Quote:
Originally Posted by GH85Carrera
Imagine trying to do that in the era before the internet.
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Funnily enough, as I was reading this thread yesterday, I was thinking back to that.
I started my working career at a well-renowned British racing engine company. I was fortunate enough to graduate from my apprenticeship in the drawing office.
One day, the boss came up to my desk and asked me if I could create a set of drawings for a cylinder head from a 1920's Amilcar. If I recall, it was for a friend of his high up in the executive corporate ownership somewhere.
He gave me an incomplete set of original prints. In French. I also had an original (probably damaged) cylinder head that we cut into sections so I could measure it, and accurately develop all the cross sections for the drawing. The whole set of drawings was done manually, with a pencil on a drawing board. I don't recall how long it took, mostly off hours, but eventually I gave him a finished set of drawings.
He then took them to our pattern maker, who made the tooling for the castings. All of this work was done by hand to produce wooden patterns - basically, a wooden 3D jigsaw puzzle of the head. The skill of these guys was amazing. Unlike 3D modelling in CAD, there are certain aspects of a line drawing where the pattern maker needs to 'blend' a corner where several radii meet. This was very difficult to define on a 2D drawing, so the pattern maker just worked by eye. Add to this the fact that everything they make needs to be scaled for shrinkage because the material goes in to the mold hot, then shrinks as it cools. What they really make is something like a 103% scale model.
From there, the pattern went to our foundry where they used it to make the individual cores, copes, and drags out of sand. These are then assembled in the flask (sandbox) to form a sand model of what is effectively all the air around the head. The air space remaining is the part which is then filled with molten metal to form the head casting.
Anyway, I don't know whether we ended up machining the heads in our shop, but part of my drawing task was to include features to make the machining possible by including pick-up and clamping references.
Needless to say, I think the guy ended up making a couple of dozen heads to keep himself and the Amilcar population running for some time.
I dread to think what that would actually have cost if it hadn't ben mostly done with favors!