For you metallurgists-ti galling

[oldpotatoe]

Ok, here's the problem.

Legend Ti frame, Record RD with ti fixing bolt. Regular customer, I have taken his RD off and put back on many times...no problem.

He travels with bike, takes RD off..this time when putting it back on..LOTS of resistance(it's not cross threaded, lathered with antisieze)..and when he tried to take it back off..no-can-do.

Brings it to me and to take it off, the typical mucho noise, WACK, Wack, big noise as it comes of in spurts, complete with sparks..obviously galled in there. So I DO finally get it off, swap the ti bolt with another one..re lather with antisieze..put it back on, not a lot of resistance but some..same issue getting it off again...

What is going on? Undoubtedly it's ti to ti galling but why? And what to do?

I'm stumped, never seen this before.

[TPetsch]

Well, you installed a new bolt, so you know the threads on that are perfect.

How about chasing the threads on the frame to clean it of any debris?

[gemship]

Originally Posted by TPetsch

Well, you installed a new bolt, so you know the threads on that are perfect.

How about chasing the threads on the frame to clean it of any debris?

beat me to it...I would suggest a cut type tap with some tap oil if they are thru threads otherwise a roll form tap although the cut type will work either way.

[zap]

What happens when you use a steel or al bolt.

[jpw]

is there an alu bolt available to try? softer metal. might show the issue in markings after it comes back out.

[SPOKE]

Carefully run your derailleur hanger tap thru the threads. I bet there is a little buildup in the root of he threads. Be sure to use cutting oil with the tap.
There is a posibality that threads in the hanger have been "pulled" a little by tightening the derailleur bolt a bit too much so now the pitch diameter of the threads are not quite to spec.

[David Kirk]

Originally Posted by SPOKE

Carefully run your derailleur hanger tap thru the threads. I bet there is a little buildup in the root of he threads. Be sure to use cutting oil with the tap.
There is a posibality that threads in the hanger have been "pulled" a little by tightening the derailleur bolt a bit too much so now the pitch diameter of the threads are not quite to spec.

What the Spokemon said.

Dave

[cmbicycles]

The threads were perfect on the new bolt, not likely perfect anymore. Sounds like the threads in the frame need to be tapped. When galling occurs the two surfaces pick up/transfer material from one surface to the other. The once smooth surface in the frame is no longer smooth, it likely has some ridges or bumps on the surface from picking up material from the old bolt. Sometimes with the galling they create a sort of anti-reverse burr, like parking lot spikes so you don't back up, it ramps up in one direction so it goes in smooth but is a bugger to get out.

I doubt it is so bad that it needs a heli-coil or similar, so tapping is the best bet. Being ti, I am sure you are aware, it is prone to wrecking taps so lots of good cutting fluid suitable for ti. After tapping so the tap goes in and out easily, try threading in the derailleur alignment tool, as I believe they have a hardened bolt.

You can try Teflon tape along with the copper anti seize when reassembling. In theory the copper particles in the anti seize are supposed to fill the gaps so the metal doesn't gall, the addition of the teflon couldn't hurt. Other industries use silver coatings on bolts prone to galling, or there are nitride coatings and anodizing options, but likely not economical.

[brenick]

For what it's worth, Lennard Zinn recommends never using ti bolts with ti parts. Mountain Bike Performance Handbook.

[Brian Smith]

Having made and been party to the making of oodles of these dropouts...I recommend:
45 degree countersink to the outside surface for about 0.020"
Fresh M10x1 tap running from the inside to the outside, and a good one.
Be sure to apply abusive sideways force to the tap once it has protruded through the thickness of the hanger.
Ti is somewhat tough to tap, and it's only in the later years that the operators creating the dropouts cared enough to make the threads work, and sometimes the taps supplied to secondary QC operators are equally secondary in quality.
This isn't the first time, won't be the last, but the fix is fairly simple.
Drilling a 9mm tap hole with a 9mm drill in titanium isn't as assured a procedure as one might imagine.
The 9.1mm drill was prohibitively expensive. So was interpolating the hole with a 0.25" end mill, though the result was sweet.
The later frames did a better job of this, I promise. Better tight than loose.

[AgilisMerlin]

this just reminded me to re-copper paste my ride.

[oldpotatoe]

Originally Posted by gemship

beat me to it...I would suggest a cut type tap with some tap oil if they are thru threads otherwise a roll form tap although the cut type will work either way.

Thought of that, try tomorrow but I'm worried I'll get the tape stuck in the der hanger or it will break off.

Also gonna try a steel bolt also.

Thanks for all the posts...

[Mikej]

Originally Posted by oldpotatoe

Thought of that, try tomorrow but I'm worried I'll get the tape stuck in the der hanger or it will break off.

Also gonna try a steel bolt also.

Thanks for all the posts...

Tap will cut its way out. Let us know how it works. I had this happen to an older moots clamp post - it's now a $200 bottle opener. The threads were really creaking in and out. Threads rolled. Re tap and be sure to clean it out and inspect for cracking at the thread root. It's not the bolt. Be sure it's not an npt tap.

[gemship]

Originally Posted by oldpotatoe

Thought of that, try tomorrow but I'm worried I'll get the tape stuck in the der hanger or it will break off.

Also gonna try a steel bolt also.

Thanks for all the posts...

No worries, when you feel the tap doesn't want to go further just back off and clean it with a rag certainly no forcing it. (I always used compressed air and blow it off, my days in the machine shop) eventually you'll chase the galling out. Good luck and keep us posted!

[51mondays]

Originally Posted by gemship

No worries, when you feel the tap doesn't want to go further just back off and clean it with a rag certainly no forcing it. (I always used compressed air and blow it off, my days in the machine shop) eventually you'll chase the galling out. Good luck and keep us posted!

well said

i use an aluminium bolt - i figure if the bolt gets screwed (excuse the pun) at least its disposable...