Howdy,
I agree that 1/64 isn't much on a flat plane but, when you add the 10 degree up angle the open end of the top plate gets a sharper angle. The biggest advantage and the greatest efficiency to a square, straight, or flat filing or grinding is chip flow. Otherwise known as splitting hairs with most folks. Anyways, the best way to optimum chip flow is a flat edge. No matter what you do with a round file, the top plate edge is going to be concave and it makes the chip curl, or crinkle. When you use a chisel file you're creating flat edge which produces a clean flat chip that flows. The goofy file is the link between round, and square filing. It gives you a good flat edge on the top plate but, goes back to a round hook on the side plate for severing. You can actually do a goofy grind using most round grinders just by dressing the wheel. You dress the wheel like you normally would with the half round shape. Now, lay the head angle over as far as it'll go, and the chain vise at zero. Lay your dressing brick on the chain vice rails and introduce the wheel. Dress the wheel until the dressed area intersects the centerline of the wheel. You basically end up with a 90 degree radius instead of 180 degrees. The whole thing you're try to accomplish is to get the whole top plate on to the side of the wheel. This will give you a flat edge on the top plate. When you move to beveled chisel file, or a square grinder you're creating a flat edge on the top, and side of the tooth for the ultimate in chip flow, and side plate severing.
Regards
Gregg
