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cgk, process capability
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  #1  
Old 19th March 2000, 04:52 AM
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Question What is Cgk? (Index of Testing Means Capability)

Can anyone point to any references about what exactly is Cgk (Index of Testing Means Capability) and how is it calculated?

I found only one reference to it on the web at http://www.csigmbh.de (Sorry, I don't remember the complete URL of the page right now)

Thanx in advance.

Atul Khandekar


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Old 20th March 2000, 11:01 AM
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Atul,
In a previous employment we used to calculate Cg which was done by comparing six standard deviations (from the measurement system) to one tenth of the process specification limits.
(tolerance/10)/(6*SD of measurement system).
I guess if you used a traceable master to do your study, you could then apply +/- one fifth of the spec to produce an upper and lower limit. Then calculate Cgk upper & lower using 3 SD's as in Cpk calcs.
-for instance Cgk upper = "Upper Limit"-trial mean/ (3* trial SD)

Seems like a lot of effort to produce a capability index that no-one recognises though!
Cheers

Brian
I think the old (outdated) Ford R&R manual had details on this.
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Old 29th March 2000, 08:30 AM
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Yin Yang

From: Tomo Doran
Newsgroups: misc.industry.quality
Subject: Re: What is Cgk?
Date: 29 Mar 2000 03:51:31 GMT

The capability indices Cg & Cgk are related to gaging and compare the variation and location to a reference figure - often 10% of process tolerance in the same way that Cp & Cpk is derived.

Let me know if this helps or you want more information
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Old 28th July 2008, 05:28 AM
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Re: What is Cgk? (Index of Testing Means Capability)

Does anyone have any contemporary information / comments on Cgk (Index of Testing Means Capability)?

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Old 28th July 2008, 09:44 AM
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Re: What is Cgk? (Index of Testing Means Capability)

There is not much information available on this topic, which means that it never really took off.

The short story is:

Cg = 0.2 * StDev(Process) / StDev(Gage)

and

Cgk = [3 * StDev(Process) - |Bias|] / [3 * StDev(Gage)]

Cg is really rendundant if you have %GRR. It adds no new information, just packages it differently. Cgk is only of use if you did not establish credible calibration acceptance limits. If that was done, Cgk adds little value.

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Old 28th July 2008, 10:02 AM
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Re: What is Cgk? (Index of Testing Means Capability)

There is some info on CgK in one of the older posts - Cgk - The Kolmogoroff Method

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Old 28th July 2008, 10:49 AM
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Re: What is Cgk? (Index of Testing Means Capability)

Ah..that was my first post at the Cove!

Miner is right. It is one way of calculating measurement capability index.
Also: MSA vs. Measurement Capability Analysis - What are the differences?

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Old 28th July 2008, 10:56 AM
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Re: What is Cgk? (Index of Testing Means Capability)

Quote:
In Reply to Parent Post by Atul Khandekar View Post

Ah..that was my first post at the Cove!
Miner is right. It is one way of calculating measurement capability index.
Oh, you still remember it

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