Hi DeadTom
I have to admit I considered the matter of the chuck. Going from experience (and my day to day drill is the same model as I got these motors from), Ive never had an occassion when the chuck slipped on a drill bit if the bit got stuck in something and its happened a few times to me. Often Id lose control of the drill rather than the bit slipping in the chuck. The shaft of the right angle boxes has a fairly substantial flat ground on one side which may or may not increase purchase even more.
If I do ever see it slip in the chuck, I may just file down the shaft to a hexagon or whatever to increase the grip.
My bigger worry is the right angle boxes. While the shafts and the bevel gear and bearings are steel and brass, the box itself is made of some kind of glass reinforced polymer. I could see that getting badly torn up so I intend to get a couple of sheets of brass and fashion a "cladding" for the boxes to hopefully beef them up a bit.
The LOvejoy couplings are very nice indeed.... Im a little unsure though how I would get them onto the drill motors (they dont end in a shaft when the chuck is off but rather some klind of left hand threaded "stump"). Machining the motors is off the menu (as I dont have any machines) and Im trying to keep to doing things "by hand" so to speak!
p