Originally Posted by
grumpus
This is why we always start threads by hand - if you use a tool everything can feel fine until it isn't, the thread galls and you're left with a mess to clear up. It's a good idea to chase the bottom bracket after galling has occurred, because part of the cup thread may now be welded to the shell, making the cup hard to remove in future.
Conversely, part of the shell may also be welded to the cup. If you intend to reuse the cup, be sure to clean the threads thoroughly with a stiff wire brush and inspect for remaining debris. You may have to dig it out with a pick or even chase the cup threads with a thread file.