I'm trying to make most of an engine from scratch (cylinder, crank case, piston). I've been reading about pistons and I've learned that many modern pistons are cam ground--slightly elliptical in shape (reference article). As I currently understand it, the reason for this is so that when the piston heats up to the operating temperature, it forms a more precise circular shape.
I only have access to a metal lathe and that got me thinking, is it possible to design pistons so that they can be machined circularly and they expand evenly? It seems that it would save on manufacturing costs; then again, why aren't modern pistons designed so they don't have to be cam ground and that they expand uniformly?