.7370.981 10Sandy1.11.581 5Sandy0.1340.102 6Sandy0.9621.612 7Sandy2.333.34 8Sandy1.5112.231 2Sandy2.2023.59 1Sandy1.5972.065 1Sandy0.7591.089 9Sandy1.7332.493 3Sandy1.732.341 9Sandy1.572.192 7Sandy2.5443.943 2Sandy0.8331.175 10Sandy1.1171.801 4Sandy2.7374.016 4Sandy2.0092.951Round1Crankshaft GRR 1 12.7 mm10mmRound2Crankshaft GRR 1 12.7 mm10mmRound3Crankshaft GRR 1 12.7 mm10mm Crank no.PersonMeasurementMeasurement Crank no.PersonMeasurementMeasurement Crank no.PersonMeasurementMeasurement 8Mike0.9620.987 5Mike0.6651.16 2Mike1.4582.022 3Mike1.8982.448 7Mike0.4160.579 10Mike0.8871.389 2Mike0.991.332 2Mike1.1611.556 7Mike1.2831.77 10Mike1.6542.338 4Mike0.8141.258 6Mike1.7972.428 1Mike0.5711.044 10Mike0.761.151 4Mike1.2421.822 9Mike1.7252.468 8Mike0.3260.728 9Mike1.1511.659 6Mike1.72.504 9Mike1.1811.1752 3Mike1.6692.293 7Mike1.6652.501 3Mike0.0860.325 5Mike0.7361.145 5Mike0.3310.442 6Mike0.8771.12 8Mike0.4710.507 4Mike1.9462.744 1Mike0.5321.004 1Mike2.1472.998
 
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