RD - if i took a bit off the outside of the tap then i guess the cutting edge of the lands would be blunt - given the bolt thread is losing its outer edge, I wonder if a blunt tap would remedy the female thread's damage? and accurately starting the tap in the damaged thread could be tricky
Wouldn't be blunt privided the grinding was slightly angled, in the same way a drill is sharpened. Hell, we're only talking a couple of thousandths of an inch - maybe no more than a thou off each segment. Frankly, you won't notice the difference between that an an unmolested tap.
Whilst I usually defer to John's advice in light of his engineering experience, I have to diasgree with the silver steel idea. A fair bit of work involved, when the alternative would take perhaps a minute or less at the bench grinder. But, more importantly, silver steel tends to be brittle and I'd rather not contemplate leaving part of a hard home-made tap broken off at the bottom of a hole in the crank.
