[To...] Posted May 8, 2019 Share Posted May 8, 2019 We're looking at a job where the tightest feature tolerance is +/-0.040mm. The customer is requiring that we hold a 1.67 cpk. Does anyone have a calculator or formula where we can determine what the manufacturing tolerance (ucl/lcl) would need to be to hold the 1.67 cpk? I understand this technically requires actual data but we don't even have the job. We're just trying to determine if we should take the job. Link to comment https://qualityforum.zeiss.com/topic/18648-estimating-cpk/ Share on other sites More sharing options...
[De...] Posted May 9, 2019 Share Posted May 9, 2019 If I've followed the information on the following link correctly ( http://www.qualityforumonline.com/forum ... s-cpk.624/ ), you should have available ±0.024mm. 1/1.67*0.04 (0.02395). Link to comment https://qualityforum.zeiss.com/topic/18648-estimating-cpk/#findComment-105016 Share on other sites More sharing options...
[To...] Posted May 10, 2019 Author Share Posted May 10, 2019 Thanks Dean, If I read the forum posts completely, it appears the calculation you showed would be for cp? Or, did I miss something? Link to comment https://qualityforum.zeiss.com/topic/18648-estimating-cpk/#findComment-105018 Share on other sites More sharing options...
[De...] Posted May 10, 2019 Share Posted May 10, 2019 Tom, you are correct, that is for Cp, I do apologize. The Cpk would need to take into account how well your process is centered. If you take into account your normal machining variations, you should be able to work backwards and find a workable control limit for production. Link to comment https://qualityforum.zeiss.com/topic/18648-estimating-cpk/#findComment-105020 Share on other sites More sharing options...
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