O/T - Bending 1/16" stainless tubing?

Terry Keeley · Feb 3, 2021

Want to put a 90* bend into this 1/16" thermocouple (316 ss sheath), looking for the smallest radius possible.

Any suggestions?

dian · Feb 4, 2021

vice and hammer.

Limy Sami · Feb 4, 2021

What's inside the thermocouple? ........... cos IM ''dated'' E TCs did not like being bent and pulled about.

Terry Keeley · Feb 4, 2021

Limy Sami said:
What's inside the thermocouple? ........... cos IM ''dated'' E TCs did not like being bent and pulled about.

Coupla small wires, they bend them at the factory but wanted to leave the end too long for my needs. Say the min radius is 1/2" but I think it could be smaller.

I'm looking at something like this, might make a roller for 1/16":

AARONT · Feb 4, 2021

Do you have any small tightly wound springs that just slip over the tube? It works for brake lines...

crossthread · Feb 4, 2021

Do you have to have the sheath? The only reason why I'm asking is that I have made quite a few thermocouples for measuring things like the temperature of one of my kilns etc. They are generally just two wires twisted together with two dissimilar metals (iron and Constantan for instance). The probe wires are usually covered with something like asbestos (or at least used to be). If you cut the SS probe off, skin the insulation back and twist the bare ends of the wire together you will still have a thermocouple probe that you can easily bend into any shape you want. You can check the calibration by using the point of transition between a liquid and solid of certain low melting metals ( I use lead). Hope this helps although you may for some reason want to retain the SS sheath. There is no reason as far as the functionality to do so however. Since the wires in the probe are already shorted together, I think you would be safe to use the technique Dian suggested,vice and hammer.

jim rozen · Feb 4, 2021

Thermocouples typically have a welded joint where the two wires join. Can be tigged, or there was a neat widget here with a carbon button in the center, tied to one end of a line plug. The other end went to an alligator clip. TC wires were twisted together, cut off short at the twist, and then snapped on the carbon button to generate a tiny weld bead.

Terry Keeley · Feb 4, 2021

Thanks guys, I didn't know about the spring trick, I'll look for one.

I need to keep the sheath (ordered it that way), it's actually open on the end with the twisted wires inside, a good compromise between durability and response time. It's going in a tuned exhaust pipe to about 1200F.

Mike1974 · Feb 4, 2021

Terry Keeley said:
Thanks guys, I didn't know about the spring trick, I'll look for one.

I need to keep the sheath (ordered it that way), it's actually open on the end with the twisted wires inside, a good compromise between durability and response time. It's going in a tuned exhaust pipe to about 1200F.

Too big, but thee are what they look like if you buy them.

https://www.mscdirect.com/product/details/32993164

boslab · Feb 4, 2021

Rigid small tube bender, shame I’m so far away I have one I used for that job
Neat little thing, don’t go too tight on the bend, they pack up if you do
Mark

BillE · Feb 4, 2021

Terry Keeley said:
Coupla small wires, they bend them at the factory but wanted to leave the end too long for my needs. Say the min radius is 1/2" but I think it could be smaller.

Are you sure? The 1/4 and 1/8" ones I've used have some sort of internal mineral(?) insulation, 90 degrees strikes me as tempting fate.

Gordon Heaton · Feb 4, 2021

BillE said:
Are you sure? The 1/4 and 1/8" ones I've used have some sort of internal mineral(?) insulation, 90 degrees strikes me as tempting fate.

I agree, Bill. With no separation it seems to me the ss shroud would pretty much negate the effect of the twisted area, especially if it is mashed firmly! At the very least, wouldn't it have the effect of shortening the twist to the crimp point? Just guessing, as I have no significant experience with these things.

David_M · Feb 4, 2021

This is the closest spring I could find. It could be used with that neat bender you found.

