"A simple, shop-made tool like this is my favorite for boards up to 4/4 thickness. It also is nice to use in the metal shop as well for scribing center on tube and bar stock. http://lumberjocks.com/projects/141225"
"Typical rule of thumb is to cut no deeper than the bit is wide, thus a 1/4" end mill you would cut no deeper than 1/4" per pass. This is all dependent on your feeds and speeds of course. I personally like to cut only half of the diameter deep per pass and crank up the feed a bit, it allows for better chip clearance and longer end mill life."