In a recent study, atomic force microscope is used to cut the graphene. Cutting forces are also measured with higher single cutting force along armchair direction than zig-zag.
http://apl.aip.org/resource/1/applab/v101/i21/p213101_s1?track=APLDEC12
http://apl.aip.org/resource/1/applab/v101/i21/p213101_s1?track=APLDEC12