Numerical control unit and NC program creating unit

A numerical control unit for a machine tool, comprising:

• circuitry configured to
• store a variation that is an amount of change to be used to change an override value, the variation being set for each workpiece material and the override value being a value that changes a command value of a feed speed or a spindle speed in an NC control program, the NC program including an end code that prevents further change to the override value;
• set the override value based on the variation according to a material of a workpiece being machined;
• change the feed speed or the spindle speed based on the override value;
• repeatedly compare spindle power consumption during machining with prescribed spindle power serving as a preset target value at predetermined time intervals to determine if the override value should be changed,
• change the override value by the variation each time it is determined that the override value should be changed until the end code is detected;
• store information on whether changing of the override value is permitted or not for each tool;
• determine for each machining process in an existing NC program if the machining process is a process using a tool for which changing of the override value is permitted;
• automatically insert a start code at a start of the machining process and automatically insert the end code at an end of the machining process if it is determined that the machining process is the process using the tool for which changing of the override value is permitted, the start code being a code that allows the override value to be changed;
• and
• start changing the override value based on the start code.