An embodiment of the invention is a method of cleaning a material stack 2that has a hard mask top layer 8. Individual asset values are developed and listed in tables so that individual asset values can be taken from the tables and grouped in any desired manner. A first actuator is configured to vary the first segment between its first and second shapes, and the first segment is in its first shape when the first actuator is inactive. At least two ribs arranged parallel to each other in a wire guiding out direction are provided on the wire guiding wall and the wire supporting wall. The angular separation of the fixed brush cages 36, 38 and the separate brush cages 40, 42 is determined during assembly so that the angle can be adjusted to suit the application of the motor.