It can be done, of course. Machining a bigger hole isn't hard (although not as easy as it sounds, because end mills have some runout, so you want to use a small mill and turn the crank on a rotating table to get the hole just right in size).
The problem are the threads. The flat-bottom tap you need to cut the new threads is not a standard item. Making one costs more than a crankarm. In fact, you really need 2 or 3, each less conical than the previous one, so you can start the threads, then enlarge them until they are the right size. That is how the threads in Rene Herse stems were done for the stem caps - I have seen the three taps for that.
As you can tell, it's not cost-effective, not even for a repair if your existing threads are completely stripped.
Jan Heine Editor Bicycle Quarterly 2116 Western Ave. Seattle WA 98121 http://www.vintagebicyclepress.com
At 8:19 PM -0700 6/28/10, donald gillies wrote:
>I have some un-mated stronglight 93 right arms (165 and 170mm), and
>I'd like to buy some generic left crank arms, but i'd still like to
>have a matching crank set. Is it difficult, or does anyone offer a
>service to increase the threading from 22mm to 23.15mm so that my 2
>crank arms can be matched, i can polish and maybe reshape the left
>arm, put stronglight caps into both arms, etc., and sort of have a
>pseudo-matching crank set ?? I'm just curious, thanks.
>
>- Don Gillies
>San Diego, CA, USA