Can anyone tell me the best way to cut aluminium core? We use water jet to cut core and CNC machine to mill it. But i was looking for a manual method. I have tried desouter (diamond) cutter but it simply melts down the metal. I have also tried bandsaw cutter which gives a good finish but very difficult to control the tolerances.

Any Brighter Ideas??

Sharp knife between cells is the manual way to do it. 

As you are finding, it can be hard to keep tolerances or avoid damaging the material when using heavier equipment.  It is a bit easier to cut once part of a laminated cored panel.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant