More GD&T - We can't compute Cpk using GD&T

#1
Ok guys. This one really baffled me. I was in a meeting with our vendor when the program manager said. We can't compute Cpk using GD&T. (I have since convinced most of them that you actually can, thanks to everyone's input.) He then said but we can compute Cp. I have read some previous posts comparing Cp with Cpk. But I can't for the life of me figure out why you can't (or at least they say you can't) compute Cpk but can compute Cp. Are there any differences that would keep you from making the math work.
 
Elsmar Forum Sponsor
B

Batman

#2
Hi Tim!
GD&T is a common set of rules for creating a part drawing with form, fit, and function in mind. Every part has some limits above and below which you cannot go. These limits are called tolerances.

Cpk (and Cp) is a statistical calculation from [usually a sample of] the actual produced parts comparing that data TO the tolerance on the drawing.

In this order:
Create drawing with tolerances, etc.
Make parts to drawing
Analyze (measure) parts - compute average and sigma
Compare this calculation to the tolerance on the drawing.
 
D

Don Winton

#3
Are there any differences that would keep you from making the math work?
No there are not. Both equations use mean and standard deviation, along with constants (3, 6, USL, LSL, etc.) Since you can determine mean and standard deviation, if you can compute Cp on a variable, you can compute Cpk on the same variable.

Regards,
Don

------------------
Just the ramblings of an Old Wizard Warrior.
 
Thread starter Similar threads Forum Replies Date
K Gage R&R with more than 3 appraisers Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
K More than one importer for the same device EU Medical Device Regulations 3
S Two or more predicates suitable? 510K submission US Food and Drug Administration (FDA) 5
E Received a Major finding during IATF Surveillance audit for loss of BIQS Level 3 (more than 6 SPPS in 6 months)...how should we address SYSTEMIC CA? IATF 16949 - Automotive Quality Systems Standard 11
L Which one is more important for FMEA CC or SC, FMEA and Control Plans 6
M UDI-PI on a package that contains more devices EU Medical Device Regulations 3
M Informational Update – MDR and IVDR implementing measures rolling plan – 2 more NBs designated under the new regulations Medical Device and FDA Regulations and Standards News 0
B More than one Risk Report per Medical Device ISO 14971 - Medical Device Risk Management 3
Ed Panek Can a single supplier fit two or more categories for risk? ISO 13485:2016 - Medical Device Quality Management Systems 2
Sidney Vianna More allegations of unethical behavior in the Aerospace Sector AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
N Technical File Reviewer has requested more testing to ISO 10993 Other Medical Device Related Standards 10
M Informational FDA Panel: Too early to pull textured breast implants over cancer risk, need more data Medical Device and FDA Regulations and Standards News 0
M BSI – Want to know more about the Notified Body? Registrars and Notified Bodies 0
Marc Renewables, led by wind, provided more power than coal in Germany in 2018 Sustainability, Green Initiatives and Ecology 2
Marc Forums - "Watching" One or More Forums for New Threads and New Posts Elsmar Xenforo Forum Software Instructions and Help 1
A MSA When an Instrument Measures More than One Parameter Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 7
M Vernier Calibrations & more General Measurement Device and Calibration Topics 5
bobdoering Contingency Plans Likely to be Scrutinized More Now IATF 16949 - Automotive Quality Systems Standard 9
Q How can you justify using a more accurate Pin Gage class? General Measurement Device and Calibration Topics 16
JoshuaFroud Addressing wet ink signatures when more than one site is involved 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 8
G More on IATF 8.5.6.1.1 - Temporary Change of Process Controls IATF 16949 - Automotive Quality Systems Standard 4
Sidney Vianna IAF Ruling - No more ISO 9001:2008 nor ISO 14001:2004 audits after 2018-03-15 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
P Tool for Measuring - Do I have to do more than one Gage R&R for the PPAP? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
T ISO 14001:2015 cover more than 1 company or business unit? ISO 14001:2015 Specific Discussions 13
L How to get more Auditing Experience Career and Occupation Discussions 11
C Squeeze in one more - Rate of failure Statistical Analysis Tools, Techniques and SPC 6
M Is it possible to have more than one authorized representative in Saudi Arabia? Other Medical Device Regulations World-Wide 6
somashekar People are more than just ?resources? Book, Video, Blog and Web Site Reviews and Recommendations 1
ncwalker More Central Limit Theorem Questions Six Sigma 4
M More than canned audit check-sheets? Auditing the Engineering Department Process Audits and Layered Process Audits 5
Marc Explore - Movies, audios and more! An Online Library Coffee Break and Water Cooler Discussions 2
B Share ideas to make Management Review more interesting Management Review Meetings and related Processes 4
Wes Bucey More Phishing Emails! Coffee Break and Water Cooler Discussions 7
O Rebuilding Quality Manual to be more relevant to our business Quality Management System (QMS) Manuals 7
Stijloor Toyota recalls more than 6 million vehicles. World News 5
cscalise Separate Forms or Procedure Attachments - What's more common? Document Control Systems, Procedures, Forms and Templates 2
T Promotion with Less Pay and more hours Career and Occupation Discussions 37
S FDA CDRH Premarket Review Submission Cover Sheet - adding more products 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
T More than One Original Test Report - Original Print General Measurement Device and Calibration Topics 4
Hershal More about Teddy bears Coffee Break and Water Cooler Discussions 0
B Calculating Combined DPMO and Sigma Level for Two or More Different Work Areas Six Sigma 3
G More than one Marketing Authorization Holder (MAH) in Japan Japan Medical Device Regulations 2
M Is information required on more than one side of box? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
J Attribute Data MSA for more than 3 Operators Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
M ISO/TS 16949:2009 Follow-up Audit Visits to create more Revenue IATF 16949 - Automotive Quality Systems Standard 12
G Improve final GR&R value by taking average of more measurements? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 11
K Calibration Standards - Master weight having more tolerance than our gram scale General Measurement Device and Calibration Topics 3
S K-stand definition and more information about it Manufacturing and Related Processes 1
Q Dixon city comptroller ?misappropriated? more than $53 million World News 2
V Plotting MTBF for More Systems in a Single Chart using Meridium 3.4.2 Software Reliability Analysis - Predictions, Testing and Standards 2

Similar threads

Top Bottom