In general, first cut the workpieces of the right size, then you need to make a cube from the initial cutting of the rod (it is not necessary to try very accurately, 1-3 mm inaccuracy is not terrible), then the cube alternates edges and protruding corners until it becomes faceted but more or less round, without strongly protruding angles. Beat to try with equal force on different sides, if somewhere stronger somewhere weaker then you get an oval, but you can always heat it up again and fix it.
