Can you make a slot symmetric to a hole?

[debun]

I need to locate a slot to a hole whats the best way to do it. The hole is datum C but the axis is perpendicular to the slot. Is it reasonable to do what I've done in the attached image?

http://files.engineering.com/getfile.aspx?folder=e54b8929-af4e-47fd-beb3-72e669a27f5d&file=gd&t.JPG

 

[greenimi]

Can't open the attachment.....

 

[drawoh]

debun,

Your datum features[ ]A and[ ]C work in the same direction. I would use a positional tolerance rather than symmetry. Perhaps you position your slot width to datum[ ]C, and make it parallel to datum[ ]A to some looser value.

--
JHG

 

[debun]

To use a positional tolerance to "C" wouldn't I need a dimension? The slot and hole are coaxial so the dimension would be zero. I'm not sure how to do what you are suggesting. You are correct about A and C working in the same direction but A is to locate the hole (C) and I need to locate the slot to C not A.

 

[drawoh]

debun,

No. You have shown both features on a centre-line. This is one of the benefits of GD&T positional tolerances, versus ±[ ]dimensions.

--
JHG

 

[debun]

I think I understand what you're saying but per ASME basic dimension must be used to establish true position.

 

[3DDave]

The attached file name has an "&" in it so it can't download.

They are not coaxial. Coaxial means "has the same axis" and there is only one axis. The tube and the slot do not have an axis.

If you want to have the slot to follow the holes, then make the holes the primary datum feature and the rectangular tube height the secondary datum feature reference.

A basic dimension of zero is implied by the use of an axis. It's one of the fundamental rules.

(k) A zero basic dimension applies where axes, center
planes, or surfaces are shown coincident on a drawing,
and geometric tolerances establish the relationship
among the features.

One thing that is missing is that neither the hole or slot are perpendicular to B.

 

[powerhound]

debun,

What you've shown in your original post is not correct. Some of the responses of others make me think there's another drawing that I just haven't seen. I'll comment on what I can see.

Since you're asking about the best way to do this, I would advise against using symmetry at all. The chances are pretty high that it's not really what you're after. Use position on both features instead. Depending on the function, you might be able to use an MMC modifier on it too.

As drawoh pointed out, A and C both constrain translation in the vertical direction but since A does it first, C doesn't get to so reference to C does nothing.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech