I can't say that I am seeing that not to say that I am not doing something wrong however. The one concern I have with that is, does it report the hole as being closer in each axis? i.e. on the report does it shorten the basic number it is reporting to compensate for the added tolerance?
I can't say that I am seeing that not to say that I am not doing something wrong however. The one concern I have with that is, does it report the hole as being closer in each axis? i.e. on the report does it shorten the basic number it is reporting to compensate for the added tolerance?
It will do so in the amount and direction that it was able to shift the part and stay on the pins.
ONE THOUGHT! I heard someone say that if a hole is OVER SIZE (bigger than it is allowed to be) that SOME versions of Pcdmis will NOT give you any bonus tolerance for that MMC, even though you SHOULD still get it. Being over-sized does NOT alter the fact that SOME of that size deviation is STILL your bonus.
I agree with Slesh and Matt: if you have virtual conditions on your datums, it becomes incredibly difficult to guess what your TP results will be. I tested 4.0 and 4.1 and I found short-comings. 4.2 was the first one where I started to trust the results. Hate to say this, but I think you need to upgrade...
The problem is, as mentioned before, that the moment you have virtual conditions on a datum, a hard gauge or attribute gauge is simulated. This allows for "wiggle" in the datum hole that has the VC, as hard gauges can be wiggled by hand to the best possible orientation (humans do this naturally, in computers it is he!! to calculate). The hard gauge becomes something of a go/no go situation. The gauge fits, or it doesn't.
When you have VCs on your datums, I have argued before that the actual number for your TP becomes un-important. I belive PC-DMIS ought to only report whether the gauge goes, or doesn't go. Because PC-DMIS gives a number, the SPC gods want to do process control on it, which is ludicrous in my opinion.
If you want to do process control on these types of calls, I analyze the call with NO VC on the datums. That gives you a singular answer and has direct meaning to the operator. Then, for part acceptance, you analyze the part with VC.
This can be quite interesting. You may have a part that is totally out control SPC wise, but may be perfectly acceptable because of the VC on the datums. I have had this many times. I accept those parts. But also report the SPC results so mfg people know that life is NOT as good as they think it is.
Thanks for everyone's input, you all have valid points. Personally I don't believe in allowing MMC to be calculated into the TP tolernace except in the event that product is beyond the specified tolerance as this gives me a "safety net" if you will before the need to non conform product, unfortunately I don't run the place and have bosses to answer to. I appreciate everyone's help as there seems to be very good information in this forum and look forward to you all for help in the future.
