I needed a piece of bent tube ( or pipe ??) for a project I was working on , and after trying a couple of people locally who could only bend it using a hydraulic bench bender that had fixed radii for the size of tube that were too small for my purpose , I decided to do it myself . I used 35mm steel with 1.5mm wall.

     First I made a form out of a piece of wood , a half-circle cut to the inside radius of the final curve I wanted. I used wood a little thicker than the tube diameter so it stood proud . Then I cut another piece of thin ply slightly larger and screwed it on so there was a lip to the half-circle about 3/4 of an inch big. I then pushed fire cement into the space where the steel pipe would be bent so that it protected the wood and also made a profile for the pipe to fit in and would help stop it kinking when it was being bent.

        The form was mounted on a sheet of metal on a wooden pallet that fitted over a stone bench in the garden . It must be fixed solidly , you don't want any rocking about going on when you have a red-hot pice of metal in your hand . Any bits of the wood the hot metal might touch had metal over them to stop them catching fire . There was a piece of wood screwed well into the pallet to hold the pipe in place , and a small piece to push the end of the pipe against to hold it in the right place.

       I heated it in a channel made of storage heater bricks lined roughly with bits of ceramic fibre I had left over from building my kiln . I left holes for the burner and and for the hot gasses to escape from. I needed to be able to get to the end of the pipe to turn it so as to heat it evenly , and then to slip a wider pipe over to take it out of the heat and to give me extra torque and a cool handhold when I did the bending. Don't forget that the pipe you are heating will expand , so the wider pipe must be a few mm bigger when cold , not a tight fit.

                  

With more bricks added and the burner in place

        Here's the thing lit up.

         You have to have a pair of heatproof gloves and some eye protection or preferably a face-visor - it's easy to get blowback as you move the burner and there are streams of heat emerging invisibly from between the bricks. It's possible to turn the pipe with really good gloves , but don't try it with cheap or non-heatproof ones , and always keep them dry , a glove full of steam = agony. The burner needs to have enough oxygen to work properly , you need to push it in and pull it out to find where it burns best , too far in and it will be starved.

         I filled the pipe with sand I had dried in the oven for an hour at 200 degrees , I put the oven on full for the last quarter of an hour . Again , damp sand = steam , bad news. I blocked up the ends of the pipe with bits of ceramic fibre.


         Once the pipe was in the heat it was fairly quick to heat , turning regularly and moving the burner down to the second gap in the bricks. There were enough gaps to observe when the pipe was cherry red over all the length I wanted to bend. Then it was just a case of slipping the bigger pipe over the one in the heat and sliding it out and into the form. It bent really easily and this is the result.

          Not quite perfect , but usable. The problem was that the burner focused most heat on the pipe a few inches after the point I wanted it to start to curve , so that bit started bending first because it was hottest and therefore softest.

         Next time I would make sure I pulled the pipe out slightly so as to heat that first bit of the pipe just before I took it out of the heat to make sure it was hotter than the rest when I started to bend. I also remembered a description I'd read of bending with sand and heat where they said to have a firebrick or similar to hand to press the pipe against the form where it doesn't naturally take the shape you want. I'd forgotten that , and also wouldn't really have wanted another thing to think about  , everything was a bit nerve-wracking already! I thought I had to work really quickly , but because the pipe is filled with sand there's a big thermal mass there and although it quite quickly loses its cherry-red glow , in fact it still bends fairly easily when it has lost some of its heat.