Originally Posted by
jimmuller
Now I'm curious. If you threaded this to Italian would here be much metal left in the BB shell? I haven't measured the typical BB thickness but I'm betting the answer is no.
That is why it should be a chase of the threads, and not cutting in new threads, IIRC. A chase tap will just dress the threads, kind of a shaping up process and getting rid of the shavings and the knocked/gouged places. The shop, or individual, needs to use a dedicated chasing tap.
A skilled machinist can better explain the detail than I can, perhaps one of our resident machinist will step up.
Bill