Capability for CMM Scanned Profiles on a feature with a Bilateral Profile Tolerance

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M

Mr.Happy

#13
Re: Capability for CMM scanned profiles on a feature with a bilateral profile toleran

Gould you post the data in a Excel sheet so we can play with it in order to help you solve this problem.
 
J

JAltmann

#14
Re: Capability for CMM scanned profiles on a feature with a bilateral profile toleran

For what your trying to do you'll really want to use single vectored points, and not a line scan as is currently being perfomed. This will allow you to compare the exact same points for trends/fliers ect.

One down side with scanning like this is that you end up with "fliers" in the data. Sometimes dues to controller errors, they are minimal and could possibly be eliminated or greatly reduced with filters.

Any issue that needs to be understood is how repeatable the alignment system being used is. This can be checked easily by loading, running, and unloading the same part thru multiple runs and looking at this repeatability. If you have high repeatability values this will cause other errors with the SPC study in the way of poor results.
 
R

Rand T

#16
Re: Capability for CMM scanned profiles on a feature with a bilateral profile toleran

Here is part of a spreadsheet with the data for feature #12
 

Attachments

R

Rand T

#17
Re: Capability for CMM scanned profiles on a feature with a bilateral profile toleran

For what your trying to do you'll really want to use single vectored points, and not a line scan as is currently being perfomed. This will allow you to compare the exact same points for trends/fliers ect.
I agree that this makes the analysis of a specific point easier, but from a standpoint of determining the profile of the entire part, the line scans are much quicker and check the entirety of the part.

Either way, I need to develop a strategy for capability using what data I have.
 
R

Rand T

#19
Re: Capability for CMM scanned profiles on a feature with a bilateral profile toleran

Are these several parts, in time order of production?
Yes, 34 pcs.

The data is the min profile, max profile, and the "measured" value which is merely the difference between the two.

Feature has 0.08 mm profile tolerance
 

bobdoering

Stop X-bar/R Madness!!
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#20
Re: Capability for CMM scanned profiles on a feature with a bilateral profile toleran

Here is the analysis I made based on your data. If you plot the difference from min to max, you are always going to have a positive value. Your lower limit is zero. I used the .08 as your tolerance, since it is the width of your profile zone, and 0 as your minimum (also identified as a boundary, since you can not go below it.) So you compare your zone usage to your total zone tolerance for capability - and if you do that, you get the attached results. Note that it is a non-normal distribution (used weibull as the distribution) since it is physically unilateral. Also, being non-normal and unilateral, Cpk and Ppk really don't apply - but are estimated for academic discussion.

This may not be my "final answer", but I provide it as a starting point for discussion.
 

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