Strange question, but how do you make a curved fuselage frame, as fitted to an Avro Lancaster or whatever? I appreciate than huge presses were employed in mass production, but what if you only required one or two?

Large presses were less used than one might imagine….as all the responses illustrate forming sheet metal ‘frames’ was and is a hand skill (at most, semi-mechanised). Guillotining, folding, rolling, flange making byhammer or ‘flow-forming’ over exact patterns, curving with an ‘English Wheel’ did a lot of it.