Numerical control apparatus

A numerical control apparatus for controlling a chopping operation of a tool having a chopping axis including upper and lower dead points, and used in a grinding machine, comprising:

• instruction value output means for generating and outputting predetermined instruction values in response to an external command;
• instruction value calculation means for receiving said predetermined instruction values from said instruction value output means and performing a necessary correcting calculation generating a lower instruction value indicating the lower dead point and an upper instruction value indicating the upper dead point of the chopping axis output by a program, and generating corrected instruction values by adding said predetermined instruction values to the upper and lower instruction values;
• and
• axis control means for receiving said corrected instruction values output from said instruction value calculation means and controlling said chopping axis based on the corrected instruction values.