Question: Cg/Cgk formula

#1
Hi everyone, I’m performing Type one Gage on some control we have in the machine.
The first part of the machine has two control that do the same type of control so I will be performing the Gage R&R with the two controls as appraiser.
All the product that comes from the first part is controlled in the second part of the machine in which there is only one control. So, I’m thinking to do the type one Gage on this control (as suggested here).

I’m studying this type of gage (very thank to the cove!) and there is one thing I cannot understand well:

Why, as guidelines, we should calculate Cg/Cgk using 20% of the tolerance? Because to me it seems very narrow, but I don’t know if I’m missing some important concepts that don’t let me understand well.

Here an example of our process:

The control I’m studying is on the total length of the product. We have 10mm +/- 0,5 as specification limits. In the machine we set narrower limit +/- 0,45. Our range is basically 0,90 à 90% of the real tolerance.
Using 90% of the tolerance seems extreme but, to me, also the 20%.

So, I would like some more detailed explanation to “customize”, the better I can, this parameter to our case, please.
Thank you for the support in advance and sorry for my English, hope it is clear.

Edit: cannot really understand what add the two %Var. Since they are calculated as K/Cg or K/Cgk i don't know what they can possible add (K from the Cg formula ((K/100)*toll)/6Sd)
 
Last edited:
Elsmar Forum Sponsor
#3
I don't fully understand your measurement process, but I can explain where the 20% came from in the formula for Cg. The idea is to be able to compare the obtained Cg result with the expected process capability (Cp or Pp depending on the client). For example, if you expect the process to have a capability of 1.33, then when you get a Cg of 1.33, then you can say that the observed repeatability of the measurement is no more than 20% of the total process variation (which, again, is used for Cp/Pp calculation).

This means that this statistical assumption (20% of tolerance) cannot be compared with the narrowed specification limits (also 20%) that you apply to product qualification. These are 2 different things.
 
Thread starter Similar threads Forum Replies Date
T Question for: Cg & Cgk calculation General Measurement Device and Calibration Topics 3
M MSA question on Cg and Cgk Calculation Method and Type of Test Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
Ed Panek Calibration question Manufacturing and Related Processes 4
M Class Exempt Medical Device Recall Question US Food and Drug Administration (FDA) 3
sonflowerinwales Metric or Imperial; that is the question... After Work and Weekend Discussion Topics 6
M Can someone help me with this CMM programming question? Manufacturing and Related Processes 2
A A strange question about predicate device selected in 510(k) submission Medical Device and FDA Regulations and Standards News 8
S Question regarding AQL - ISO 3951 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
D Document Control Question involving DocuSign US Food and Drug Administration (FDA) 6
JoeRandom11 Question about Customer Supplied Equipment AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
M ISO 13485: 2016 Lot numbering question ISO 13485:2016 - Medical Device Quality Management Systems 4
S Nadcap - Heat Treatment Proof of Verification question for Digital results AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
JoeRandom11 Question of Calibration Cycles AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 8
D Software Validation Question ISO 13485:2016 - Medical Device Quality Management Systems 10
B 8.5.1.1 Control Plan - question audit NC IATF 16949 - Automotive Quality Systems Standard 5
C Document Identification Question ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 8
D Question regarding PCR workstation Fume Hood upon first use ISO 13485:2016 - Medical Device Quality Management Systems 0
Moncia ISO 9001 calibration question please ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
Q Quick question on the sequence of ISO 17025 external audits ISO 17025 related Discussions 14
D ISO 13485--Question regarding performing calibrations in house. ISO 13485:2016 - Medical Device Quality Management Systems 13
S Document numbering question? ISO 13485:2016 - Medical Device Quality Management Systems 7
J Has the facility been inspected? question in Certificate to Foreign Government application Other US Medical Device Regulations 0
M ESTAR 510(k) submission question Medical Device and FDA Regulations and Standards News 0
J Question on clause 5.2.2 IEC 62304 - Medical Device Software Life Cycle Processes 2
Ed Panek ISO 15223 Question EU Medical Device Regulations 2
J Quick question on responsible person's experience requirements UK Medical Device Regulations 3
J PFMEA/control plan question- PLEASE HELP ! IATF 16949 - Automotive Quality Systems Standard 8
3 Scope question ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
L Question regarding "Customer Property" AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 11
T Noob question regarding sample size Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
K 510(k) Manufacturer question (private label and manufacture under another persons 510(k)) US Food and Drug Administration (FDA) 1
M Question About Rolled Throughput Yield Manufacturing and Related Processes 5
M Quick Gage R&R Question Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
S Question: Best alternatives to audits for ensuring compliance Quality Tools, Improvement and Analysis 5
Ed Panek Question from 13485 Auditor ISO 13485:2016 - Medical Device Quality Management Systems 2
C Question on KAFO (Knee Ankle Foot Orthosis device) classification CE Marking (Conformité Européene) / CB Scheme 0
T BMW GS 93010-2 Question Various Other Specifications, Standards, and related Requirements 1
S FDA 510(K) submission question US Food and Drug Administration (FDA) 4
Ron Rompen Question regarding CMM probe damage General Measurement Device and Calibration Topics 4
T FDA UDI Question - Class II Medical Device Other US Medical Device Regulations 2
C Complaint Return Sample Size Question 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 4
8 Drawing Feature Question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 8
D Question: How to analyze numerical and attribute data Reliability Analysis - Predictions, Testing and Standards 11
D Question on electronic signatures and initials on batch records ISO 13485:2016 - Medical Device Quality Management Systems 4
A Special Characteristic question from Automotive CSR Customer and Company Specific Requirements 9
Ron Rompen GDT Question - is this even correct? Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
A PPAP question for audit APQP and PPAP 17
C ISO Question - Do you say "I-S-O" or "I-Soh"? Misc. Quality Assurance and Business Systems Related Topics 14
D Question regarding where "validations" fit according to ISO 13485:2016 ISO 13485:2016 - Medical Device Quality Management Systems 1
D Question on Supplier Quality (SCAR) ISO 13485:2016 - Medical Device Quality Management Systems 6

Similar threads

Top Bottom