Measured values change using MMC

[rerun_lives]

When I try to Dimension a circle for true position and try to apply MMC from two other Datum features my True Position Deviation keeps coming up with a value of 0.0000. My Nominals do not change and the bonus values don't add up correctly. Are they being compensted for because of more than one datum feature is being used?
Do I have to execute the feature again after I tolerance it? ANY CLUES?
version 3.7 MR3

[Matthew D. Hoedeman]

MMC WITH Datums has been a bug-a-boo for a long, long (extra long) time. Unless you absolutely need the MMC of your datums, do NOT use datum's as part of the dimension. The best way to do it is to make an alternative alignment using the datums for that feature, then do the TP/MMC dimension to the alternative alignment. If I have to do this, I always to it at the end of the program. Also, do NOT forget to 'recall' your main alignment afterwards.

[Mike N.]

When I try to Dimension a circle for true position and try to apply MMC from two other Datum features my True Position Deviation keeps coming up with a value of 0.0000. My Nominals do not change and the bonus values don't add up correctly. Are they being compensted for because of more than one datum feature is being used?
Do I have to execute the feature again after I tolerance it? ANY CLUES?
version 3.7 MR3

I have been told that ver3.7mr3 uses "fitting" to adjust the temporary alignment created when using the checkbox "use datums". That version will do both rotation and translation to fit that feature into its zone. It must be the case where you have enough tolerance on the datum features that allows the feature in question to "appear" perfect for postition after all the fitting.

Make sure that your datum features have the correct nominals and tolerances before using the "use datums" function.

[craiger_ny]

MMC WITH Datums has been a bug-a-boo for a long, long (extra long) time. Unless you absolutely need the MMC of your datums, do NOT use datum's as part of the dimension. The best way to do it is to make an alternative alignment using the datums for that feature, then do the TP/MMC dimension to the alternative alignment. If I have to do this, I always to it at the end of the program. Also, do NOT forget to 'recall' your main alignment afterwards.

Matt is right it has been bad juju doing the MMC on datum thing but there is a way around it. This is my solution to what you might be going through. You can TP your featueas and put a material condition modifier on your datums minus the bug. If this is in fact your problem.
http://www.pcdmisforum.com/showthrea...nks+craiger%2A

Craig

[Tested]

I have found that I can put the deveations of my DATUMS into a assignment, and use these plus my tolerance inplace of my tolerance. You must create a function to do the math for each one. This works well but unless you have 3 or 4 that go back to the same DATUMs it might not be worth the time. Also you will be in RFS and if others are looking over your reports you'll need to inform them. Sometime just a comment will work to explane what you have done.

[Dave Chronicle]

When you "Use Datums" , PC-DMIS does a fitting type true position, which tries to simulate a hard gage. Refer to Wilcox's site @ the http://www.wilcoxassoc.com/Downloads...ionalfiles.htm
for info on true position and how it works in PC-DMIS when you "Use Datums" and use an MMC on a datum. Thats how the feature can be perfect but have locations move on you. The "pins" of the gage are moving around to make that hole perfect.

[djayne]

This subject has come up before and I used Craig's method for TP and bonus and it works great. It's hard to believe that the Wilcox engineers cannot incorporate this into the software.