Making a stitching pony

I would have added dowels when gluing that seat board.

The foot mechanism is not shown, you'll have to figure it out, either a pedal where you need to maintain pressure or you could add a metal-tooth break so you can crank down the peddle and the tooth will keep it down. I would also add a spring in the inside for a better opening action. Or you could use a system with a lever-grip instead.