Could it be this easy? Just add a knob to the hand wheel? I didn’t know, but the motor doesn’t work any more, so there was nothing to lose by trying. I drilled a hole in the hand wheel and attached a bit of dowel with a screw. Voila, a modern zigzag hand crank sewing machine, most useful for my small trailer where I don’t have room for a treadle base anyway.
(Even if I still had my treadle base, which I don’t.)
Turning the wheel around by hand is tiring, but easier than hand sewing, and slow, but faster than hand sewing.
It worked just dandy on my most recent trip to our cold new home, where at one point I needed to hem a piece of heavy canvas. Doing it with a machine surely did save my fingers.
“If it’s stupid but works, it isn’t stupid.”