NDC relates which type of MSA Study

B

BigTel

#1
I am looking for some help regarding the NDC (Number of Distinct Catagories) number.

My question is, does the NDC relate to all types of MSA study? So far I have seen it used on a type 2 sudy where you have 3 different operators obtaining results. But what about type 1 study etc?

Thanks for your help.
 
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Miner

Forum Moderator
Staff member
Admin
#2
ndc is a metric used specifically for assessing the gauge's suitability for SPC. While it may be calculated for a Type 1 study, unless all of your SPC is done by a single operator, doing so would be misleading. I do not recommend it.
 
B

BigTel

#3
We have been asked to look at it as part of our TS16949 assessment.

I have previously only performed type 1 studies to assess the variability of a gauge but I am trying to assess how to (and if I need to) add the NDC calculation into my workings. And what it will give me..!
 

Stijloor

Staff member
Super Moderator
#4
We have been asked to look at it as part of our TS16949 assessment.

I have previously only performed type 1 studies to assess the variability of a gauge but I am trying to assess how to (and if I need to) add the NDC calculation into my workings. And what it will give me..!
If you have access to the AIAG MSA manual, ndc is addressed on pages 44-45 and 117. Page 117 provides the fomula for calculating ndc.

ndc is expected to be greater than or equal to 5.

Stijloor.
 

bobdoering

Stop X-bar/R Madness!!
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#5
If you have a valid reason for using a type 1 study (automated gaging with no operator intervention), then ndc is evaluated with the same equation as a type 2 study.

AIAG recommends ndc>=5, however that is only applicable for standard product acceptance usage. For SPC ndc>=10.

To answer "what will it give me?" is an estimate of the statistically significant resolution of the device, under the GR&R test conditions.
 
B

BigTel

#6
I have a torque tester which checks the torque produced on a range of air driven screwdrivers. I have capability studies on the drivers but I am trying to do an MSA study on the torque tester itself.

I am using a spread sheet taken from this forum and I am getting an NDC of 0.74..! (My GRR result is 0.099 which leads me to belive I am doing something drastically wrong)

I have used 3 different operators to gain results from the same torque driver, used on the same static torquing point. Have I done something wrong here?
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#7
I have a torque tester which checks the torque produced on a range of air driven screwdrivers. I have capability studies on the drivers but I am trying to do an MSA study on the torque tester itself.

I am using a spread sheet taken from this forum and I am getting an NDC of 0.74..! (My GRR result is 0.099 which leads me to believe I am doing something drastically wrong)

I have used 3 different operators to gain results from the same torque driver, used on the same static torquing point. Have I done something wrong here?
Probably not. But, if you can upload your completed GR&R data sheet so we can look at it, we may be able to help you find some direction as to where the issue is. Also, if you have any manufacturer's specification for the torque tester (accuracy, etc.), that would also be handy.
 
B

BigTel

#10
Our torque guns have specs such as 4 to 4.5 NM, or 4.5NM +-0.2

I do understand that I really should be using something with a higher accuracy to do these checks, but I have to use what I have available.!
 
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