I bought a full set of the Brownells Magnatip's as well as the extra thin set. Rather than grinding the bits I use a very, very fine file, this then does not affect the temper of the steel,and is significantly more controllable. I just mount the bits in a vice and file very slowly to fit the appropriate screws.
The bits are also cheap enough if you break one. I definitely wouldn't use a grinding wheel, as in inexperienced hands they destroy the temper and can burn the steel and yiou then end up having to harden the steel which is just more hastle. The bits are aleady hardened to the best degree by the manufacturer.
