Ti alloys seem to blunt frame facing tools pretty quickly.

How does this compare with toughened/hardened steel? eg like that used in hub gears.

I have this foolish idea that it would lighten a hub gear considerably if its parts were machined out of Ti instead of steel. (Yeah, I know it would be expensive. )

So the question is how would they wear in comparison? Assuming any heat treatment or such like was done.

hardened steel is WAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAY harder* than ti used on frames etc, I don't know if heat treatment would narrow this. I think fibre of some sort is used for light cogs in cars?

*OK OK this may not be that scientific.

That's pretty much what I was thinking.

The cogs in a hub gear get some pretty hard use so I doubt any fibre versions would suffice.

I suppose my question should have been -is there is a lighter metal that could be substituted for the steel in that usage?

yes, but its cost would prohibit its use

If a rohloff is £750 imagine an TI one.

You probably could get a Ti alloy that would do – or have just steel teeth on a TI or CF body

You could probably lighten one quite a bit even in steel by drilling / milling away all the metal not needed but again at what cost.

thepodge – Member
yes, but its cost would prohibit its use

This is for fun, therefore cost not a major objection.

I'm thinking S-A 3 speed. Not too complicated.

(I usually find a sprinkling of Drillium can achieve the same results as lighter metals)

I think your problem here is hardenability, steels can be hardened to give excellent wear resistance. From memory the alpha beta Ti alloys which are the strongest ones used in most aero applications, are not particularly hardenable compared to steels. So I think the wear issue will be the stumbler here. Another issue is that the elastic modulus of Ti is half of that of steel, so you will get deflection of the teeth, you can combat this by making the sections thicker, but then that makes it heavier so you are back at square one on the weight issue with a potential wear issue. I will have a deeper look at Ti alloys when I am back in the office, there might be some better hardenable ones. I'll bet someone somewhere has thought about/tried this..

Could be the facing tool is galling when you use it. Bits of the steel will cold weld to the Ti and pull away from the tool causing wear. It's no good for gears…

XXX – Member

Could be the facing tool is galling when you use it. Bits of the steel will cold weld to the Ti and pull away from the tool causing wear. It's no good for gears…

Sorry I meant to address that point, you are right machining titanium alloys is a pin because of galling, you have to sharpen the tools every 5 mins.. Must be the same thing happening with the facing tools.

I would imagine the galling issue will make it a pretty poor performer as a gear too.

the tools needed to make the ti teeth would wear super quick too. nobody would make them as the tooling costs would be mental. it would be stupid money if it ever happened.

Titanium is best machined cryogenically this reduces galling, but you cant run a gearbox at liquid nitrogen temps…

Ah well, I'll just have to try Drillium.