Hi Robin & Tony
Thank you for your interest with the handwheel gearing . That reminds me in the sixtys We had a job with internal gearing for the Navy a counting gismo We managed using a vertical slotter on a Debeigh Mill Old hat you may say but it may work in a home workshop.
Recently at work !!!!!!! 8 years ago we cut gears using a programed wire eroder.. That would be no good for a blind hole. Sorry drifting away from thread again
Regards Nobby