In a
cutting method of an oblique surface by a rotary tool, for analyzing in advance a stability limit
depth of cut with respect to a self-excited
cutting vibration in consideration of a pick feed amount and a work
oblique angle and reducing the number of steps necessary for preparation and correction of NC data, a tool
diameter, the number of
cutting teeth and
dynamic stiffness of the rotary tool, a
cutting force coefficient determined by a combination of the tool and work materials,
dynamic stiffness of the work, the pick feed amount, oblique angles between the tool and the work and the like are used as input values, an initial value of the stability limit
depth of cut is determined based on the input values, and calculation is performed based on the initial value. In this case, the initial value is compared with the calculated value, the initial value is corrected by a certain rule, and the calculation is repeated until both the initial value and the calculated value fall in a
constant error range to thereby calculate the stability limit
depth of cut during the
oblique cutting.