Minitab version 15 Gage R&R and Single Sided Specification

K

Kalpol92

OK so i have a question.

the new version of minitab allows you to input the specification limits for GR&R studies so you can calculate the PT ration(GR&R tolerance) no problems here.

However if you have a single sided spec i have always been taught that you cannot calculate a PT Ratio. But Version 15 of minitab spits out a PT ratio if you put in a single sided spec.

Can anyone explain why this is and how minitab is calculating it?????

Kalpol
 
K

Kalpol92

Re: Minitab version 15 Gage R&R and single sided spec.

any ideas anyone?
 
K

Kalpol92

Re: Minitab version 15 Gage R&R and single sided spec.

Oh come on someone must have an idea?????
 

harry

Trusted Information Resource
Re: Minitab version 15 Gage R&R and single sided spec.

Oh come on someone must have an idea?????

I am sorry but you'll have to be patient a bit because there are not really that many users that participate in this area. Apart from Allattar, we have reynald, Miner and another few that I can't recall off-hand.
 

Miner

Forum Moderator
Leader
Admin
Many of us cannot access the Cove forums while at work, so this adds a delay to responses.

I investigated Minitab's formula for calculating % Tol for a one sided tolerance. It is essentially the same concept as the Cp/Cpk calculation.

% Tol for a double sided tolerance is (6 * StdDev measurement) / (USL - LSL)

% Tol for a one sided tolerance is (3 * StdDev measurement) / (USL - Mean) or (3 * StdDev measurement) / (Mean - LSL)

I have mixed feelings about this approach. If you normally have distance between the mean and the SL, your P/T Ratio should look good. The problem arises when you must inspect product near the SL. I personally would use a Gauge Performance Curve to assess the gage suitability.

See the file in my blog, MSA Part 3, for such a curve.
 
A

Allattar

Sorry for being away so long :)

Miner beat me to it as normal.

Perhaps the probabilities of misclassification could be useful here on a one sided tolerance as well?
 
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