Electronically controlled substrate working apparatus

A method of operating a substrate working apparatus in a three-dimensional space, comprising:

• configuring a tool to remove material from the substrate, in which a spindle motor is coupled to the tool;
• configuring a feed motor to cause relative movement between the tool and the substrate along a feed path in the three-dimensional space, wherein the feed path is specified in a part file, the part file storing data corresponding to each of a plurality of different spatial locations on the feed path from which respective sets of compliance values are determinable;
• configuring a controller to control the spindle motor and the feed motor, and a tool load measurement structure configured to provide a tool load value to the controller, the method comprising:
• determining a variation of the tool load value from each set of compliance values at each corresponding spatial location as the tool moves along the feed path;
• wherein the controller is further configured to cause the feed motor, the spindle motor or a combination thereof to perform a response action at each location along the feed path in the event that the load falls outside the corresponding set of compliance values for that location, wherein the performed response action is selected from a plurality of different response actions according to the determined load variation;
• wherein the controller is able to be provided with the part file, the part file containing an electronic representation of a part to be made by the apparatus from the substrate and containing information from which the controller is able to determine the feed path and the sets of compliance values corresponding to the different spatial locations along the feed path.