At 5:21 PM +0000 1/16/10, Hilary Stone wrote:
>I have a Stronglight extractor thread tap and it is marked 2/3 sp
>that it what you haver there.
If you have a lathe, it's not a hard tap to make. Take an extractor that fits the cranks, then measure the threads on that. Machine a screw with that thread in steel, then cut some slots. After all, you are tapping aluminum, so the tap doesn't need to be super-hard.
I made such a tap for TA/Herse cranks, and had good luck using it so far.
If the threads are very mangled or the hole is deformed (bike falling onto the crank), you may need two taps - one conical to get the threads started, then a second, flat-bottom tap to make the final cut.
Jan Heine
Editor
Bicycle Quarterly
2116 Western Ave.
Seattle WA 98121
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