You can make them from a short piece of 1/2 inch copper tubing, an end cap, a small hose clamp and a 1/4 inch brass bolt or 1/4 inch bolt/nut. Take a short piece of copper pipe and cut two slits in the end to make it slotted. This end is slipped over the shaft and held secure with the small hose clamp. Drill a hole in the end cap and solder the brass bolt with the head inside the cap. If the bolt is not brass just use a nut and a jam nut to secure it. Solder the cap onto the short copper pipe and you know have a 1/4 inch to 1/2 inch adapter. It may look a little rough but if you are neat and it is not readily seen it is fine.
yucky. Id rater take a piece of 3/4" aluminum rod, bore a 1/2" hole on one end and either turn down the other end to 1/4" or at least bore a 1/4" hole in the other and use a couple setscrews with some rod.
I usually dont even bother. I buy a shaft coupler and drill one side out larger then the other side put a 1/4" rod in and I'm done.
Yeah I've seen a lot worse too, but its my build and and I didn't want to do any rigging like that. I had a reducer, but then decided I would hav e to mount it further back. Didn't want to do that either. So I spent the money and did it right.