setting specification limits

Six Sigma – iSixSigma Forums Old Forums General setting specification limits

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    Bruce Floyd

    Whether or not there is 100% inspection depends on the cost of failure.  One always works backwards.  Some processes are expensive because the cost of failure is very high.  There are many processes that run well withing 99.5% normally, but the user is not too picky either.  If dry wall screws have threads and are +/- 1/4″ in lenght, they work.  This is not true for bolts that must mate up with nuts. The allowable tolerances are much tighter.  One doens’t want wheels to be falling off of cars.  The cost of failure is very large.  Lumber tolerances are of the 4 sigma variety.  Ever laid floor joist where the overlayment does not rest on all of the joist?  The result is a squeaky floor even though the flooring system will not fail.  The lumber customer is happy, but the final user will never be happy.  The cost of failure is minimal.  That is why the variation exist. 

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