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Tim Ostley	09/03/2010 13:58:01
17 forum posts 2 photos	Hi, I have a boiler kit with flanged plates and a flat boiler barrel which needs rolling and soldering. The silly question is what length the flat boiler barrel should be before rolling. The copper is 13 G so is thick enough that the internal circumference of the rolled barrel and the external will be different - which do I use or do I use the median? Since I have flanged plates, the resultant diameter needs to be reasonably accurate. Help! Tim
Weary	09/03/2010 19:20:34
421 forum posts 1 photos	What you are after is the 'neutral axis', also known as the 'K-factor '- but not like on Harry Hill's TV burp, of copper sheet. This is the ratio dictating the layer in any rolled thickness that neither compresses nor stretches, it will lie between 0.25 and 0.5. From memory : the 'inner' one third of thickness compresses, the 'outer' two thirds thickness stretches. So basically your circumference is calculated two thirds of the way into the thickness of the boiler plate, measuring form the outside. (A common rule of thumb is Circumference of boiler + 1.5 times thickness of plate = flat size to cut.) But.... you might prefer to be cautious and cut over-length then reduce the rolled sheet to fit as (and when) it is rolled up! Maybe worth googling 'neutral axis copper sheet' or 'K factor copper sheet'. ??? This has also been covered to some extent on this board here, having just glossed it I think it will answer your question OK. Phil
Tim Ostley	13/03/2010 16:01:47
17 forum posts 2 photos	Phil, Many thanks for the helpful post. At least I will know that if the rolled barrel is the wrong size it is due to my own incompetence!! Best Regards Tim

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