Clarification of the Impact of Out of Specification Parts on %P/T

[Mohit Malkani]

Can someone clarify the impact of out of spec parts on %P/T?? (Total tolerance 0.008", parts oversized by 0.002")

Thanks

Mohit

[Chance]

Can someone help on this one? Thanks.

[Jim Wynne]

In Reply to Parent Post by Mohit Malkani

Can someone clarify the impact of out of spec parts on %P/T?? (Total tolerance 0.008", parts oversized by 0.002")

Thanks

Mohit

If you're referring to percentage of tolerance, it would seem that you're using 125% of it. Why are you using out-of-tolerance parts in a gage study? If you're not concerned about the out-of-tolerance condition, you should look at percent of variation, which doesn't concern itself with tolerance.

[Mohit Malkani]

Not using out of spec (oos) parts intentionally. Found out the hard way that parts are bad.

Thanks

Mohit

[Miner]

If there is not a linearity issue with your gauge, the part dimension will have no impact on the R&R as a % of Tolerance (i.e., P/T Ratio). However, a serious linearity issue could have an effect on it.

[Deep Krothapalli]

Miner - Can you please clarify this if I am missing something here?

Since variances are additive,

Total Variance = Variance between Parts + Variance between Operators + Variance from Operator - Part interaction + Variance from Gage repeatability


%P/T = Variance of Measurement System/Tolerance
= (Total Variance - Variance between Parts)/Tolerance

Using out of specification parts is likely to increase variance between parts. If the operator interaction with the gage is not changed with the out of specification parts, then it most likely that %P/T is decreased with the use of out of specification parts.