I can recall where the Americans had to convert Merlin blueprints to decimal fractions.
Despite both countries using the inch measurement system, the Americans had long ago changed to decimal fractions for ease and simplicity in engineering work - whereas the British still stuck with fractions.
So a Merlin blueprint would state [1 1/16"] whereas the Americans needed it to state 1.0625".
As far as the machining of early turbines for superchargers went, many lathes and hobbing and milling machines were set up with additional jig-holding drives, that moved the component as it was machined, thus enabling complex curves to be machined.
Gear cutters and hobbers are the classic machines for producing involute curves on gear teeth. Once you see a machinist who has gear-cutting skills in action, you'll see real skills with machine tools and calculations.
Wikipedia - Gear Hobbing