Controller for controlling machine tool having cutting condition change function

A controller for controlling a machine tool to machine a workpiece according to a machining program, the controller comprising a processor configured to:

• set respective upper and lower limit values of a rotational speed, a feed rate, and a cutting load of a tool for machining,
• set a range and condition for a change of the rotational speed and/or the feed rate of the tool in the machining program,
• calculate the cutting load from a variation between the cutting condition of the machining program before the change and the cutting condition of the machining program after the change, and
• determine whether or not at least one of the changed rotational speed, changed feed rate and calculated cutting load is within ranges of the respective upper and lower limit values of the rotational speed, the feed rate, and the cutting load,
• wherein, in response to a determination that the changed rotational speed or changed feed rate of the tool and the calculated cutting load are within the ranges of the respective upper and lower limit values of the rotational speed, the feed rate, and the cutting load,
• the processor is further configured to control the machine tool to machine the workpiece with the tool, according to the machining program and the changed rotational speed or changed feed rate of the tool.