weldment callouts between two concentric cylinders

[blitz97]

All - not having utilized GD&T in a weldment capacity, I am interested in everyone's take on how to specify the GD&T tolerancing for two round bars that will be welded together end to end. I want their ODs to be within .015" of each other when an indicator is run along their respective ODs based on their coaxial centerlines.

Is this as simple as specifying one of the OD's as datum A and calling out a TIR on the other?

 

[jassco]

Hi, blitz97:

When you butt-join two rods, each rod is no longer straight. In addition, they won't be co-axial.

You just need a size to control overall OD, with each end rod controlled with its size with an "I" (independency).

Best regards,

Alex

 

[CheckerHater]

It doesn't really matter if your part is welded, glued, cast, or machined in one piece.

GD&T is simply a description of the requirements your part has to meet and it is based on function of the part.

Please look at the enclosed pictures. If it's important to control one diameter of the part in relation to other, the first picture is good enough.

If you actually want to establish a common axis of the entire part, and control both diameters in relation to it, then you will have something that looks like second picture. The round symbols represent "datum targets" - the areas of the part used for fixturing.

It is also possible that you want the surface of your part not to be obstructed by fixturing. In this case you may have to go the extra mile and establish temporary datum features like center holes. This also can be shown on your GD&T.

So, let me repeat one more time: only you know how the part works, so you make the final decision what is controlled in relation to what.