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Deming contrasted US and Japanese focus: spec limits vs variation. Here’s the essence:
“Hi, I’m Jay Arthur, author of “Lean Six Sigma Demystified” and QI Macros [software].
“I don’t know about you, but every once in a while I go back and read through books that I’ve gotten in Quality over the years. I went back into Deming’s “Out of the Crisis.” It was very interesting. There’s a thought he put in here and I’ll read it to you: “We in America have worried about specifications: meet the specification. In contrast, the Japanese are worried about uniformity, working for less and less variation around the nominal value…”
“What does he mean?
Continue Reading "Deming on Spec Limits vs. Variation"
Posted by Jay Arthur in Improvement Insights, Jay Arthur Blog.
A QI Macros customer called to ask how he could figure out the specification limits to give him a Cp/Cpk of 1.33. What’s wrong with this question? The answer is obvious isn’t it?
Continue Reading "Who Sets Your Specification Limits?"
Posted by Jay Arthur in Improvement Insights, QI Macros, Six Sigma.
Customer asked me what seemed like a strange question: What specification limits do I need to get a Cp greater than one? Usually her customer should set specification limits, but her boss wanted to know what they could deliver. Hmmmm!
Then I realized that since QI Macros templates (e.g., XmR chart) calculate the average and sigma estimator, the LSL/USL for Cp = 1.0 would be:
LSL = Average – 3*SigEst USL = Average+ 3*SigEst
For Cp = 1.33, just change the 3 to a 4; Cp = 1.66, change the 3 to a 5. Here’s an XmR chart template with some sample data and calculations to reverse engineer spec limits:
Continue Reading "What USL/LSL Do I Need for Cp>1?"
Posted by Jay Arthur in QI Macros, Six Sigma, Statistics.