Originally Posted by
scarlson
You may need a mighty good lathe and some tooling you don't really care about. Those BB axles are normally harder than a coffin nail!
I have a bunch of no-good axles and no-good cups and I have access to the lathes that could do it, and I still won't - readily available sealed BBs are going to be lighter, stronger, smoother, and more durable, plus you won't have to machine hardened steel.
It might not be that hard. I cut one in half with a hacksaw, not a particularly high-spec one, but it was hollow (picked that one so the sawing would be quicker).
And it might not be that difficult, I just took a 26.4 crown race to 27 on a mini-lathe with a carbide tool, it was hardened all the way through; no trouble.
But I agree, in most case off-the-shelf will be better in all those ways than what most hobbyists could do. If I had a crank for which axles were not readily available, like a Gnutti spline or the 3-degree SR, and an axle that was otherwise unusable, it'd be an option.