Centering the Fork Crown
After the blades are raked and the fork ends are brazed in, you measure the blade seat of your crown and cut the overall length of your fork blades +1mm. Then you dry fit the blades into the fork crown, and put a reference wheel into the fork subassembly to gauge the crown alignment. Sighting through the empty steerer port, you can easily see if things are misaligned. Whichever side of the rim has more clearance is the SHORTER fork blade, so file 0.2mm or so off the other blade. Recheck. Iterate until the alignment looks good. If the oval of the fork blade is not aligned to parallel the wheel, you can use the fork crown to try to torque it straight as well.