You're obviously right in so many ways, Mark.
I've done a good bit of welding, but I haven't ever done high speed
components that need subsequent machining. Once you pointed it out, the
difficulty was easy to recognize.
Elvis also rightly pointed out the possibility of not being able to
reverse the bit (which is a problem with my bit. Some bits for sashes,
btw, are made to be reversible for this very reason), but I still don't
understand why, if balance weren't an issue, the post wouldn't provide
sufficient alignment. I would tighten the nut, tack the bottom, then
remove the nut, cut down the post and braze it there. The alignment
should be fine because of the bottom tack, which holds it in the same
position as the nut did before, no?
I had considered heat distortion. I think brazing with a small enough
tip could avoid damaging the carbide, and I suspect the original
brazing would be just fine too, but it is a risk.
Gotta suck it up and shell out the $150....
That, or make the sash windows without mortise and tenon joinery, which
I really don't want to resort to.
Less wealthily yours,
ps: thanks again for good warnings