Marine Propeller

Patternmakers were the rockstars of the woodworking world, back in the day, and still are pretty badass. 

What does he do?  He makes something out of wood (generally) to precise measurements.  Then that wooden bit is placed in a sand mold and removed.  Molten metal is poured in the void.  Bingo, a casting. Often a BIG casting.

In the old days they'd build up the pattern with dimensionally stable wood, typically mahogany.  Now they might use plastics or plywood for big bits:



How do you make half a cylinder with hand tools?   The inside part.  The negative.  Easy!  A core box plane.