Make your collar a good fit. Bevel the hole for about 1/16th at 45 degrees
approximately. Braze with a silver alloy.
The advantage of silver soldering or silver brazing is that the joint
will be very strong, temperature distortion is minimal, and you will not
need to machine off excess if you are careful. With TIg you will be putting
too much heat into the shaft risking bending.
The shaft and collar clearance can be as much as .005 I would try for
around .003 plus to allow the silver alloy to suck in. Set the shaft
vertical with a pipe sleeve on the outside to support the collar in the
correct position. Apply flux paste to the shaft and collar hole before
assembling.

Randy

"Loren" wrote in message
oups.com...
If you were in my shoes.. what would you do?
A shaft is needed for a machine, 1.5" dia, but with a collar at the
middle of it. The collar needs to be about 3" od and about 1/2" thick.
Access to machining equipment is limited. No mill, and an abused lathe
that is too old with only basic basic tooling. Budget being the eternal
issue, I am planning on machining the collar out of mild steel and
carefully TIG welding it into the shaft, and then re turning it to cut
away excess weld and to make sure it's not crooked as hell. Has anyone
tried this and failed because the shaft warped excessively? suggestions
please...

I would attempt to machine the shaft from larger stock, except it would
be a first lesson on super close tolerances on the 1.5" as well as the
nice finish. overall length of shaft is perhaps 12".

Thanks for the advice
- Loren