Had a bit of a problem last night, where the collet on the CNC router went on smoothly, but after a cutting job, it had jammed on solidly. I suspect the collet was slightly oversized (or heated up more than the threaded shaft) and slipped a thread, causing a cross-threaded situation.
In any case, what it meant that once I managed to get the collet off, the thread on the router shaft was shagged. Badly.
In hindsight, if I had known it was going to be that bad, I would have been better off grinding a gouge in the collet, and used a nut cracker to snap the collet in two to remove it. Hindsight is so 20:20
In any case, I now had a threaded shaft that nothing could be screwed onto. I went shopping around for a die (as in a tap & die), but finding one that was 25mm proved a bit tricky. Tried Total Tools, but not only did they not have anything close to the size I needed, but the guy serving me didn’t even know how to use a digital caliper. How can you work in a tool shop, and not be able to use such a fundamental tool?
I ended up having a chat with one of the fitters in the mechanical workshop at work, and while they didn’t have an odd shaped die, they were able to lend me a thread file, and some lapping paste.
The thread file worked a treat, getting the thread to the point that I could get a collet threaded on. Still bloody tight. But what really fixed things up was the second stage, adding some lapping paste to the threads, and running the collet on and off the shaft. And it worked. After an hour or so of threading it on and off, cleaning, filing, I had the thread back to being about as smooth as it was, if not better.
The thread has been damaged a bit from the experience, but at least I have been able to recover it enough to be operational again.