seems mainly inside of loops that they change on their own....
very frustrating when you don't see red but you may actually be out of tolerance because the nom changed its mind
3.7 MR2
bob
There are several recent threads about this that you should search out. I believe the general concensus is that the most common cause of nominals changing is an alignment that does not constrain all 6 degrees of freedom. If you leave some freedom available you are just inviting the PC-DMIS background editor to jump in and start making changes, and it does.
Sometimes you might not need to constrain all freedom (on round parts where angular orientation of features does not matter, for example) but you still need to do it to keep Pc-DMIS happy. Sometimes you might need to create a few generic features to make this possible if you don't have physical features to use in the alignment. For example, I always create an XY plane, an X-axis line, and an origin point at the beginning of the program.
If I want to create an alignment that simply levels to a measured plane and I do not care what the rotation angle or the origin are, I level to my measured feature and then use my X-axis line and origin point to complete the alignment. It doesn't matter to me one way or another that I am oriented perfectly along the x-axis but Pc-DMIS cares and this should stop most incidents of automatically changing nominals.
There is a setting in the settings editor that also might have an affect on this. You will find reference to that in other posts. There is also a file that, when corrupted, can cause odd behavior with best-fit alignments and result in changing nominals. I doubt that this later one is your issue but it has been mentioned as one possible cause in some situations.
I have held myself to a rigid discipline of full alignment everytime, no matter what, and have not had any further trouble with this issue.
Hope that helps.
There are several recent threads about this that you should search out. I believe the general concensus is that the most common cause of nominals changing is an alignment that does not constrain all 6 degrees of freedom. If you leave some freedom available you are just inviting the PC-DMIS background editor to jump in and start making changes, and it does.
Sometimes you might not need to constrain all freedom (on round parts where angular orientation of features does not matter, for example) but you still need to do it to keep Pc-DMIS happy. Sometimes you might need to create a few generic features to make this possible if you don't have physical features to use in the alignment. For example, I always create an XY plane, an X-axis line, and an origin point at the beginning of the program.
If I want to create an alignment that simply levels to a measured plane and I do not care what the rotation angle or the origin are, I level to my measured feature and then use my X-axis line and origin point to complete the alignment. It doesn't matter to me one way or another that I am oriented perfectly along the x-axis but Pc-DMIS cares and this should stop most incidents of automatically changing nominals.
There is a setting in the settings editor that also might have an affect on this. You will find reference to that in other posts. There is also a file that, when corrupted, can cause odd behavior with best-fit alignments and result in changing nominals. I doubt that this later one is your issue but it has been mentioned as one possible cause in some situations.
I have held myself to a rigid discipline of full alignment everytime, no matter what, and have not had any further trouble with this issue.
Hope that helps.