Gage R&R with CMM 1X1X10

[Mary - QA Manager]

My new assignment is to run a gage R&R on one part with one operator ten times (1X1x10) on CMM.
I found an excel sheet from this site not sure what all the figures mean.

That's for your help!

Mary

 

[Englishman Abroad]

Mary,

If you do not understand the sheet, I suggest you look at Miner's blog on MSA.

Look in blogs on the Menu bar at the top of the page and search for Miner.

 

[Johnson]

Dear Mary,

In fact, the calculation in the Excell sheet is not Gage R&R. It is another capability index of measuring equipment Cg=(Upper tolerance-Lower tolerance)/(5.15 *standard deviation). Cgk is another index. Here 5.15 can be defined differently based on the measuring equipment requirements. Both Cgk and Cg measure 1 part (or master sample) by one operator for a certain times, for example 10 times at your example.
For Gage R&R , it normally need 10 parts, 3 operators, each operators measuer 10 times.

I would suggest you should read AIAG's MSA manual, or VDA 5.

Johnson

 

[Mary - QA Manager]

Thanks for your reply. I went back to the customers requirements just to make sure I understand what it is they are looking for.
"CMM gage studies must be carried out on 1 part, inspected 10 times by I worker or inspector using the following calculation formula:
% of repetability=100%(maximum range/tolerance band)
I am not that well versed with excel to create such a sheet. I have asked my customer for a sheet but they do not have one.
Thanks!
Mary

 

[Johnson]

For example, the part tolerance is 10+/-0.5 mm, then the tolerance band =10.5-9.5=1.0
If the 10 measurements are:
9.6 9.8 10 10.2 10.4 9.6 10.1 10.2 9.7 10.2,
the the maximum range is (max -min)= 10.2-9.6=0.6
% of repetability=100%(maximum range/tolerance band)=100%(0.6/1.0)=60%.

Then questions again:
1) What the requirements of the measuring equipment capability, is <10%, or <50%, <80%?
2) The customer must tell if the above interpretion is correct or not.

 

[Johnson]

I tried the Excel sheet you attached.
The principle is correct, but the criteria is very high ! You should consider if it is suitable for your company.
I attached the example for your reference.

 

[Mary - QA Manager]

Please take a look at the newest spreadsheet...
Thanks
Mary

 

[Johnson]

Looks good ! If the customer agree with it, you can use it. I mentioned customer for several times, because you see the calculation and the factor could be different. Here the 6 is a factor, but some customer may chosen to use 4, or 5.15>

Part % R = (Standard Deviation x 6 / Part Tol. Range) x 100

 

[JAltmann]

Please take a look at the newest spreadsheet...
Thanks
Mary

That is the typical formula/study sometimes referred to as a P/T Ratio. The 6 sigma follows the change with MSA 3rd (or 4th?) edition. This is a good test not just for CMM's but also for reference before performing a full GR&R as if you can't pass this test then the GR&R will be worse and the time wasted.

Most strive for a value outcome of under 10% for this test to be considered passing, but this should be discussed internally and with your customer (SQE typically).