How to Determine CMM Gage R&R - Accuracy, Repeatability, Reproducibility?

R

rexbo

#1
Hello,

I'm just an end user of data coming from a programmable c.m.m. (Coordinate Measuring Machine). That is, one technician writes a program, and several operators use it to measure different parts, and they provide me the data. Now, I have reasons to question the data I've been receiving lately.

So, is there a quick and dirty way for a novice like me, to determine whether I should be confindent in this data? I can have some operators measuring different parts, and I have access to minitab.
Is this something that would help me reach an objective conclusion about data reliability?
How?
I'm looking for an accuracy of less than one thou.

Any constructive help will be greatly appreciated.

thanks,

rexbo
 
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W

WSICMM

#3
As both a CMM Programmer and an 'end-user' from others in my deptarment, there are a couple of things to consider:

1) is your CMM DCC? - that is (as the reference to the previous post states), does the operator(s) simply load the part and let the CMM to the work. If so, *and the program is correct in terms of datums/tolerances/etc*, then operator input (in my experience) is pretty much nulified...

2) do you get different readings off the same part using the same program?...if the above is true and you use a dcc machine, i suspect that these results will be very similar...although perhaps not as close as you need.

3) can you verify the parts using good-ole manual measurement tools (ie height-gauge / surface plate), or via an attribute checking fixture (gauge)?

It is important to note that the CMM is a measurement tool - and that not not every tool is best for every application...(read - shotgun to catch a butterfly)...accuracy of 1-thou will be dependant on several factors including temp, and especially set-up...

Also, if you apply the 10% rule, then you are looking for something in the neighbourhood of 1-tenth...which i'm noit sure the CMM can hold...your best bet would be to do an old-fashioned GR&R as mentioned in the post prior.

Hope this helps...

Aaron
 
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