I just busted an E Eudoxa string while putting it on. That may have happened because the nut grooves are too narrow. I'd like to get the grooves widened, however if later I want to go back to using thinner strings will there be a problem? Will I have to get a new nut put on? Also, how can I know if the cause of the breakage is due the nut groove narrowness? How much of the string should be down in the groove and how much outside of it?