Ken, I was thinking about what you said about the magnetic field not going through the brass, and was curious- did a little reading and a little experiment. I was able to hold a thin sheet of brass to the fridge with a kitchen magnet, which was not too powerful, so it seems maybe there is enough field getting through to be useful. My reading suggests that brass behaves like air or paper with respect to static magnetic fields, it has a low magnetic "permeability", so it shouldn't block a static magnetic field, but it is a conductor, so it will block oscillating electro/magnetic fields as they will just set up eddy currents in the brass. I'm wondering if you know if the magnetic chucks use static permanent magnets or electrically generated oscillating magnetic fields?