in the 1960's, New Zealander Ray Breingan was working in a small shop at the back of dealer Syd Mullarney's premises in Leighton Buzzard, England, making one off frames and exhaust pipes. Ray bent all his exhaust pipes by using a steel ball that he had welded onto a rod, and with this inside the pipe at the place where the bend was to be made, he heated the pipe to red hot on the outside of the bend, and worked the pipe into shape using the ball inside to keep the tube from collapsing. Obviously the ball was a reasonable free fit inside the pipe, but never the less, the finished bends were superb, without any ripples or creases.
This method may be well known in some parts, but Ray was the only person I ever say bending pipes this way.
Ray Breingan is unfortunately now deceased, but he and his son Peter were very active in Classic racing in New Zealand. Machine? Norton Dommie TT Replica!