Does anyone know if there are any problems (or special concerns or techniques) when drilling and tapping titanium?
The frame is a Marin mountain bike frame made of Sandvik tubing. It does not yet have rack braze-ons, and it is being set up for fully loaded touring. Braze-ons could be added, but it seems better just to drill and tap the dropouts (there is plenty of room for this; there is no hole or cut-out area).
Someone (who knew a little about working with titanium, but wasn't certain of this) said he thought there might be problems with crack propagation or stress risers. The area (where the rack bolt will be inserted into the titanium) will be stressed quite a bit from the heavy loads on the racks, combined with bumps and rough roads.
So I don't know....
Is this something for an expert, or can it just be drilled and tapped?
If I were you, I would not touch the frame or alter it in any way. Titanium is somewhat toxic and could have adverse affects if hot shavings touch you. That is if you can find a ceramic carbide Titanium super heat treated blah.. blah... blah bit to even drill it. I tried one time on a pair of Sidi Titanium shoe plate and got no where fast. Burned out my drill and melted my bit. Very strong stuff.
Instead go take a 35 mile ride around the neighborhood and contemplate the purchase of a Colnago President with full Campy Record. He He.
Drilling and tapping will do far less harm than welding something to it.
Tell you what, find a part on the frame you don't mind scratching, if you can dig your pocket knife or a file into it, you can drill and tap it. Worst that could happen is you will break off a drill bit or tap, the stuff is hard and requires great care.
The metal can be machined using the same equipment and via the same processes as stainless steel.
Pure titanium is quite ductile, but bike frames are full of alloys, test it first.
If you are not good at this, I suggest a Machinist, a good OLD mechanic who drills and taps a lot.
I am also a Gun Smith and have no fear of drilling or tapping unless it's stainless or titanium, that stuff is ruthless. It can be done, with the greatest care.
In fact Titanium has the benefits of stainless but without the weight.
As far as driling goes a good cobalt tipped or full cobalt bit will work with lots of cutting fluid (or WD-40 can be used as a good cutting fluid) As far as tapping goes get a few taps in the size you want tap the hole first with one then again with another as Ti is hard on taps and drill bits made for steel. There are special coatings they use for facing and BB taps for ti that makes them almost useless for aluminum or steel because they cut to fast in those materials. I have drilled in Ti a few times with no problem as long as you get a good bit. I drilled out some odesey Ti axle pegs from 3/8 to 14mm. Did 4 pegs with one bit and it was still cutting good. It was also a 30 dollar bit
'''96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '12 Surly Pacer, All are 3x8,9 or 10. It is hilly around here!
Consider drilling a clearance hole (5mm) and attach the rack with bolts and nuts instead of trying to thread the Ti dropout. Drilling a hole is a lot less demanding than tapping it. Just be sure the holes are positioned so the nut on the drive side clears the chain and smallest cog.
Note to Thinline: Why do you think Ti is toxic? It is extremely stable and is used to make artificial joints. Hot shavings are a hazard no matter what the material but there is nothing particularly dangerous about Ti.
Titanium products tend to work harden so if you are going to drill do it in one hit and to size, don't stuff around with pilot holes and don't back the tool off during the cut, same with tapping make sure it is sharp and keep going if you relieve the cut thats probably where it will stop.
Low speeds high feeds and plenty of coolant/lube.
The Sandvik alloys are generally easier to work than the pure stuff the only hiccup could be how close to a weld you are planning to work.