Acceptable % on a Gage R

Danny Hoover

Involved In Discussions
#1
Good morning,
I have just started at a new company and one of my duties is to help get a SPC program in place. I have started running gage R studies(1x10) on all newpieces before we do a full r&r/cap study/layout. I have looked around for an answer, but here they accept a R study if it is <30%, which causes the r&r to typically fail. I have a new part that the r study is 19% on one dimension, when I copy and fill out the r&r with the R data it shows 29%. What is the standard accepted R% to pass and move on?
Thanks,
DH
 
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Jim Wynne

Staff member
Admin
#2
Re: Acceptable % on a Gage R&R

Good morning,
I have just started at a new company and one of my duties is to help get a SPC program in place. I have started running gage R studies(1x10) on all newpieces before we do a full r&r/cap study/layout. I have looked around for an answer, but here they accept a R study if it is <30%, which causes the r&r to typically fail. I have a new part that the r study is 19% on one dimension, when I copy and fill out the r&r with the R data it shows 29%. What is the standard accepted R% to pass and move on?
Thanks,
DH
Welcome to the Cove. :bigwave:

I'm not sure what the point is of doing an "R" as a prelim to R&R, nor have I ever worked anywhere where such a thing was done. The numbers and pass/fail criteria in traditional GR&R studies are tainted by a fair amount of voodoo math and shouldn't be considered the only criterion in evaluating a measurement system. You should be looking at the numbers in order to find out what they're telling you regardless of the R&R percent results.

In the absence of specific customer requirements, whether or not a measurement system is considered acceptable should not be determined by the R&R percentages alone. You need to consider the application and its attendant risks in making decisions.
 

Danny Hoover

Involved In Discussions
#3
Thanks Jim,
We measure by hand thin plastic parts and we need to get the measurements to repeat. The R study shows if the part could be measured by one person and repeat. The time saver is if it fails an R study, we do not run a full r&r/capability/layout study, but we ask the engineer and customer for input on tolerance relief, gaging needed, etc. These are automotive parts with customer required spc points if that helps.
Thanks,
DH
 

Ninja

Looking for Reality
Staff member
Super Moderator
#4
Re: Acceptable % on a Gage R&R

I'll typically do an "R" study myself as well with new equipment, but not as a formal thing, and not for determining acceptance...just for a reality check before I invest the labor to do the full GRR.

As Jim notes, the % result isn't very valuable from this 'reality check' kind of study...but the reality check part is. If I measure 5 parts twice each (2x5) and my EV% is 30% of my tolerance, I need to look at how I'm using the tool before I get two other people involved. If the Equipment variation is even approaching 10% of tolerance for me, why would I think it would be better for anyone else (or more to the point everybody else).

There's a value to a quick test in that I can revise the test protocol before using the labor to do the 'official' test...but I don't see a value in defining acceptance criteria for the quick test. Look at your results and see if the current test method has a chance at being acceptable though full testing.
 

Danny Hoover

Involved In Discussions
#5
Thanks Ninja,
You use the test exactly as I am thinking. I was just wondering if a common
"stop" % existed. I typically get the r&r to come in around 2x the R alone.
I am required to conserve as much inspection time as possible, and I hate having to run the studies over after addition people are involved.
:agree:
DH
 

Jim Wynne

Staff member
Admin
#6
Thanks Ninja,
You use the test exactly as I am thinking. I was just wondering if a common
"stop" % existed. I typically get the r&r to come in around 2x the R alone.
I am required to conserve as much inspection time as possible, and I hate having to run the studies over after addition people are involved.
:agree:
DH
I'm sure there's no such number. I can see doing a little informal trial when there's a novel situation--something unusual in the parts or the device, or both, but for everyday purposes I think that people should be generally aware of the parts and the devices and the competency of operators to the extent that such a thing shouldn't be necessary.
 
J

JAltmann

#7
Re: Acceptable % on a Gage R&R

If i had to give a number 10% comes to mind. But when i do the gage R study i am looking for the sources of error. Is that error attributed to the operator? The gage, combination?

If it is all in one area i would try to correct the issue before proceeding to a full GR&R.
 

Danny Hoover

Involved In Discussions
#8
Re: Acceptable % on a Gage R&R

Thanks James,
I am looking to save time without having to do a complete study. The flimsy nature of some parts often make it impossible for the lab to get the parts to repeat. After they pass in the lab, we have the criteria and method for floor inspectors to do the checks, whether gages,non-contact, or hand tools are used. We can tweak the process if the floor has any trouble doing the inspections.
Thanks,
DH
 
I

ivijaya

#9
Re: Acceptable % on a Gage R&R

A P/T ratio less than 0.1 indicates that the measurement system can reliably determine whether any given part meets the tolerance specification. A P/T ratio greater than 0.3 suggests that unacceptable parts will be measured as acceptable (or vice-versa) by the measurement system, making the system inappropriate for the process for which it is being used
 
S

sitapaty

#10
Re: Acceptable % on a Gage R&R

I want a clarification from you.Are you calculating R&R as % of DRG. TOLERANCE or % of PROCESS VARIATION observed in your trial.?
Theoritically if the R&R value is <10% of process variation the gauge is acceptable.But for practical purposes if R&R is <10% of drg.tolerance it is ideal.In special cases <30% is accepted.
-SITAPATY
 
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