Numerical control apparatus for machine tool and numerical control method for machine tool

A numerical control apparatus for machine tool, comprising:

• an NC program storage portion for storing an NC program generated for machining a material into a desired shape;
• an electronic cam data transformation unit which transforms the NC program stored in the NC program storage portion into electronic cam data;
• a constant circumferential velocity control command detection unit which detects whether a command for executing constant circumferential velocity control to keep the velocity of cutting substantially constant during cutting is present or not in the NC program stored in the NC program storage portion;
• a reference axis pitch setting unit which sets the pitch for generating data;
• a main shaft rotational velocity calculation unit which calculates the rotational velocity of a main shaft on the basis of parameters corresponding to the position of a cutting edge of a tool on the assumption that the velocity of cutting is kept at a desired value when a constant circumferential velocity control command is detected by the constant circumferential velocity control command detection unit;
• an axial feed velocity calculation unit which calculates axial feed velocity on the basis of the rotational velocity of the main shaft calculated by the main shaft rotational velocity calculation unit;
• and
• an axial position data computing unit which calculates axial position on the basis of the axial feed velocity obtained by the axial feed velocity calculation unit at intervals of the pitch set by the reference axis pitch setting unit.