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I am making a model hot air balloon burner have a hard time bending the coil for it. Found this place hope someone can help. The coil is a square

Heres some examples
my problem is i bend my tube around a block of wood when i get done it wants to un coil into a mess
Make a wooden form the shape and size of the inside of the burner. Fill the tubing completely full of silica sand and tape the ends shut. The sand will keep the tubing from collapsing as you bend it around the form.

Ok, I just read in your other post that you are using thin wall stainless, so the sand thing may not work. You may need to invest in a tubing bender like this:

[Image: tubing-benders-tb04.jpg]

I would not recommend a thinner wall tubing because that will make it more difficult.

wall thickness is .020 tubing is 3/16 I tried a bender the coil is to small for it.

This is what i have been trying will the sand keep it from wanting to un coil after i finish?
No. For that you will need to over bend it a bit. Make your form less than 90º so when the tubing springs back it will be 90º.

Whats easier to bend the seamless tubing or welded? Should i stay with 316 or go with 304
304 should meet your needs.

Sand bending helps prevent the tube from crushing during bending. It works, but must be packed in very tightly. Another method is to fill the tube with soapy water and freeze it. I've never done this, but I hear from reputable sources that it works. Either method, the ends must be tightly capped. What I do is smash one end flat and weld it.

I might suggest trying a sand-casting mixture which includes bentonite clay, it will ram up quite firmly. I've never tried this, either, but it sounds like a good idea.

If you orient the seam on the neutral axis of the bend, it won't give you any problems.
What am i looking for to find the seam? What if i went seamless?
The seam will be a dark line running the length of the tube. There may be a slight bump on the inside of the tube at the seam.