Curved feature as datum

[dthom0425]

Hi all,

Attached is a very simplified model of a curved part I have. The curved part mounts on a cylindrical surface, no separate alignment features other than the clearance holes in the part.

I'm curious as to your thoughts on the best way to apply datums to this part. Functionally, I care that the holes are oriented to the central axis of the curvature.

I was going to make my primary datum the bottom curved face, and the pattern of holes datum feature B thus locking this part in all DOF. From there, the remainder of the feature (which a bunch are not shown) would be back to A|B(M).

Does this sound like an acceptable method? I assume the curved surface as a datum feature may cause some heartburn if you were trying to hard gauge it but a CMM may be able to do this?

Thanks for you insight.

 

[Tarator]

Please note the difference between

A | B(M)
and
A [BSC] | B(M)
and
A (M) | B(M)

You may want to consider the last two.

Please also note that the primary datum will be a plane, not an axis. So you will have to show your plane on the drawing!

Thanks.

 

[drawoh]

dthom0425,

Is your primary curve a cylindrical radius?

If so, I would use that as my primary datum, one end would be my secondary, and my tertiary datum feature would be the outside width, which I would call up at MMC. Bending is not an accurate process. I would slot those holes.

I assume this is not a precision part.

--
JHG

 

[dthom0425]

The primary curve is indeed a cylindrical radius.

The part is not formed. The picture is misleading as it is heavily defeatured....the full detailed part is machined.

Curious why the width of the part would be a datum feature? Functionally, the part is free to move within the clearance holes...there’s no surrounding structure that it mates up to.

 

[3DDave]

Do you care where the outside is located relative to the holes? If so, identify the outside surfaces as datum features or identify the holes as datum features and use the appropriate control to locate the other or just use the cylindrical surface as the sole datum feature and depend on simultaneous requirement by using position and profile geometric characteristic controls and refer only to that cylindrical surface datum feature.