The pipe bending operations were carried out on the third floor of the factory, at the Maxey Road end of the building.
Although light tubing could be formed on hand operated tools held it a vice, larger diameter or thicker gauge tubing such as exhaust pipes and handlebars needed far more power.
These bending machines used various diameter formed rollers which were grooved to the outside diameter of the tube to be bent, the root diameter of the groove being twice the inside radius of the bend required and the depth of the groove being approximately half the diameter of the tube.
This roller would be located at the centre of the machine while a similarly grooved roller would be located on the outside of the straight tube and the operator would use the machine's hydraulic power to rotate the outer roller around the centre until the required angle of bend was achieved.
Stops would be pre-set on the machine to ensure accurate repetition of the bends.
Compound angles on subsequent bends were achieved by holding the pre-formed part of the tube in a jig while secondary operations were performed.
The vast majority of pipe bending work was performed without any internal support (flexible mandrels, springs, etc.).
However, when extra tight bend radii were required, as in some of the racing exhaust pipes, it was the practice to plug up one end of the pipe and pour hot bitumen (tar) into the bore. After it had cooled to a more solid consistency, the pipe would be bent to its required shape and then re-heated to allow the bitumen to be extracted again.
This method prevented 'wrinkling' around the inner radius of the bend which not only would be unsightly but would have adversely affected the gas flow through the pipe.
[In the interests of avoiding any questions as to why this page is headed 'Pipe Bending' and not 'Tube Bending', the following
explanation/excuse is offered:
Technically, pipes and tubes are both long, hollow cylindrical items but, over the centuries, it has become the practice to
use the former term for items that are used to convey fluids (liquids or gases) and the latter for structural, supporting, items.
Unfortunately, in the field of motorcycle engineering, both forms are used in the manufacture of the final product. So, if a choice has to be made about the name of the department responsible for the manipulation work (by other means than the toss of a coin) then, as exhaust pipes are of larger diameter, and usually longer, than handlebar tubes , 'Pipe Bending' wins.]
|Tony Waldron||Prev. in Welding|