Eagle has two Haas VF3 CNC machining centers that we use to do all sorts of custom machining to crankshafts. One very popular process is pendulum undercutting. This process removes material from the counterweights to reduce the weight of the crankshaft, but not on the outer edge so that the bobweight of the crank is hardly affected if at all. You can have a lighter crank and still balance it easily with typical connecting rods and pistons.