LOL
And round track blades are much easier to sand down. Much less hand-eye coordination needed. For oval, there's a tendency to grind too much off the major axis (front and back of the blade) and less off the sides, if you just hold the dynafile steady. So you have to vary the pressure on the dynafile in time with the rotation, to make yourself grind more off the sides, to keep it even. And know you're not going to be perfect at it, so account for the fact that there will be thicker and thinner places, where you didn't grind it exactly evenly. So leave a little more safety margin than you might have to in a perfect world.

It helps to grind at a 45° angle to the rotation axis (or any angle really, other than 90°). Switch sides now and then, from 45° left to 45° right, so the scratches cross each other -- then you can see when the first set of scratches just starts to disappear.

But why am I describing this crazy procedure that no one is ever going to do (if they're smart)?