Method of evaluating a machined surface of a workpiece, a controlling apparatus and a machine tool

A method comprising the steps of:

• obtaining a shape of machined surface of a workpiece and shapes of cusps formed in the machined surface by simulation calculation based on a given set of machining conditions of the workpiece;
• calculating luminance of reflecting light on the machined surface based on the obtained shape of the machined surface and the obtained shapes of the cusps;
• calculating a contrast based on the luminance of reflecting light;
• calculating a spatial frequency of the machined surface based on intervals between the cusps in the machined surface;
• determining a position of the machined surface in a contrast sensitivity function diagram having a contrast axis and a spatial frequency axis and presenting a contrast sensitivity curve that separates a first region of the diagram from a second region of the diagram;
• and
• not changing the machining conditions when the position of the machined surface in the diagram falls in the first region, and changing the machining conditions so as to reduce visibility of the cusps on the machined surface when the position of the machined surface in the diagram falls in the second region.