Is ANOVA Gage R&R the best method? Reproducibility issues (no inspector effect)?

R

Rob Nix

#1
I need help! (yeah, yeah, I've needed it for a long time; right :vfunny: )

Anyway, a potential new customer has provided us with their specifications during contract review, and as part of their acceptance plan are requiring the following:

An ANOVA style Gage R&R (re: AIAG MSA) must be conducted on 20 parts, 5 repetitions each (randomized). There doesn't appear to be any reproducibility issues (no inspector effect). I am just wondering if this is the best approach or if another method would work better. Any thoughts from the panel of experts??? :confused:

NOTE: They also require we use Minitab (which we do not have) but allow for us to submit/recommend a different software and/or method.
 
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A

Al Dyer

#2
If the customer is looking for an ANOVA R&R with the use of specific software I would tend to believe one of 3 things:


1: The gage man has stock in Minitab,

2: The gage people are not sure what they are looking for,

3: Their customer has the same requirement.

Surely not an expert on ANOVA myself, I would invite Atul to take a look at your situation.

Al...:biglaugh:
 
A

Atul Khandekar

#3
Apart from the 3 Al mentioned, I can't think of any reason for mandating 20 parts in an R&R study. ( More the merrier?). Also I would like to know the rationale for 5 repetitions. One reason could be reduce the margin of error by averaging more values. But this would probably mean that the measurement process is too complex and that repeatability may be in doubt. Why not do a standard 10x3x3 ANOVA? ANOVA is prefered over Range-Average because it would bring out interactions, if any. This may also provide evidence that reproducibility is not an issue.

Also, as Rob has said, if the reproducibility is really not an issue, I think a simple P/T ratio or the Raffaldi method (that has been discussed here before) should be sufficient. (You can download the GRR freeware from my website for this.)
 
R

Rob Nix

#4
Atul,

Thanks for the validation of my thoughts on this. :agree: Earlier today, I sent the proposals engineer a paragraph to add to the proposal that suggests using a standard 10X3 or P/T ratio, to be reported on using MS Excel (not Minitab). I might also add, your software.

p.s. Thanks for the freeware. :bigwave:
 
S

sbickley

#5
Can you direct me to the freeware referenced in this thread? This would benefit me as well.

Thx
 
G

Graeme

#6
sbickley said:
Can you direct me to the freeware referenced in this thread? This would benefit me as well.

Thx
If you click on Atul's name in his post you will open his public profile. The web site link is in there.

GCP
 

Govind

Super Moderator
Staff member
Super Moderator
#7
If I may add to Atul's reply;
I prefer ANOVA method for its ability to determine the effects and its significance.

Here is an example of MiniTab ANOVA method Gauge R & R results:
Two-Way ANOVA Table With Interaction
Source DF SS MS F P
Part 9 2.05871 0.228745 39.7178 0.000

Operator 2 0.04800 0.024000 4.1672 0.033

Part *
Operator 18 0.10367 0.005759 4.4588 0.000

Repeatability 30 0.03875 0.001292

Total 59 2.24913

F- Determines if the effects of Operator, Part, or Operator*Part significantly impact the measurement.
P-value associated with F. P Part, for example, is the probability of seeing an F statistic as large or larger than the calculated one, assuming that all parts share the same mean. So as F gets larger, P gets smaller. A small P implies that the assumption of all parts sharing the same mean is probably not true.

This information is valuable for decision making.
Regards,
Govind.
Note: Forum experts, please suggest ideas to align the table value? Looks ok during editing, but misaligned after posting :mg:
 
Last edited:
S

sbickley

#8
Govind,

Can you also provide a legend for your other headings such as DF, SS and MS?

Thanks,
Scott
 
C

cyding

#10
G R&R

Hi, I have just registered to this web page few weeks ago. I find it very useful.

At this moment, I do not how to raise a new thread. Anyway, the topic is still G R&R.

I am wondering, how should we choose the samples for G R&R study. Can we pick randomly from the production or specially made some samples that fall within and slightly out of specification samples for G R&R study?

From my experience, the randomly pick samples will tend to have high G R&R value. Therefore, we tend to choose samples that will have wide range (for example : lower side of the spec, middle of the spec & higher side of the spec). Generally, we want to create high part-to-part variation to get better G R&R value.

Is it wrong, we conduct G R&R in this manner?

Thank you.
 
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