[Astroman (Andrew Wall)]

Hi all,

I am in the process of getting some equipment ready to automate my focusing. I have a Moonlite focuser installed on my 8" f4 newtonian and it has a shaft diameter of 4.8mm. I will be attaching a NEMA17/27:1 Stepper motor to it for fine focusing adjustment, the Stepper has a shaft diameter of 6mm. I cannot seem to locate a shaft coupling suitable. I can find 5mm to 5mm or 5mm to 6mm, I may be looking in the wrong places. Would I have to drill out the hole to make it suitable or is there another option out there? I have attached images of the Shafts and dimensions.

Originally I had the idea of using a 2:1 toothed pulley and belt arrangement, but directly coupling the Stepper to the Focuser looked like a better option. I would have gone with the Moonlite stepper motor, but new cost on these is a little higher than the price I want to pay, not too sure there would be that many around on the second hand market.

Help appreciated.