Anneal the area around the original holes with a quick application of an acetylene torch flame, if necessary. The surface hardening will probably be worn away already. I'm about to try this on a set of junk shafts I was about to discard, so it's possible a carbide bit won't be needed to cut the shaft material. If a file will scratch it, a high speed steel bit or tap will cut it. Just thinking out loud on this one- - - -haven't tried it yet.
Jerry
