It is a correct call out for Datum B?
Am I well define for the Datum B?
Please help thanks!
Placing a datum at two lines looks confusing. Datums are usually flat faces of the part or straight edges when possible. You can call a hole or round face feature a datum if you need to, I think that would be a better callout than saying here is the centerline of Datum B. Datums should point to single features, not multiple. You could say one of those features is Datum B and the other is Datum C.
Can you make a markup on picture?
So that I have a better understand what you mean.
Does it apply to you?
Here is what I would suggest. Be careful using this, your boss or customer may want this to look a different way. Check with whatever authority you answer to about it.
That example makes it seem like the datums are the hole axes. But actually I think the intent is for the boss axes to be the datums, and then the holes are toleranced in relation to the bosses. Maybe those datum symbols should be attached to the circle at the top of the bosses instead.
Check here, maybe you will find something usefull. Learn the Basics of GD&T - GD&T Basics. It's a weebsite with tips how to use GD&T.
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