Your leaf springs start as flat bars of SAE 5160 High Alloy Spring Steel, cut to size. We heat the ends of the main plate and roll the eyes. Then heat the ends of the other leaves to roll and taper the ends, which reduces hysteresis.
This is key to a good, smooth riding suspension. we then measure, mark then punch the hole for the center bolt, which holds the leaves together and locates the spring on the axle.