Position not updating.

[Peter DeGroot]

Hi Folks,

This is my first post here since the new forum, so here goes.

ONE machine with 3.7mr2 PH10T / TP20

I have a slot created using a CAD igs model and auto round slot. All is well. Nominals are good and everything works just like it's supposed to.

My problem is in the True Position reporting. The drawing uses a feature control frame TP - A @ max B @rfs C @ max. When I just use no datums the report shows the correct slot location measured compared to the nominals with the alignment on the correct datums. When I check the "use datums" box and add the datums and modifiers it reports the slot location exactly at nominal. X = 0 and Y = 0. If I turn off the use datums it goes back to the correct measured value.

I've proved it out using known good parts and known out of tolerance parts.

Why can I not get it to use the datums and get the bonus???

I have other programs with this same condition that work well. What setting must I change????

Thanks in advance. Peter DeGoot

[Matthew D. Hoedeman]

When you use the datums on TP, it is 'moving' the datums around in the background as much as it can to show the hole the best it can. So, if the hole is close enough to 'perfect' that the MMC bonus from the datums will let it sit at ZERO and still have the datums 'pip' in the background fixture, it will show it at zero. Yes, this really 's u c k s', I think the bonus from the datums' MMC should show up as BONUS in the TP dimension, but that is NOT the way they have it in Pcdmis. If you COULD also dimension the datums at the same time as this hole, you will find them NOT on zero, but within their MMC range.

[Wes Cisco]

There are probably 5 of us typing an answer to this right now. MMC on datums does not work for diddysquat in pc-dmis. IMHO. What is going on, is that when you select "use datums" and apply MMC to one or more of the datums you seleced, pc-dmis does a new "wiggle" alignment where it lets the datum "float" within tolerance to simulate a hard gage. The result is your tp is reported as 0.000 when you know it is not 0.000, but it is within the print tolerances. I think it should report the same deviation as if you did not check "use datums" but also show how much bonus you pick up from the datum seperate from how much you get from the feature itself, (if it is MMC). My own personal policy is that if it needs a hard gage, I have my shop make one. I rarely need see MMC on datums for the parts we make, and when I do, I rarely need the bonus. On those extremely rare occasions I do need the bonus, I calculate it by hand and put a comment box in the report. I believe CraigerNY posted a work around for this recently. Someone who needs this bonus more often may be able to give you a better solution, but hopeful I have explained what is going on. HTH.

[craiger_ny]

This is a lousy deal. If you need bonus here is a work around, yes this is a common gripe

http://www.pcdmisforum.com/showthread.php?t=714&page=2&highlight=thanks+craiger%2A

[Peter DeGroot]

thanks

thanks folks!