Thanks Ozz, that is looking very interesting. But are you saying that you use old strings like a file to cut the slots after making some sort of groove with, let's say, a cutting-tool like a sharp knife or blade?
I think that this may work with the slots for the E, A and D string because those strings are wounded. But how about the other unwounded strings? You can't 'file' with an smooth string...
Or am I completely wrong?