Originally Posted by
Andrew R Stewart
Cutting new threads on a 4130 steerer (or other steel for that mater) can be more of a deal then most will ever know. The vast majority of threading dies provided by the bike industry are not really meant for cutting fresh threads but to chase/clean existing ones. It's a well known issue that tearing off the thread form when "cutting" is very easy to do.)
You speak the truth, as usual.
I have more success extending the threads if I don't rush the job.
Thin wall material will heat very rapidly during any process of forming or cutting, and even when liberally oiled, that heat can cause the tube to expand and the die to cut deeper than it should, making for a very rough job, and it's murder on the tool.
It could take me all day to extend the threads 20 mm, but I do it in very small increments letting everything cool completely in between.
It does not mean my time is not productive. I will have it all set up in my fork vise while I am working on other tasks, advancing the die maybe one complete rotation whenever I walk by it.1/4 turn advance, half a turn back to clear the chips.
This results in nice clean threads, and preserves the die.