On Tue, 11 Sep 2007 08:58:24 -0700, wrote:

I have a BUNCH of shafts that need to be welded (using tig) on the end
to secure an arm that is swaged onto the shaft. The weld will be
about .375 long, bonding the arm to the shaft. Directly behind the
arm, with about .250 clearance is a nylon bushing.... I don't want to
melt the bushing when welding. I have to weld a bunch of these... in
the hundreds. MIG welding puts too much of a bubble there, and the
tig looks OH soooo much nicer.

I need an easy setup to weld this without putting heat into the nylon
bushing.

Nu-Calgon Thermo-Trap heat sink paste - available at welding and
refrigeration supply houses. Goes on like toothpaste, and sticks and
cools the item it's coating (like a refrigeration ball valve or
reversing valve) while you braze the valve in a half inch away.

http://ftp.nucalgon.com/ftp/prodlit/3-61.pdf (800K)

For a production line situation like this, couldn't you install the
nylon bushings AFTER the welding process? And if they come installed
in the part pull them out, do the work, then press them back in.

A bit more work to R&R but no material costs for the heat sink paste
compound (or whatever method you settle on), and zero chance of
melting the nylon because it's 5 feet away...

-- Bruce --