On Tue, 18 Jul 2017 19:19:38 +0800, Trumble
wrote:

I've never TIG welded - only amateur MIG & stick welding......


As part of an assembly process would the following be possible:


I've got a 304 stainless steel tube with some electronics embedded in
polyurethane inside it.

I want to put a 304 stainless cap on the end of the tube capable of
handling say 20 kg pulling force.

When fitted to the end of the tube the gap from the cap to the
polyurethane potting material will be 1/32"



How much heat would spot TIG'ing the cap onto the tube introduce to the
assembly?

Cool it with a damp cloth immediately after welding?



SPOT TIG HERE
|
\/
======================================|====\
| |==== \
| | |
POLYURETHANE POTTING | | O |
COMPOUND | | |
| |==== /
======================================|====/
^
|
SPOT TIG HERE

|---Tube 1/2" OD x 1/16 wall----------|-cap-|




Should I be looking at threading the cap into the end of the tube?
It looks like the cap fits into the tube from your ascii art. You
could drill a small conical hole through the tube in two places where
you want the welds. Use a 90 degree included angle spot drill. The
small diameter of the hole only needs to be about .030". Push the cap
in and TIG weld at the holes. It should only take a few seconds for
each weld. This would probably be safe. You could wrap a wet rag
around the tube before welding but I don't think that's needed. Just
make sure the person doing the welding knows what they are doing.
There is another option. If the cap could be as thick as .125" then
Loctite could work very well for you. Loctite 638 will bond stainless
steel quite well and will fill a gap up to .010" . If you have a cap
with a .125 wide contact area and .375 diameter it will take,
according to Henkel, 587 lbs to pull out. I use the stuff and it
certainly seems permanent to me.
Eric