How fast can a bicycle headset bearing turn?

[ericc]

I was breaking up a junk 10 speed bicycle to get it out of the way. There are some parts that I am saving to repair another bike and some that I will melt (the alloy parts). As I was cutting up the frame so it would fit in the tiny garbage collection cans, a weird thought popped into my head. Could the headset be used as a light duty vertical milling spindle? A little bit of Internet searching suggested that bearing maximum speeds are mainly a function of ball material and lubricant, not size of races and not the fact that the bearing is open. The main limiting factor is temperature rise. There is a hole at the crotch of the fork through to the bore that looks large enough to press an MT2 sleeve in. My current expedient vertical head that is mounted on a horizontal mill overarm is a Harbor Freight trim rotozip type rotary tool mounted in a wood and sheet metal frame. It looks really silly, but it is rigid enough, and it does surprisingly accurate work. It would be nice to use larger end mills, though. I realize that the races are small, and the wall is pretty thin, but might this work? I didn't find anything with an Internet search, so either making a real spindle is too easy, or it just doesn't work.

 

[Inferno]

Headset bearings aren't built for anything like a mill would use. I'd put money on the bearings being toast in the first 10,000 revolutions.
The races on more expensive bikes might last longer but if you're cutting up a frame, it's more likely a cheap Huffy or Murray.

 

[piper184]

It would most likely depend a little on what type of bearing it is. The ones from my childhood were simple ball bearings in open cages. The races were cup shaped so you could put a little pre-load on them. They weren't sealed so they got a lot of dirt in them and wiped out fairly often, but not as bad as wheel bearings.
They probably failed most from the beating we gave them jumping the bikes and doing wheelies. With no suspension all the forces were transmitted to the lower bearing which was almost always the one to fail first.
If however newer and higher end bikes have better bearings, it might be a different story. Certainly the ones we had as kids wouldn't hold up to the abuse even an electric drill would deliver. I suspect the quality of the polish other dimensional accuracy isn't there for use as a spindle.
By all means try it if you wish, that is how we learn new things.
Let us know what you find out!

 

[mattthemuppet2]

You'd be money and time ahead to just make a spindle yourself. An old bicycle headstock and bearings would be worse than a drill press, which is a pretty poor imitation of a milling spindle

 

[Cadillac]

They explode apart in no time at all. You need a deep groove ball bearing to support the loads. You’d be better off with the crank rollers than the headset.