If starting with a square blank, draw a line across one of the diagonals. Mark the center and mark two spots to each side of center along the diagonal. Label the two off center marks A and B. Duplicate this on the other end of the blank (make sure to use the same diagonal). Now mount the blank using the A marks as center. Turn it down until about half the blank is rounded and then mount using the B marks as center. Turn until the two halves are even. That will give you an oval.
