Originally Posted by
sloar
I have a nice set of Campy brake calipers, but the mounting bolt threads are screwed up. I need to buy a die to chase the threads. Does anyone know the correct thread size and pitch?
Couple problems:
- the bolt is chrome-plated, which kills cutting tools.
- (recycling some verbiage I wrote in a different thread) The problem is, how do you start a threading die on a screw with the first couple threads mangled? There's no way to start it in-phase with the good threads farther down, so the die will probably start cutting out of phase with the good threads, and ruin all the threads, even the previously-good ones. I'm not even talking about the problem of starting the die aligned with the axis of the part; that can be achieved on a lathe, or with some sort of custom-made pilot on the die holder (but you have to make the pilot, it's not a stock part anyone sells). But no amount of skill or technology will overcome this phasing problem; only blind luck will save you, maybe one out of a thousand tries.
Of course your threads might be only a little damaged, and the die
might start straight and in-phase; then you'd only have the chrome problem. If the die isn't too expensive, maybe worth a try.
But me, even though I have the die, I'd probably re-shape the bad threads with a triangle file, and magnifiers to see what I'm doing.
Optivisor FTW! Maybe if your eyes are younger than mine you can do it without magnification. I know a real Optivisor is kind of expensive, but there are generics that are much cheaper.
Pro tip: attach a small headlamp to the Optivisor, for bright light right where you're looking. Not the kind made for outdoor use like jogging at might, they have a narrow beam. For close-up work, you want a
flood or "floody" beam shape, else the little spot of light is never right where you're looking. I use a
Zebralight. Expensive, but they will change your life, so useful in the shop I use mine every day. (Again, knock-offs can be much cheaper, if you don't need Zebralight-level quality.) I have several, and one stays attached to the Optivisor with zip ties. If you get the type that takes a 18650 lithium battery (longest lasting), you'll also need a charger for 18650s, and probably at least two cells so you always have one charged.