Gage R&R - Calculating by Specification Tolerance vs. Study Variation - Differences

Y

Yew Jin

#1
Hi all,

What is the difference when we calculating the GR&R which based on the spec tolerance and % study variation. In minitab, we will use 6sigma to calculate the total % of study variation but I don't know how to perform the GR&R by spec tolerance in minitab. Can somebody help?:rolleyes:

Second, when we have the one sider spec, can we calculate the GR&R based on the spec tolerance?:confused:

Thanks and regards
YJ
 
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Miner

Forum Moderator
Staff member
Admin
#2
Re: Difference between GR&R calculating by spec tolerance and study variation

You perform the study the same way as any other, but when performing the analysis, select the Options button and enter the tolerance. Minitab will then perform the additional calculations and add then to the Session window.

Minitab also allows entry of one-sided specifications.
 
Y

Yew Jin

#3
Re: Difference between GR&R calculating by spec tolerance and study variation

Thanks Miner;) :applause:

But is there any specific difference when we use spec tolerance or study variation (6 sigma) to calculate the GR&R? i found the same question when I took the CQE course in last month. :truce:
 

Miner

Forum Moderator
Staff member
Admin
#4
Yes, there is a difference.

%GRR specifically means GRR as a percent of the study variation. This is used to determine the suitability of a gage for use in process control or for use in continual improvement studies such as hypothesis testing, DOE's, etc.

When GRR is compared to the tolerance, it is called the P/T Ratio, not %GRR. This is used to determine the suitability of a gage for product acceptance to the specification.
 
Y

Yew Jin

#6
Hi All,

I have any issue on the P/T ratio and GR&R by %study variation calculation.
After analysis the data, the P/T ratio = 31.53% and the GR&R =9.01%.
Can I accept gage?:confused:
 

Miner

Forum Moderator
Staff member
Admin
#7
Hi All,

I have any issue on the P/T ratio and GR&R by %study variation calculation.
After analysis the data, the P/T ratio = 31.53% and the GR&R =9.01%.
Can I accept gage?:confused:
It depends on what you use the gage for. The %GRR of 9.01% means the gage is acceptable for process control, but the P/T Ratio of 31.53% means that the gage is not acceptable for use as an inspection gage.

Of greater concern is that this may mean one of two things:
1. Your process is not capable of meeting the tolerance. The only way you can achieve these results is for your process variation to be greater than your tolerance.

2. Your sample variation does not match your actual process variation. If this is the case, your %GRR is not valid (P/T Ratio IS valid), and you need to repeat the study using samples that reflect the actual process variation.
 
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