I have a tool and cutter grinder. I resharpen and make custom cutters.
There's quite a learning curve to be good at tool grinding. I must say with
the advent of ebay super cheap endmills, I wouldn't bother unless you just
want to do it. (My son and I wonder who's stealing all those endmills from
the day job just to ebay)

There is a unit for grinding the end of an endmill in a surface grinder,
maybe $50. If you have a surface grinder, start by using this.

Here's a link on endmill regrinding:
http://www.hanita.com/hanita_protect...info_start.htm