P
pinpin - 2009
Sir,
If the part dimension is designate as a Critical one that require SPC control, then this CMM shall meet 10% GRR or Total Variation, right?
Sir,
If the part dimension is designate as a Critical one that require SPC control, then this CMM shall meet 10% GRR or Total Variation, right?
That is correct per the AIAG MSA manual.
However, remember that unless your customer dictates compliance to this manual, you are still free to make your own rules. I noticed that you had reviewed the threads with Donald Wheeler's articles, so you know that SPC can still detect process changes at %GRR much greater than 10%. If your choice is not dictated to you, use what works for you.
However, remember that unless your customer dictates compliance to this manual, you are still free to make your own rules. I noticed that you had reviewed the threads with Donald Wheeler's articles, so you know that SPC can still detect process changes at %GRR much greater than 10%. If your choice is not dictated to you, use what works for you.
R
rick tompkins - 2013
Using this software (basic Gage Tracker), I toolk the option of using the format of the "long-GM" view instead of the 'long-AIAG' view. All the bottom row of percentages were removed and only the field headers were left, empty.
Then, I tabbed the "long-AIAG" box to show it on the printer, and I submitted the Study with the 6.4%.
I thought of circling the %Tol with the full set of data but did not want to answer questions on the 16%TV.
In today's MSA activities, is the %Tol not favored anymore for Gage R&R?
I wonder how I would present a less than 10% Total variation on a Study with close tolerance and very small variation on a random sample of parts.
Funny, but the same data in an ANOVA study showed no formula results and my only recourse was to print a chart of part-to-part variation by appraiser.
Guess I need an upgrade to this software, huh?
Rick, Illinois
Then, I tabbed the "long-AIAG" box to show it on the printer, and I submitted the Study with the 6.4%.
I thought of circling the %Tol with the full set of data but did not want to answer questions on the 16%TV.
In today's MSA activities, is the %Tol not favored anymore for Gage R&R?
I wonder how I would present a less than 10% Total variation on a Study with close tolerance and very small variation on a random sample of parts.
Funny, but the same data in an ANOVA study showed no formula results and my only recourse was to print a chart of part-to-part variation by appraiser.
Guess I need an upgrade to this software, huh?
Rick, Illinois
Many customers do not understand MSA beyond the jargon and 10%.
P/T Ratio (%Tol) is valid, but you need to make a rational argument that the CMM is not used for SPC, but for inspection. Then support your choice of metric, by showing that P/T Ratio is intended for this purpose.
P/T Ratio (%Tol) is valid, but you need to make a rational argument that the CMM is not used for SPC, but for inspection. Then support your choice of metric, by showing that P/T Ratio is intended for this purpose.
Re: A little clarification on 10:1
Preface: In my quest towards the 17025 guideline, I am daily learning/advancing my knowledge. So reading through old posts helps me immensely.
I have a question on T.U.R. I understand the Test Accuracy Ratio. The accuracy of the standard should be at least four times greater than the accuracy of the U.U.T.( Unit Under Test).
I understand uncertainty calculation of the standard being used (should be less than 150 microinches). The above example presents 600 microinches as the expanded uncertainty for the U.U.T. 1) How (or are you expected to) calculate an uncertainty for the U.U.T.? It seems to me you are just assessing against a tolerance of 600 microinches.
2) If I am currently maintaining 4 to 1 test accuracy ratios, doesn't that by default, imply that I have less than 4 to 1 test uncertainty ratios?
Preface: In my quest towards the 17025 guideline, I am daily learning/advancing my knowledge. So reading through old posts helps me immensely.
I have a question on T.U.R. I understand the Test Accuracy Ratio. The accuracy of the standard should be at least four times greater than the accuracy of the U.U.T.( Unit Under Test).
I understand uncertainty calculation of the standard being used (should be less than 150 microinches). The above example presents 600 microinches as the expanded uncertainty for the U.U.T. 1) How (or are you expected to) calculate an uncertainty for the U.U.T.? It seems to me you are just assessing against a tolerance of 600 microinches.
2) If I am currently maintaining 4 to 1 test accuracy ratios, doesn't that by default, imply that I have less than 4 to 1 test uncertainty ratios?
R
rick tompkins - 2013
The parts in the Study checked to .0005" tolerance, with my CMM Z axis locked for a specific point of measurement; this is just to report to you that the conditions were tightly controlled...
Again, the CMM is used for inspection and I have no plans for its SPC use (Ppk and Cpk studies, yes, but no longe-range inprocess actvity, thank you).
If the P/T is 6.4% and the Total Variation is ~16%, I'll present my customer with the "abridged" report showing only the P/T.
The customer is a medical device company and may not want the P/T%.
I'll know soon enough, but if less than 10% is their requirement on Total Variation, another part with a larger tolerance (let's say +/- 0.01 mm) and less variation should make them happy. Perhaps an added .0003" will assist in this case.
Honestly I think the 10% guideline on TV is excessive, especially with three factors involved (equipment, appraiser, and part tolerance). I had been satisfied with this, the P/T, for too many years to share here. Of course, part tolerance has always been key for the gage selection, but it's always brought a Gage R&R % into acceptability.
Any thoughts?
Why isn't the Tolerance factor detailed in the current MSA from AIAG?
Rick, Illinois
Again, the CMM is used for inspection and I have no plans for its SPC use (Ppk and Cpk studies, yes, but no longe-range inprocess actvity, thank you).
If the P/T is 6.4% and the Total Variation is ~16%, I'll present my customer with the "abridged" report showing only the P/T.
The customer is a medical device company and may not want the P/T%.
I'll know soon enough, but if less than 10% is their requirement on Total Variation, another part with a larger tolerance (let's say +/- 0.01 mm) and less variation should make them happy. Perhaps an added .0003" will assist in this case.
Honestly I think the 10% guideline on TV is excessive, especially with three factors involved (equipment, appraiser, and part tolerance). I had been satisfied with this, the P/T, for too many years to share here. Of course, part tolerance has always been key for the gage selection, but it's always brought a Gage R&R % into acceptability.
Any thoughts?
Why isn't the Tolerance factor detailed in the current MSA from AIAG?
Rick, Illinois
C
Coleman Donnelly
Is the 10-1rule documented anywhere by AIAG?
Coleman,
If you have the AIAG MSA Manual, look at:
- Page 5 underneath "Basic equipment."
- Page 39 see paragraph 1)
Stijloor.
C
Coleman Donnelly
I guess I should be a little more specific....
We use a universal gage to measure the length of our parts. The universal tollerance for the length of a part is +/- .040". That means that the tollerance of the length gage should be +/- .004". We set our length gages using a transfer standard. My understanding is that the length of the transfer standard should be +/- .0004". Maybe i am wrong - if so please enlighten me! - However if i am not wrong - how do i prove my argument? Preferebly using AIAG manuals!
We use a universal gage to measure the length of our parts. The universal tollerance for the length of a part is +/- .040". That means that the tollerance of the length gage should be +/- .004". We set our length gages using a transfer standard. My understanding is that the length of the transfer standard should be +/- .0004". Maybe i am wrong - if so please enlighten me! - However if i am not wrong - how do i prove my argument? Preferebly using AIAG manuals!
