# How do I do a GR&R study if there is no specified tolerance?

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#### kristin

How do I do a GR&R study if there is no specified tolerance?

I am writing a proposal for a supplier to include GR&R and Cpk data with shipments. One very important specification for this material invloves only a lower limit (example, >50 MPa). All of the formulas I have seen for EV and AV involve using the specified tolerance. Since I don't have a tolerance specified for this parameter, is it possible to calculate the %R&R?? Is it possible to do a GR&R study without changing this spec?

I would appreciate any suggestions. I will be performing a process capability analysis (Cpk) for this particular parameter and I know this is possible when only one limit is specified.

Thanks!!

A

#### Al Dyer

Kristin,

I'm not sure about formulas for your situation, but I pose this:

As the customer, could you set an upper limit for your supplier?

i.e. >50 ----- < 300

I guess I would have to ask why there is no upper limit? I don't know your process.

Only you or your company has the knowledge to know what that upper limit would be.

ASD...

A

#### aysan

Hi
there are three types to calculate EV%, AV% and R&R%:

EV%=EV/RF
AV%=AV/RF
R&R%=R&R/RF

where, Reference Figure is one of these parameters:
- Tolerence(USL_LSL)
- Process Variation (6 sigma)
- Total Variation(TV=PV+R&R)

If you don't have Tolerence, you can use two types else to calculate those parameters.

Aysan

D

#### Dave Stauffer

Contact AIAG and request an MSA Manual.
Look for the forms that utilize process variation rather than tolerance for finding the percentage R&R. ANOVA does this.

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Dave Stauffer

A

Good call!