In this report, ultra precision cutting of hard and brittle crystal materials with fly cutting which is one of the interrupted cutting was newly proposed and tested. In this experiments, single crystal germanium was cut with proposed diamond fly cutting, to examine the influence of crystal orientation and the change of critical undeformed chip thickness in 0, -15, -30, -40 degrees of the tool rake angle. From the experimental results, critical undeformed chip thickness was largest in -30 degrees of the tool rake angle, and the undeformed chip thickness was 235nm which is about 4 times compared with the conventional turning.
