GRR for Coordinate Measuring Machine

Chris,
If you program your cmm for automatic programs (parts that are aligned using machine coordinates) or you auto align after manually touching off, then the operators shouldn’t make a difference. If it is a manual cmm then it is definitely recommended to use all three operators. All of our cmm’s are DCC and we auto align after touching off manually or program from machine coordinates because of a study that was done with only manual alignments. It showed cosine error does have a factor in your measurements. The tolerance of the products that you are measuring makes a difference in the decision of whether or not the cosine error is large enough to effect the outcome of your gage R&R. It is also recommended to place your parts in different area’s of the surface plate to factor in volumetric accuracy of your machine. (unless you use a safe plate and fixturing that always locates the part in the same area of your machine.) If you have any more questions we have a great staff of cmm programmers that would be more than willing to share their thoughts or idea’s with you. Please feel free to e-mail me at [email protected]

Chris
 
I would like to make two comments. The first being that one time I gave the same data to two different quality groups and one said that the gage was capible and the other said that it wasn’t. Different people have used different assumptions when developing the GR&R system and this can cause the results to be different. This could be a problem if you share the data with others.
 
My second comment would be that I have seen cases where the thing that “everyone” is sure couldn’t be the problem was. With my last company, in ten years no one had realized that there was an annual cycle to the reject rate. Once we discovered that, we tried temperature, humidity, and barametric pressure and didn’t get a correlation. We finally decided that it was the annual cycle that the managers went through.
 
David

Mike
 
Thanks for your post. Yours is a very good example. I expect that everyone that has been doing this for very long has an exmple but I thought it was worth mentioning to some one that seemed to be just getting started.
 
David