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  Statistical Techniques and 6 Sigma
  Need sampling table for in-process inspection

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Author Topic:   Need sampling table for in-process inspection
bimco
Lurker (<10 Posts)

Posts: 1
From:Sheridan, IN, USA
Registered: Aug 98

posted 28 August 1998 05:03 PM     Click Here to See the Profile for bimco   Click Here to Email bimco     Edit/Delete Message   Reply w/Quote
I'm looking for a sampling plan/table to determine sample size and inspection frequency based on a given rate of production. For example, a process produces 500 pieces. How many pieces should be checked and how frequently?

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Marc Smith
Cheech Wizard

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From:West Chester, OH, USA
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posted 28 August 1998 05:37 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
If you're looking for an AQL (Acceptable Quality Level), why not use the old Mil-Std-105? It's technically a canceled document (as is the way with many old military specs) but you can still use it. I know an organization 'took it over' but I can't remember who it was.

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Don Winton
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From:Tullahoma, TN
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posted 21 September 1998 05:36 PM     Click Here to See the Profile for Don Winton   Click Here to Email Don Winton     Edit/Delete Message   Reply w/Quote
bimco,
I agree with Marc. Even tho MIL STD 105 is discontinued, the OC's and sampling plans are still statistically valid. Use these as a good guide. I recently received a post that gave guidance as to sample sizes:

n>=((Za/2*sigma)/E)^2 wher Za/2 is (1-confidence(i.e.0.95))/2. Sigma is standard deviation of the data and E is the expected Error. This is also considered the difference between the mean and your sample and the mean (estimated, maybe) of your population.

I have another equation somewhere (?) and will also try to forward this one as well.

Regards,
Don

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Marc Smith
Cheech Wizard

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From:West Chester, OH, USA
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posted 04 July 2000 01:38 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
From: ISO Standards Discussion
Date: Mon, 19 Jun 2000 11:26:19 -0500
Subject: Re: MIL-STD-105D /Khan/Westall

From: "Greg Westall"

FYI
MIL-STD-105D was revised to MIL-STD-105E May 1989 and was canceled Feb.
1995. Suggested replacement is ANSI/ASQC Z1.4

As far as a 1 page plan, I have never seen one that covers all AQL's and
Inspection Levels.

Greg Westall

<< From: "Jawad Khan"
I am looking for a one page matrix with sampling plan per Mil-STD-105D.
Can anyone send me this page? >>

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Marc Smith
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From:West Chester, OH, USA
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posted 04 July 2000 01:45 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
From: ISO Standards Discussion
Date: Tue, 20 Jun 2000 09:31:33 -0500
Subject: Re: MIL-STD-105D /Khan/Westall/McElhiney

From: Larry McElhiney

>> From: "Jawad Khan"
>> I am looking for a one page matrix with sampling plan per Mil-STD-105D.
>> Can anyone send me this page?


I agree with what Greg says, however, many customers still have things written into their specifications like:

"All inspections will be accomplished using a Mil-STD-105D Level II 1.0 AQL (single normal)"

It is difficult to change their conceptions when we are really only talking about a statistically valid sample plan.

When we were using a C=0 plan, it was referenced to a similar plan as above, but our customers had no trouble accepting it even though it was to the "D" revision because it was, in fact, statistically valid.

Many companies still use a single page sample plan wherein they have a fixed lot size which draws them to a fixed sample size for a given AQL--this is extracted from the appropriate standards and issued by the Quality Engineer to the appropriate work areas. Since the QE can always show how the single page plan relates back to the standards, I have rarely seen it as a problem.

I think that this is the sort of support that Mr. Khan is requesting.

Just my opinion.

Larry

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Marc Smith
Cheech Wizard

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From:West Chester, OH, USA
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posted 04 July 2000 01:47 PM     Click Here to See the Profile for Marc Smith   Click Here to Email Marc Smith     Edit/Delete Message   Reply w/Quote
From: ISO Standards Discussion
Date: Thu, 22 Jun 2000 11:32:23 -0500
Subject: Re: MIL-STD-105D /Khan/Westall/Melvin

From: "Pat Melvin"

Even though MIL-STD-105E was canceled and replaced, it may be located at www.variation.com/techlib/standard.html

This site also references the suggested replacement, associated ANSI standards, and ISO standards for Sampling Procedures

Pat Melvin

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