First of all, thank you for this information!
Secondly, for anyone who tries this with a drill press (as I did), don't go straight for the 4mm bit. I did that and ended up destroying a head. Start about 4 bit sizes smaller, and bore each hole
slowly until you get to the 4mm bit.
A question for you xMackx, in the picture above you say not to have the
coils close enough to touch, but in
this post you say you
do want the
coils touching. You also said you explain "more on this phenomena in another thread". I'm currently looking through your history but I can't seem to find the thread in question. So my question is, should I have them touching or not?
I should add that I'm using cotton balls, which are working amazingly thanks to your hole suggestion.