Copied from http://fab.cba.mit.edu/content/processes/PCB/modela2.html
The modela is a nice little milling machine that cranks out most of the circuits you will need for HTMAA. To be able to mill on it, you need to have FR1 which is a paper based copper plate. You cannot mill the fiberglass copper plates on the modela as it will break your bit and the dust it will create is irritant. The FR1 is more tan than the fiberglass, which is more green, and the FR1 is in stock in 016 in 2x3 inch and 4x6 inch pieces.