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?

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?

Thread the cap. TIG is good for fine welding..but you will cook your
potting compound. You probably could do it with
tig...maybe..somewhat..perhaps..but it will take a really delicate
touch and a big shot of heat for just a half second or so. And you
will still likely cook the potting compound


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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?
Try gluing it, or using a "security screw" or a rivet. Or laser weld
it.

On Tuesday, July 18, 2017 at 7:19:51 AM UTC-4, Trumble wrote:

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"


I think silver brazing would cause much less heat to the polyurethane. But think it would still be too much heat.

Think about why you want the cap on the end of the tube. If it is to prevent liquid from reaching the electronics , you might find a O-ring seal would work well.

Dan

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

"Trumble" wrote in message
...
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?

1/2-20 is a readily available size for taps and dies. Here are the
other standard choices:
http://www.efunda.com/designstandard...=64&finish=147
1/2-32 leaves ~3/4 of your wall thickness intact.

I've been collecting 32 pitch taps and dies to cut and repair
electrical instrument threads. The F connector for video cables is
3/8-32, toggle switches are 15/32-32.

Not all lathes can cut 27 TPI but the others are easy. I cut threads
in thin-walled tubing part way on the lathe and finish with a die,
which starts straight and doesn't deform the work if it removes only a
little metal to reach final size.

-jsw

On 18-Jul-17 7:19 PM, 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?



Many thanks for the suggestions guys.

It looks like TIG might be iffy.

Threading the cap and tube would be ideal but is a lot of mucking around
for this job which I want to keep cheep.

I like the sound of the Loctite 638. I think I'll try it out.


There's always lots of invaluable advice here, thanks again.

On Wed, 19 Jul 2017 18:01:47 +0800, Trumble
wrote:

On 18-Jul-17 7:19 PM, 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?



Many thanks for the suggestions guys.

It looks like TIG might be iffy.

Threading the cap and tube would be ideal but is a lot of mucking around
for this job which I want to keep cheep.

I like the sound of the Loctite 638. I think I'll try it out.


There's always lots of invaluable advice here, thanks again.

Be sure to have 5-15 thousands clearance between the parts. A snug fit
will be NFG if it wipes off the glue when you assemble it.


---
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On 19-Jul-17 6:19 PM, Gunner Asch wrote:
On Wed, 19 Jul 2017 18:01:47 +0800, Trumble
wrote:

On 18-Jul-17 7:19 PM, 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?



Many thanks for the suggestions guys.

It looks like TIG might be iffy.

Threading the cap and tube would be ideal but is a lot of mucking around
for this job which I want to keep cheep.

I like the sound of the Loctite 638. I think I'll try it out.


There's always lots of invaluable advice here, thanks again.

Be sure to have 5-15 thousands clearance between the parts. A snug fit
will be NFG if it wipes off the glue when you assemble it.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Thanks - that's something I hadn't thought of.

On 19/07/17 11:55, Trumble wrote:
On 19-Jul-17 6:19 PM, Gunner Asch wrote:
On Wed, 19 Jul 2017 18:01:47 +0800, Trumble
wrote:

On 18-Jul-17 7:19 PM, 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?



Many thanks for the suggestions guys.

It looks like TIG might be iffy.

Threading the cap and tube would be ideal but is a lot of mucking
around
for this job which I want to keep cheep.

I like the sound of the Loctite 638. I think I'll try it out.


There's always lots of invaluable advice here, thanks again.

Be sure to have 5-15 thousands clearance between the parts. A snug fit
will be NFG if it wipes off the glue when you assemble it.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Thanks - that's something I hadn't thought of.

Best to check the data sheet for the the stuff you use as the
recommended gap varies and those just mentioned sound on the high side
to me.

On Wed, 19 Jul 2017 18:55:12 +0800, Trumble
wrote:

On 19-Jul-17 6:19 PM, Gunner Asch wrote:
On Wed, 19 Jul 2017 18:01:47 +0800, Trumble
wrote:

On 18-Jul-17 7:19 PM, 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?



Many thanks for the suggestions guys.

It looks like TIG might be iffy.

Threading the cap and tube would be ideal but is a lot of mucking around
for this job which I want to keep cheep.

I like the sound of the Loctite 638. I think I'll try it out.


There's always lots of invaluable advice here, thanks again.

Be sure to have 5-15 thousands clearance between the parts. A snug fit
will be NFG if it wipes off the glue when you assemble it.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Thanks - that's something I hadn't thought of.

Gunner is on the high end of that clearance. 638 will fill moderate
gaps -- and, as Gunner said, it needs some gap -- but it loses bulk
strength with clearances over 0.010 in. Keep it around 0.005 if you
can.

Otherwise, it's made specifically for cylindrical fits like your
project, and it's quite strong. Follow the instructions; it's an
anaerobic acrylic, and it's not entirely intuitive. It cures in the
*absence* of air. The bottle it comes in actually is porous to air,
which keeps it from curing in the bottle.

--
Ed Huntress

On Wed, 19 Jul 2017 12:16:22 +0100, David Billington
wrote:

On 19/07/17 11:55, Trumble wrote:
On 19-Jul-17 6:19 PM, Gunner Asch wrote:
On Wed, 19 Jul 2017 18:01:47 +0800, Trumble
wrote:

On 18-Jul-17 7:19 PM, 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?



Many thanks for the suggestions guys.

It looks like TIG might be iffy.

Threading the cap and tube would be ideal but is a lot of mucking
around
for this job which I want to keep cheep.

I like the sound of the Loctite 638. I think I'll try it out.


There's always lots of invaluable advice here, thanks again.

Be sure to have 5-15 thousands clearance between the parts. A snug fit
will be NFG if it wipes off the glue when you assemble it.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Thanks - that's something I hadn't thought of.

Best to check the data sheet for the the stuff you use as the
recommended gap varies and those just mentioned sound on the high side
to me.

Right you are.

--
Ed Huntress

On Wed, 19 Jul 2017 12:16:22 +0100, David Billington
wrote:

On 19/07/17 11:55, Trumble wrote:
On 19-Jul-17 6:19 PM, Gunner Asch wrote:
On Wed, 19 Jul 2017 18:01:47 +0800, Trumble
wrote:

On 18-Jul-17 7:19 PM, 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?



Many thanks for the suggestions guys.

It looks like TIG might be iffy.

Threading the cap and tube would be ideal but is a lot of mucking
around
for this job which I want to keep cheep.

I like the sound of the Loctite 638. I think I'll try it out.


There's always lots of invaluable advice here, thanks again.

Be sure to have 5-15 thousands clearance between the parts. A snug fit
will be NFG if it wipes off the glue when you assemble it.


---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Thanks - that's something I hadn't thought of.

Best to check the data sheet for the the stuff you use as the
recommended gap varies and those just mentioned sound on the high side
to me.

True indeed. I was basing it on epoxy..so its probably closer to .005