Before milling an object you always need to adjust the coordinate system of your machine controller (e.g.
[Bad Link]). This operation is quite easy for the planar axes x and y. Only z is a bit tricky, since it usually needs to be quite acurate. Otherwise you risk to mill slightly too deep (damaging the base of the milling machine) or slightly to high (the cut through the object is not complete).
Touch off is the initial adjustment of the z axis by measuring the height of the lowest point of the milling tool. Read more »