Funky TP Callout

[dccfreak]

The print I have attached shows a few issues regarding GD&T.

1. Is the Datum structure and the way it is to be used to align. I brought this one up the other day.

2. The true position on the holes, doesn't seem to make a lot of sense to me regarding the way they are supposed to relate to the datums.

I basically know what the customer wants, but, I would like to incorporate some logic into that my mind comprehends in the way of my CMM. For some reason, things just don't seem right to me. I am just fishing for some ideas.

Thanks all
Brad

[Schrocknroll]

The 2 slots called out to -A- only would be essentially perpendicularity, this has been discussed many times before.

The part I'm confused with is that I see -C- datums called out, but no features referenced back to -C-. Also I see basic dimensions between the holes and the slots, but the only TP call out is to -A- and -B-, which wouldn't tolerance the basic dimensions from side to side.

Either there's more to the print or I'd agree that that's some funky callouts.

[Jan d.]

1. I think I understand the datum structure. Datum A establishes the plane (3 points), datum B sets the orientation (2 points). That is not really a problem.
2. The thing that I do not understand is the virtual condition on datum B in your call-out 11. I do not think that can be done.
Also, call-out 3, although strictly taken correct, is also strange because it only ties it to A.

Piece of advice: if you have the stomach to try it, the new dimensioning in V4.1 (XactMeasure dimensioning, as it is called in PC-DMIS V4.1) is sweet for problems like this. And after a lot of trial and error, I think it is pretty robust too!

However, be careful with the VC on datum B. I think that is something that PC-DMIS does not do right. However, I am still debating this with them.


Jan.

[Paul Sarrach]

For the Datum Scheme, They should have used target -A-'s instead of the Datum -B- call out, The two Datums -C-'s are really, the hole is Datum -B- and the slot is Datum -C- So level to -A- & -B-, Origin on hole and Rotate to slot.

And yes, the TP is all screwed up too. Who did this one print, was this some High School project?

[dccfreak]

Thanks for the replies.

I figured out for the most part concerning the alignment, however, I didn't level on both A & B. Paul, can you splain that one in a little more detail?

I basically leveled A, rotated slot, used B to let PC-DMIS know hole was relative to this surface, then I set the origin (x, y, and z) on the hole. I played around with best fits and such, and even iterative, but stuff didn't make sense still when trying to use both surfaces to level.

I would appreciate any further explanation on that one. I have attached a shot of my current alignment.

I am going to do the TP's against the datum scheme and just get r done, someone understood this, there is a rather nice gage built for it.
Thanks
Brad

[Paul Sarrach]

I disagree with your current alignment. I would use an iteritive alignment I would take points on -A- and -B- and level to them. Rotate from -C- hole to -C- slot, and make origin to the -C- hole. And leave it in body position and do my Tolerancing from there. If you do not use Datum -B- as part of your leveling you are not going to get the correct results.

Why don't you get a hold of them and have them explain their print.

[tking]

2 datum -c- (WTF?)

Max material modifier on -B- , a surface (another WTF?)

Yuk,

TK

[kbotta]

-B- is not a FOS. -C- is shown 2wice (hole and slot) and a datum symbol is used on both. That is a no-no. Datum targets should be used to define the features, and the symbol ( whish is identifiing the datum axis) should be related to 1 feature only. Although it can be shown as many times as nec. to provide clarity.
Also, the boundary position is incorrect.
So, yes - both of those FCF are either incomplete, or incorrect - whatever way you want to look at it.
b-rad

[dccfreak]

My alignment is simulating the position the gage was built in. That is why I did it like that cause that made sense to me.

Iterative was my first choice, but, if I leave it in body axis I can't dimension the part in accordance with the print. That is why I was trying to figure out what I could use as my final, and thus why I tried to align it like the gage.

I am pretty much on my own where trying to get information from the customer is concerned. It takes like 3 or 4 weeks to get your request far enough into the organization for anyone that cares to give you an answer. I need to have this done by tomorrow. I don't even have hole coordinates for body axis, usually I have them.

Wish I had a laser, that would be cool......