Rolling between a flat surface and a board about 4" wide in your hand works fairly well. Remember and straightening will start to work harden the copper so best to anneal before you start to bend it.

Don't know about this size but there are small hand tools to do this by pulling through rollers. Sold by brake pipe suppliers but I may have seen them elsewhere – "Repair Shop" perhaps.

Are you annealing it with a fag lighter?🙂 Getting it straight, by rolling between flat surfaces, might have limits to length, but any decent gas torch should enable you to steadily progress from one end to the other.

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Hi Bo'sun, by using a pipe applied to the hot end, you introduce a barrier to heat conduction at the interface of the pipe to the hot end part. Every such barrier will seriously reduce heat transfer from a hot item to a cooler item. If you can fit a water jacket around the hot end and transfer heat directly from the hot end to the cooling media the heat transfer will be far better. This method is used in the majority of liquid cooled IC engines in the world, for good reason. Only mentioning it as food for thought, and may save some cost and time straightening copper pipe.

Devcon used to be the stuff, the one loaded with aluminium -powder. Soft solder would be better I think. However as others have said a proper water jacket would be a lot better. If you're pumping the water then arrange the flow to be tangential in at one end and tangential out at the other, then it sort of spirals round and you don't get any dead spots

Edited By duncan webster on 08/12/2020 21:35:15

Edited By duncan webster on 08/12/2020 21:35:52

Another way to straighten tube (or wire, etc) is to unwind as much as you can, fit one end in the vice, and pull the other. As you do this you will feel the metal 'give' as you get past the springiness. That should be enough – at the cost, of course, of 2cm at each end.

If you don't feel the 'give' it may be that the tensile strength is more than you can pull. Annealing will help – but this can be counter-productive if you need elasticity – eg when making a coil spring.

Oh, look, John Baron has just beaten me to it.

And you will improve conductivity between tube and cylinder with solder – soft or (even better) hard.

Cheers, Tim

Sorry re my brain fade / typo hot end vs cold end, of course OP did mention cold end was where he was working. I still think a water jacket where you want to transfer heat will be much more efficient than coils wound around. I agree with others who suggested soldering the coils or using heat transfer compounds would help if coil must be used, but a jacket and liquid or gaseous cooling media is a better method to move heat.