GR&R (Gage R&R) Anova spreadsheet is telling us that a gage is not working

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Comet77

#1
I need some help. We have filled in all the information form a GR&R in the GR&R anova spreadsheet and it is telling us that the gage is not working even though everything is well within spec. Help please.
 

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B

bmccabe - 2006

#2
Minitab produced this ANOVA from your data. I hope it helps.

Study*Var %Study*Var
Source StdDev (SD) (6***SD) (%SV)
Total Gage R&R 0.0001107 0.0006640 42.10
Repeatability 0.0001035 0.0006208 39.36
Reproducibility 0.0000393 0.0002357 14.95
Monkey 0.0000393 0.0002357 14.95
Part-To-Part 0.0002384 0.0014304 90.70
Total Variation 0.0002628 0.0015770 100.00
 

Miner

Forum Moderator
Staff member
Admin
#3
Comet77 said:
I need some help. We have filled in all the information form a GR&R in the GR&R anova spreadsheet and it is telling us that the gage is not working even though everything is well within spec. Help please.
The answer will depend on what you are using the gage to do.

If you are using the gage to inspect parts to specification, the gage is acceptable because the P/T Ratio is 12.5% of Tolerance.

If you are using the gage for SPC, the gage is not acceptable because the %GRR is 39.5% of process variation with an ndc (number of distinct categories) = 3. This means the gage can only distinguish low, medium and high values within the process variation.

The discrimination and reproducibility of the gage is good, the problem lies with the repeatability. One area that I recommend investigating further is the within part variation or variation in form. I noticed in the Measure By Part graph that there are significant differences in the repeated measures variation from part to part (see parts # 1 & 8 versus parts #3 & 4). If parts # 3 & 4 have significant variation in form (e.g. roundness) compared to parts 1 & 8, you would see a graph similar to this.
 
C

Comet77

#5
Howard Atkins said:
Or I am loosing my mind or there is something wrong with the formulas but I cannot see any results in the excel
You noticed that as well? :agree1:
Well we ran the same numbers in a seperate (seperate from standard) spreadsheet and everything seems to come out fine in that one. In order to use this one we are having someone looking into it today. Perhaps the owner might consider purchasing updated software. :lmao:

Thanks for the assistance everyone.
 
T

Timmot

#6
:bigwave: Same here, I entered the values used in the MSA manual and the results look good but are zero when I enter my own values it can be somthing to do with negative numbers defaulting to 0 ?

I have never used Anova but see its use as an analys tool when the GGR fails, so I have been trying to do my own Anova spreadsheet but don't fully understand the formulers in the MSA manual, so I, and I'm sure others would be happy if some maths whizz checked the excel spreadsheet in this thread or shares one that has already been checked !
 
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C

chalapathi

#7
Selecting Sample for R&R Study

Comet77 said:
I need some help. We have filled in all the information form a GR&R in the GR&R anova spreadsheet and it is telling us that the gage is not working even though everything is well within spec. Help please.
In your data, the specification is 0.57 - 0.062 and the 10 parts you have selected are representing this range. Typically, the entire range and beyond needs to be covered. My guideline for selecting parts is like this "6 parts with in the specification range and 2 parts each above USL and below LSL". In your case this guideline is not followed.

In the ANOVA method, I checked with my template and it is showing that the interaction is not significant in your case and you can use average and range method. The zeros in ANOVA table are comming because you need to display upto 7/8 significant digits. In your case Discrimination is 0.0001

Looks like there are some errors in your template (in ANOVA temple) check the caculations.
 

Miner

Forum Moderator
Staff member
Admin
#8
chalapathi said:
In your data, the specification is 0.57 - 0.062 and the 10 parts you have selected are representing this range. Typically, the entire range and beyond needs to be covered. My guideline for selecting parts is like this "6 parts with in the specification range and 2 parts each above USL and below LSL". In your case this guideline is not followed.
I disagree with this guideline unless you only intend to evaluate the P/T ratio for the suitability of the gage to inspect product to tolerance.

If the gage is intended for process control, the spread of sample parts should have a standard deviation similar to the short-term standard deviation of the procress the parts came from. This is the only way to accurately evaluate the GRR as a percent of the process variation, and its suitability for process control.
 
C

chalapathi

#9
Miner said:
I disagree with this guideline unless you only intend to evaluate the P/T ratio for the suitability of the gage to inspect product to tolerance.

If the gage is intended for process control, the spread of sample parts should have a standard deviation similar to the short-term standard deviation of the procress the parts came from. This is the only way to accurately evaluate the GRR as a percent of the process variation, and its suitability for process control.
Your point is valid. However, taking parts spread over the entire tolarance range and beyond is important, as we are trying to look at the capability of the Measurement System and not the capability of the process. The process is operating with in the range today and will shift in case of special causes, at that time how this measurement system is going to do its job? The repeatability and reproducibility errors may be within acceptable limits within the process limits and the errors may be abnormal out side the range. Do you think, it is not reasonalbe to address this aspect?
In my experience, I had seen that one measurement was able to recognize the good part consistantly and not recognizing the rejected part correctly every time. Some time readings are within the limits and some times out of specification limits.
 

Jim Wynne

Staff member
Admin
#10
chalapathi said:
Your point is valid. However, taking parts spread over the entire tolarance range and beyond is important, as we are trying to look at the capability of the Measurement System and not the capability of the process. The process is operating with in the range today and will shift in case of special causes, at that time how this measurement system is going to do its job? The repeatability and reproducibility errors may be within acceptable limits within the process limits and the errors may be abnormal out side the range. Do you think, it is not reasonalbe to address this aspect?
In my experience, I had seen that one measurement was able to recognize the good part consistantly and not recognizing the rejected part correctly every time. Some time readings are within the limits and some times out of specification limits.
The sample parts should reflect the operating range of the process. If that range includes parts outside the specification limits then in a sense, the measurement system has done its job and now you have a process control problem.
 
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