Originally Posted by
unworthy1
the best results I ever got was when a guy who used to post here (Frank B. in New York) cut extra threads on a CIOCC fork using his lathe and a thread tool, that turned out perfectly tho I was required to remove all the chrome plating before sending it (used emery cloth).
IMO this is the best way to cut them BUT Frank does not have the set up anymore and the only guy in my area who MIGHT have done the same (using a lathe), namely Bernie Mikkelsen, will not do it either.
It would be an enormous benefit if somebody with machining experience and a lathe would offer this service, the cost of a thread-cutting tool is far less than for a good quality die and in the hands of somebody who can use it the lathe does a much more reliable job with less wear and tear (again, IMO).
Agreed doing it on a lathe is Best Practice. It's more time consuming and requires a big expensive lathe, so it's bound to be more expensive than hand-threading with a die. Unless you get a bro-buddy deal, like provide a 6-pack to have a hobbyist friend do it. There are probably things that can go wrong, but they always came out top notch for me, the half-dozen times I did it, so I consider it safer than the die method.
unworthy1 , when you say a threading tool, do you mean a die? I'm talking about doing it with a single-point tool. Though there are carbide inserts that actually have more than one thread-form cut into them, I'd still classify those as "single point", as opposed to a die.
Another method I've heard of, but never seen in use, is a three-piece expandable die that's used in a threading machine (can be a lathe or a dedicated threading machine). They cut threads just like a die but then they open up to let the part out, so there's no backing up. Tesch used to have one, and he threaded all his forks, so that he only had to make one size of fork in batches, cutting/threading them to length as needed for different frame sizes. He also claimed (conveniently?) that all race bikes should have the same rake, regardless of head tube angle, a dubious claim IMHO. He used a very short-offset rake and people loved the "track bike" style handling. He was so efficient at steerer threading, including turnaround time, that the shop I was at sent forks to him when they needed more threads. This was a shop that had a lathe and a full Campy toolkit including their excellent die with piloted holder. But after you've ruined one expensive fork with your 0.2 kilodollar Campy tool, you're twice shy. And our clapped-out pre-WWII lathe was not great for the job either. Other than round-trip shipping time, sending them to Tesch was painless. I only bring this up in case someone wants to research those expandable dies and see if there's somone in your city who has one.
My "new" (1982) Taiwanese lathe is still disassembled for cleaning and rejuvenation, but I expect it will make good threads once I get it running. I'm actually working on it today so I hope that'll be soon, then maybe I'll be able to offer steerrer threading service. I also have a Campy die/holder in good shape, but I'd be nervous using it on a customer's fork, for more than a few threads. I think single-point on the lathe will be my go-to method. I've also heard some people recommend single-point cutting the thread to 80 or 90% depth and finishing with a die. A sharp and clean die can easily cut that little bit extra, I think probably very safely (touch wood!), so I might try it. Measuring the thread depth with the fork still in the lathe is tricky, involving a micrometer and three thin wires placed in the threads, and you can't take it out to try it with a headset and then put it back in the lathe if the threads aren't deep enough. Well you can put it back, but you lose precision. Anyway I've said too much, this level of detail is interesting to maybe one person out there (if I'm lucky), so it's time to sign off.
Mark B