LMB datum shift on an exterior diameter 1

[sendithard]

I'm trying to understand this callout that I think is illegal b/c I always default to physical hard gages.

So this primary datum is the exterior neck diameter of a screw. And the thru hole on the part is the position tolerance callout that uses LMB on datum B.

If you use LMB on an exterior diameter you in essence are saying go grab me the smallest collet that you can at this parts smallest diameter. Therefore, the part could never bounce around inside the collect.

It seems the virtual condition of this diameter datum B is the smallest it could ever be made at, so how can you physically make a gage for this and let the part move around at the same time?

 

[sendithard]

I wanna take you both out for a dinner, and watch the conversation Appreciate the help guys.

 

[3DDave]

You're welcome.

 

[Burunduk]

You were the one who suggested substituting RMB for LMB.

Yes, this is a legitimate possibility if the manufacturer prefers simpler inspection over a larger variation range.
I now understand your question better (I read it as "substitute with" instead of: "substitute for" the first time), but I am not concerned about the rejection of usable parts, from the reasons mentioned. If LMB inspection is to be insisted on, some inspection equipment that could otherwise do the job is not usable.

The earlier contention was that CMMs cannot handle datum shift.

Some of them can't, others can.