It's worth mentioning the risk though. Sometimes the die will make nice-looking threads all the way down, but then when retracting, it rips the threads out by the root.

I have seen this happen only a few times but it was not easily explained; for instance the chips were cleared out and there was plenty of oil. Hard to make generalizations from such a small sample size, but it seems to be more likely if you're adding a lot of threads, say more than a cm or two. Much safer when adding just a few.

Bottom line is, think hard before doing it on an especially valuable fork. The conservative thing to do is sell the too-long fork to a tall person, and go find yourself a shorter one.

Another mostly-unrelated point: don't cut threads into a chrome-plated steerer, that dulls the tool faster. Better to sand off the chrome. I use "emery cloth" strip, a.k.a. "shop roll" or "utility roll" (names you may find it sold under). Good stuff to have around for a home-handyman. Usually coarse is fine, say 60 or 80 grit, but I also keep 200 and 400 grit around 'cuz I'm fancy. Just make sure to get all abrasive dust off the steerer before oiling it up for thread cutting.

Oh yeah one more: Maybe you don't need more threads, if you'd consider a less-thread headset. Kinda like threadless only you do use the threads, just for the top nut. Use the upper headset race from a threadless headset (well you can use the lower race too but it doesnt matter), then add spacers as needed, and a threaded top nut. You need some way to lock the adjustment; I do that with two thin nuts jammed against each other. Here are a couple of examples, rather extreme in the amount of spacers (these were on indoor trainer bikes). But depending on your fork size, you might not need any spacers at all. These forks both have less than an inch of threads, more like 15-20 mm.




The second one above uses an FSA Orbit headset, which seems pretty great for not too much money. The first one uses a Chris King, great but $$$.

That thin jam nut with the notches for a C-spanner came on low- and medium-grade Japanese headsets in the '70s and '80s. Might be a little hard to find nowadays. But there are other ways, such as removing the top lip from a regular nut (aluminum best so it won't rust where you trimmed it). Here's one done that way:



There are also one-nut solutions that lock in place, such as the Gorilla Headlock, or the Growler Headlock from Wheels Manufacturing.

Advantages of this less-thread idea include safer/stronger, no chance of the quill stem expander tightening in the threaded portion. Steerers breaking in the threaded portion is not exactly a common problem, but the stakes are high — it can definitly cause a crash, and you won't see the crack growing until it's too late. Also it's conservative in the sense that you can still put the fork back on the larger frame it was made for.

Good luck, however you choose to do it. Keep us posted!

Mark B