Is this datum callout legit?

[d.evans]

I am about to inspect these parts, but the -B- and -C- datums have me scratching my head.

[#2#]

That is a little strange.

Level A, rotate to the centerline of B, transfer axis to A, transfer axis to centerline of B, transfer axis to centerline of C.

[Jan d.]

This is odd. Level to A, but what to do with B and C?

Can you get the fixture from manufacturing in which they make this part? See how they hold it. What are the hard points, where are the clamps. Follow what they do in mfg. This may not be right, but in this case I think you are better off to just do what they did.

This is very ambiguous. I have never seen this before.


Jan.

[bw_bob]

Setting up the part per the Datum callout does not look to hard. Holding or fixturing the part so you can measure looks like fun. Not a very big part. Enjoy

[bob mappes]

pretty common callout here in wafer valley

they want the center of the part as your datums B & C
you can do this easily with pcdmis

create a mid-line between the two sides
create a mid-point between the two arcs

this will now be your center
with the mid-line also being your rotation of your alignment

so your alignment would be something like this

level to top surface
rotate to mid-line
topsurface is z zero
mid-line is x zero
mid-point is y zero

good luck

[Rich P]

Basically the centers of OD of the part as a slot width B datum and length C datum
B and D center points become your origin

Bobs way will do it

[d.evans]

Thanks all.

I went to the engineer, and he agreed with what you all have said. It is tiny though. Looks like it has an appointment with Mr. Sticky Tape. That will be the only option I have and still get to the features.

Bye.

[bob mappes]

try using hot glue to hold it

put a dab on a 1-2-3 block and press it on it while still hot

you want the datum a to be up so you can check most of it from there

[Sl33stak]

I know this is an old post but it applies to part I just checked. My question is WHY dimension it this way? I'm obviously not an engineer so I can't "think" the way they do.

[JCLASTOUTLAW]

Easy money I do agree datum B is used as a 2way in this datum scheme Ull have that. Good luck JC

[WithinU]

I know this is an old post but it applies to part I just checked. My question is WHY dimension it this way? I'm obviously not an engineer so I can't "think" the way they do.

That's exactly why, they don't think the way everyone else does.

As a programer, I would probably either, one, sent the print back to them and asked for a updated print, or submitted an Engineering change order, if that's what it is called there, or checked it to the functional/critical features, and marked up a print. Then submitted all the information to them.

I would also check it my marked way, and their way, just to see any differance.
But yeah, i have seen some pretty messed up callouts, and I have to stop and ask the same question, why?

[vpt.se]

It needs to fit in/on the counterpart, perhaps?

Would probably be better to use a profile tolerance and use the holes as datums, though.

[keego]

Looks fine to me. The only thing is for datum -C- I would use tangent points on the 2 radii (tangent to datum -B- midline), and use a midpoint of these 2 points as my origin. So level to -A-, rotate to -B-, set origin xy to -C- and z to -A-.

[lambo]

It looks legit to me due to the simplicity of the part.
Normally, major machined datum(s) tied to raw material/casting as your starting point(s), in this case almost all of the machined features on this part are used to establish part coordinate.
You can either dimension casting features to the part coordinate or machined features to casting coordinate, the sketch is simple, easy to understand, it’s symmetrical all around and everything is covered, it’s a smart way to dimension it (IMO).