Hi guys, first post - I did a search and could not find much on this. I work on equipment that requires removal of rusted in place 1/2-in flat head hex socket bolts or enlarging laser cut holes in steel and go though quite a few drill bits (HHS and cobalt). I am using a hand drill and use a Darex sharpener to re-sharpen the bits. I find after a number of times sharpened the bit doesn't cut as well or not at all. Either only the end of the bit was tempered or I overheated the bit and lost the temper? Would like to know if it is safe to re-temper the bits and best way to do it.