What do you use...

[dan]

to cut graphite thats 2.5mm thick?

[Crazy Canuck]

In small pieces, a dremel. For a large Sheet, maybe a jigsaw? Ive never done it.

[DirtRacinFool]

I use a Scroll Saw with light metal cutting blades, scroll saws work great because you can cut tight, clean turns and following lines is easy. I always use tape for a backing to help prevent splintering. Make sure you always wear a dust mask and eye protection. The dust from graphite can be very hazardous.