My guess is that the welding distorts the tubing, which causes the shaft
to get stuck. Even if the opening stays round, the welded metal shrinks
when it gets cold, so that could use up all the clearance. If you had a
smaller diameter shaft with more "Play" you might be able to avoid the
problem. Even 0.010 inch more clearance might be enough to enable you
to remove the shaft after welding. I would probably try for 0.020 inch
clearance before welding, but I am not sure that is enough.

If you cannot live with that much clearance you might want to use the
shaft to get the initial alignment, then clamp the tubing externally and
remove the shaft after welding.

Yet another approach would be to make an alignment bushing or whatever
that you would plan to leave in place after the weld, so it would not
matter if you could not extract it. If absolute accuracy was needed,
this could be the way to go. Perhaps the bushing could be internally
threaded, so you could position the bushing with a threaded rod (Only
engaged a couple of turns) and then unscrew the threaded rod.

Whatever, you will need to experiment until you figure out what will
work, before you start trying to build the final product.

Richard


Max Krippler wrote:
Hi,
Is there some compound or liquid that I can spray or rub on between
parts that will keep them from fusing from the heat of nearby welding?

I'm welding three pieces of tubing to a structure, and they have to
line up precisely, so I've got to have a shaft holding them in place.
The problem is that the heat causes the shaft to get stuck. I don't
think that I'm welding through the side (I'm quicker than that) but
something is fusing it in place. Any help for this?

Thanks, --Max


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