The arbors I have out of music wire have a 3mm diameter. They do not seem to fit into the 623RS bearings that well. Maybe I could get them in by hammering them in, but they are probably a fraction of a millimetre too big. Should I be:
Filing their ends to fit?
Forcing them in? (I am quite concerned this would damage the bearings).
It's hard to tell from the videos what's happening.
Step 1 is the only usable option, but you already know that. :)
The first step would be to chamfer the ends. Cutting them to length often leaves a small burr on the end that needs to be removed. I twist them by hand against a fine grit grinding wheel. It is also OK to put them in a drill and touch a file to the corners.
If they still don't fit, they can be reduced in diameter by running them in a drill with sandpaper or a file. Fine grit wet/dry sandpaper with water usually works well. The bearings only need to fit in a small distance, so you only need to work on the ends.
Steve