Using cast hole as a datum

Can you use the hole as a datum feature, simply I'd think so but if it has draft that may complicate things.

If you want the other features centered on the hole regardless of feature size then just making the hole a datum feature and invoking it Regardless of Feature Size (i.e. no circle m next to that datum in the Feature Control Frames) should achieve that.

By the way, you need 2X on the 63 & 66 dimensions or else extend the leader lines. Also you don't need the 33 & 31.5 dimensions if using appropriate GD&T controls on the hole locations.

So would I just put the datum leader on the edge of the hole?

As for the dimensions, the 33 and 31.5 dimensions locate the bolt holes with respect to center hole. If I take those away, isn't the pattern just a free floating rectangle, then?

Thanks!

Not if they are controlled to the center hole datum.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

Raddy13,

A crude rule of thumb in fixture design is that the fixture must be ten times more accurate than the thing being measured.

If you are using a feature of size (FOS) as a datum, it helps if the FOS is something accurate. A fixture that picks up an FOS casting will not be accurate or repeatable. Maybe, you can tolerance the sloppy datum!

I strongly recommend defining datum targets on your casting. If you can mould them into casting, so much better. With datum targets, you do not care how inaccurate it is. You do not care that flat faces are not flat. Everybody in the process is working off the same repeatable datums.

--
JHG

Look at recent thread1103-366654 regarding whether or not you need 33 & 31.5 dims.

KENAT, please forgive my ignorance, I thought that if the holes appeared to line up and there was no other indication they don't, then the one dimension governed both holes. Why do you need to extend the leader lines of add the 2X. Is that is the standard? If so, where?
Thanks,

Do you have surface roughness (cast finish) called out?
A rough cast could throw off your hole positions.

Chris, CSWA
SolidWorks 14
ctopher's home
SolidWorks Legion

I'm with KENAT on this...
The basic dimensions are defined in the standard as being located per the feature control block, but an assumption would have to be made as to which features are being controlled without extending your centerlines or adding a qty to the dimensions.
I don't think extending your feature centerlines vs qty is addressed directly in the standard, but to eliminate any assumptions one or the other should be done.

“Know the rules well, so you can break them effectively.”
-Dalai Lama XIV

I'm with KENAT and ewh. The multipliers are required on the dimensions or you need extension lines.

But to handle the main question, try post the thread where Jim Sykes GDTP-S provided methods of using a tapered hole as a datum.




Tunalover

As far as I can see from a quick look at ASME Y14.5M-1994 this specific issue isn't addressed as such.

I'd perhaps fall back on what is said in 2.7.3 but that's perhaps a little weak in this case.

OK, thanks a lot. It looked redundant to me, but I can see that a assumption must be made.