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.
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.
