Win’s workshop shelves are packed with wooden patterns, from the tiniest fittings to the huge base for his Pennsylvania A5S tender. Pattern making is the starting point for building metal models and the success of the finished engine depends on its accuracy. Customwood is used in preference to wood as it is more stable.
“You can get sets of castings sent out from the UK but it’s a horrendous price,” says Win, who instead gets hold of the drawings and works it out from there. “It’s like making a huge 3D jigsaw,” he says. It’s not a simple matter of replicating the final form, as both shrinkage and the negative spaces have to be taken into account. “The metal shrinks when it solidifies so the casting ends up a bit smaller. The shrinkage is different for each type of metal so you’ve got to think it out and do the maths.” To make the moulds for casting, the Customwood patterns and cores are set in resin sand, with a gating system built in to channel the molten metal.
“It can be a bit of a braintwister, especially getting the negative and positive shapes in the patterns. It’s a painstaking process, especially making cylinders with complex coring. The pattern doesn’t look anything like the cylinder, as it has outside core prints on it,” says Win, who has built about 14 boilers in his time, the biggest for his Burrell traction engine. “I make all the moulds and cores and fit them together so [that] I don’t hold up the blokes at the foundry,” he says. Once they have been cast, the metal castings are machined and filed to fit. On the bright side, if it all goes wrong, at least you can turn them back to liquid again, he says.