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Old 10-09-11, 03:14 AM
  #5  
dabac
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Depending on your fabrication skills, riding style, and risk tolerance(!), there are a couple of options on how to extend a steerer tube. But for an old fork, none of them are rational choices.
But if you like the machining, and are OK with the risks and waste of time - go for it.
I'd advice against the internal threading though, unless you have some serious tool access. Anything but a fine thread would remove a scary amount of metal from that tube.
If I wanted to do it I'd probably make an extension piece that'd look like a quill stem with a stepped diameter. I'd use a thicker-than-average screw for the wedge, and run a thread inside that for a normal top cap.
Or if it's a steel steerer, I'd make an extender with an internal press-fit guide and then braze it in place.
Some really old forks had a pinch wrap arrangement holding the legs and the steerer to the crown. If that is the case you may be able to replace the whole steerer. Don't expect smooth sailing though. Steerer tubes are usually a bit wider at the bottom than along the rest of the length. Getting a good pinch and getting the crown race to seat properly may be a challenge.
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