2 Gage study MINITAB question
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 This topic has 7 replies, 8 voices, and was last updated 14 years ago by Michael Mead.

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January 24, 2005 at 9:17 pm #38177
I am comparing two gages. I have 1 operator and 10 parts. Each part was measured twice with each gage. How can I compare the data? Previously I ran another study with only 1 gage, 2 operators and 10 parts. Each part was measured twice by each operator. I don’t believe it is correct to run that Gage R&R study (crossed) again for this data.Do you have any suggestions on what to do? I would like to compare the two gages and show that one is more accurate and repeatable than the other.Thank you in advance for any help you can offer,~RUTH~Ruth D. AyalonMoog(716) 687 – [email protected]
0January 26, 2005 at 6:22 pm #114028Hi Ruth!
I noticed that you haven’t gotten a reply yet so will give it my 2 cents….
The GR&R will give you a measure of how much variation is associated with the measurement process… This is related to the gage precision…. To do this properly you need to run the classic GR&R using one measurement system (gage) and at least 2 people. Since you have already completed one gage GR&R you should run the same evaluation on the second gage to be able to accurately contrast their performance….
The second area is that of accuracy… A GR&R will not help you here… To accurately assess accuracy you need to look at how the measurement system (gage) performs against a known standard. Most cal labs (inhouse or outhouse) should be able to verify the accuracy of the gage(s) in question….
Since you are planning to contrast the accuracy and precision of both gages you also will want to use similar evaluation processes (people, samples etc) for both.
Hope this helps…..
Best Regards,
Bob J0January 31, 2005 at 7:25 am #114205
Vivek ShrivastavaMember@VivekShrivastava Include @VivekShrivastava in your post and this person will
be notified via email.Hi,
Lets understand first what we are trying to do in GRR.
we are trying to see what ratio of observed variation is being contributed by measurement system. And we want SS (measurement system) to be less than 30% of SST.
Now if we can calculate SS (measurement) and SST our problem is solved.
What I’ll suggest is measure your 10 parts by multiple operators, each part being measured by every operator multiple times. and every part to be measured by every operator on both the gages.
Then do ANOVA wrt. part number. minitab reprt will give you SS part, SST and SS error. Divide SS error by SST and this is the contribution due to measurement system variation.
Regards,
Vivek
0January 31, 2005 at 1:58 pm #114220Since the gage is the main piece of the puzzle, be sure to use the same operators and parts when completing both GR&R. May sound trivial, but this will eliminate any question about the validity of this test. I agree with the GR&R analysis and even ANOVA from the previous posts, but don’t forget about control charts. A simple Xbar and R chart for each gage sure will tell you a lot and helps quantify your gage expectations when running later experiments.
0February 1, 2005 at 3:34 am #114274
AJIT SHARMAParticipant@AJITSHARMA Include @AJITSHARMA in your post and this person will
be notified via email.Mr. bob j is absolutely right.
you need minimum 2 people for gage r&r
then you may comapre the results of both the gages in terms of
1) %contribution
2)%study variation
3) distinct catagories.
And then decide which measurement system is best.
Accuracy has nothing to do with G R&R.
We have calibration for that.
AJIT SHARMA0August 7, 2008 at 6:22 am #174644
Thilanka MarasingheMember@ThilankaMarasinghe Include @ThilankaMarasinghe in your post and this person will
be notified via email.Pls advice me how to get Gage R&R study results after entering the data
0August 7, 2008 at 7:56 am #174645Hai Ruth,
You can compare it in a lot of ways. Before you choose one: choose what you want to decide upon.
Here my view (summarized)AbsoluteEvaluation: If you want to prove that each gage has a good Gage r&R value you just have to do the other one also (no shortcuts)
RelativeComparison: Just fill in gage1 and gage2 in the operator column and perform your gage r&R. The reproducibility value you get is an indication how much different the 2 gage’s are FOR THAT ONE OPERATOR ONLY!. Mathematically not nice, but practical. Alternative: Regression between the 2 gage’s (scatterplot) or paired ttest for bias only.So yes since ‘all’ data concerns 1 operator you can only draw the conclusion on 1 operator.
And I hope that the 2 operators are representative for all operators you get data from (because that’s your assumption for the conclusion). Note: Mathematically 2 operators is not enough. It should be >=30. But since that is totally unrealistic the ‘standard’ that everybody (should) use is 3 operators.
hope this helps.0August 7, 2008 at 9:06 am #174651
Michael MeadParticipant@MichaelMead Include @MichaelMead in your post and this person will
be notified via email.Hello Ruth, it seems noone is answering your question directly. Here is a procedure that will work:
Calculate the range for each of your 20 pairs of measurements.
Find tthe average range for each gage. (R1 and R2) Call R1 the larger range.
Find F’ = R1/R2.
If this ratio is greater than 1.9 then the gages have different amounts of variation with 95% probability.
For the guys who always check what I write: Use Juran’s Quality Control Handbook, 4th edition, Appendix II, Table M.
Good luck.
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