Extension Spring, with Loop Ends, 11" Long, 0.125" OD, 0.025" Wire Diameter | McMaster-Carr

Or, you might try winding 1/32" solid-core solder around the lead (to use with that bender).

kustomizer · Feb 4, 2021

Could you put it in at a steep enough angle that you wouldn't have to bend it?

newtonsapple · Feb 4, 2021

So I have some 1/16th sheathed TC’s just like yours that need to bent. In fact I think they have been bent already, the machine they went into is running, just haven’t checked the how the tech did the tc’s. I got a set of these springs: https://www.amazon.com/TUBING-BENDR3-MAX-MfrPartNo-321/dp/B000BQMMDQ

Like you I couldn’t find a tubing bender for 1/16th tube without making my own roller. Next time I am the local manufacture that does small stainless tubing, I will ask what they do.

The 1/16th tc should bend easily. The tech doing the recent work didn’t mention any issues. I have bent a bunch of 1/8th ones with a tubing bender. I’ve had maybe 10% fail, but I would need to check if those were grounded (tc junction attached to the end of the stainless) or ungrounded (junction not attached to the tube). I could see the potential to rip a grounded junction apart.

Terry Keeley · Feb 4, 2021

I picked up that little bender, neat little gadget. Tried it on some 1/16" brass I had and it worked great, forgot to check the radius but it's probably about 1/4". I think I'm gonna just give it a shot tomorrow.

Have the same thermocouple as this one that was bent at the factory, dunno why they said the "hot leg" has to be as long as this, I want to put mine in the header about 3" from the piston so only want about 3/8" inside the pipe.

It's for my mini dyno project...

newtonsapple · Feb 5, 2021

Terry Keeley said:
Have the same thermocouple as this one that was bent at the factory, dunno why they said the "hot leg" has to be as long as this, I want to put mine in the header about 3" from the piston so only want about 3/8" inside the pipe

So the insertion depth needed for accurate measurements is determined by how much parasitic heat sinking you can tolerate from the probe. This is the first article I saw that explains the issue;
http://download.flukecal.com/pub/literature/4137185A_w.pdf

Now if you are not as concerned about being accurate as you are about relative
measurements, 6x insertion depth is acceptable.

Another option if you need short insertion depth with high accuracy would be to use an exposed junction probe. I’ve built my own using wire as small as .001” for very fast response times. Those used polyimide tube for insulation, which may or may not work at your temps. The insulated wires were slid through a stainless tube so they were exposed and the end of the tube was carefully sealed with epoxy.

I would check out what options Omega has, but their current website may be one of the worst ever created with regard to finding what you want.

Terry Keeley · Feb 5, 2021

newtonsapple said:
So the insertion depth needed for accurate measurements is determined by how much parasitic heat sinking you can tolerate from the probe. This is the first article I saw that explains the issue;
http://download.flukecal.com/pub/literature/4137185A_w.pdf

Now if you are not as concerned about being accurate as you are about relative
measurements, 6x insertion depth is acceptable.

Another option if you need short insertion depth with high accuracy would be to use an exposed junction probe. I’ve built my own using wire as small as .001” for very fast response times. Those used polyimide tube for insulation, which may or may not work at your temps. The insulated wires were slid through a stainless tube so they were exposed and the end of the tube was carefully sealed with epoxy.

I would check out what options Omega has, but their current website may be one of the worst ever created with regard to finding what you want.

Thanks for the info, can't get your link to work tho.

These are "shielded junction" from Pyromation https://www.pyromation.com/Catalog/gen12.pdf, the rep said they act the same as exposed junctions but are more durable. Shud have a 0.01 sec. response time.

Terry Keeley · Feb 5, 2021

Made a new wheel for the bender and it worked great.

Thanks for the suggestions.

ps: that's not a kink, it's marker...

dian · Feb 6, 2021

about 30 years ago i wanted to measure the exhaust temp. on a car. i threaded some fitting into the pipe and sealed the k-probe wires with exhaust putty. its still there today and works well. even the teflon insulation survived comming out of the fitting.

O/T - Bending 1/16" stainless tubing?

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