I have the brass knob directly on the copper tab and washers around the guitar pic. The power runs through the copper to the brass then down the post. Any washers between are only gonna increase resistance! The heat is deffinatly caused by build up in the threads. Clean the post the female thread of the brass and the flat contact surfaces. I have been using glases wipes which smell like ISO but a damp paper towel would do... Normally have to do this every 6 weeks or so but is pretty much the only maintenance I ever have to do !