You are getting some good advice from previous posts. But FWIW, I use 80 grit and 2k grit for saddles. I also use a disc sander. There are more details on my routine here:
http://fingerlakesguitarrepair.com/p...e-proletariat/
I remove most nuts by first tapping it with a block of wood and mallet with the block laying on the frets. Then I tap it from the side with a punch. At that point it usually lifts straight up with some end nippers or I just push it out the side of the neck with more light taps from the punch and mallet. You can see the rest of the story here:
http://fingerlakesguitarrepair.com/g...ustom-new-nut/
With guitars that have the nut "inlayed" into the fretboard like strats and teles, you risk damaging the fretboard if you attempt to tap the nut free with a block of wood. Better to just use a punch from the side.