True Position Datum

[[La...]]

I do not remember ever seeing a True Position Datum called out like this (D-B), with D-B being in the same square, before. Both D and B are Planes. My only thought would be to use an intersection between the planes as the datum. So how is the correct way to apply this with Calypso?
Datum_D-B.doc

[[Br...]]

This is just taking multiple datum features and combining them as a single datum feature. This is mostly used to take two coaxial cylindrical datum features to combine them and create a single feature axis, or Co-planar Datum features, and treat them as a single plane. Sounds like you have the later but I can't see it on the picture you provided. If you have two planar datum features, just simply treat it as a single plane. In Calypso, you can either measure both in a single strategy with two different paths, or you can measure them as separate features and recall feature points into one single plane. If they aren't co-planar, it gets trickier.

Capture.JPG

[[Me...]]

Interesting callout. -D- is the primary and a co-secondary datum. Can't see the print, but I wonder how it's controlling translation twice? If -D- is controlling 3 DOF what DOF are D-B controlling?

[[La...]]

A Calypso view of the part.
Datum D is the larger face with the 4 threaded holes that are called out, and Datum B is the smaller face.

Datum_D-B-1.pdf

[[Me...]]

-D- constrains 3 DOF. B alone constrains the same 2 DOF as using D-B as co-datums. D does nothing as a co-datum. I don't get it. I must be missing something.

[[Br...]]

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Those datum features aren't co-planar. I cant really make much of sense out of it. Part of me thinks they just want Datum B to be the secondary. It's hard to tell what the intent here is.

Larry, Is there a basic dimension defining the angle of the two planes from one another?

[[Me...]]

Even if you considered D-B as a mathematically defined surface, point cloud, whatever, D still does nothing as a co-datum because it's already constrained as the primary. It's can't go anywhere. Check it as D-B-C and call it a day.

It's hard to tell if D and B are perpendicular to each other from the image. If they aren't then I would surmise they did the co-datum because they didn't realize/understand you can have a secondary datum that isn't perpendicular to the primary and thought they needed to use both of them.

[[An...]]

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They are not perpendicular.
The designer is pointing out the intersection line although it makes no difference
if you regard B or D-B.
See attached.

Contribution_24_05_2019.pdf

[[La...]]

I'm sorry I have not responded before now. I got very busy and didn't have time to look at the responses after my last post...Andreas is correct in that B and D are NOT perpendicular to each other. My thoughts were that the intersection between B and D would be the D-B call out, but from what I am hearing, B will be the secondary datum for this True Position.

D-B Print.pdf