I went to the hardware store to find a metal axle. They had nothing so short to be used for a yo-yo but they did have a long one. Is there something I can use to cut it to the appropriate size?
A hack saw will work. You should buy a couple nuts that fit. Screw them on and tighten them against each other. Then use these to hold it in a vise while you cut them to protect the threads.
Or if you have access to a Dremel tool that is better.
Whatever you use, use a fine file or coarse stone to smooth the cut end.
Not sure where you are located, but if there is a Lowes or Home Depot they should have “set screws” they will be in the drawers in the hardware isle. HD had a better selection when I was there last week.
jhb8426 solution will work too, you can use the nuts you screwed on to clean the threads up a little on the cut end by using them kinda like a die if you have a die to clean them up even better.
I don’t know if you have access to a lathe, but you can use a cutoff tool. A hacksaw should do fine though.
I personally use a drill, some nuts and a metal cutting saw. Attach the axle on the drill, use the nuts as an indicator for how much to cut. Turn the drill on and hold the saw onto the axle, let the game begin.