Forgot to mention the attaching the OpenFlexure Delta stage gears to a NEMA17 round shaft. Basically I warmed up the stepper shaft with a mini blowtorch and pushed the gears on. I try-fitted the motor to the Delta Stage Adaptor, added a drop of ordinary superglue, and pushed the gear into the right position. It drags the glue into the join and holds well enough for now. Probably should render something with proper inset nuts and retaining screws.

Speaking of dodgy fixings, the Delta Stage is currently on a thick piece of MDF with the microscope to isolate it from the bench bending when I lean on it (yes, that causes micron-sized movement). The microscope has a decent base, but the Delta Stage feet are slick PLA so after knocking the first one onto the floor I put some double-sided sticky tape under them. Very Heath Robinson/Rube Goldberg, but seems to work quite well.