To install a new fork with a 1.125″ steer tube in a Giant TCX OverDrive frame (headset is designed for a 1.25″ steertube) I made a custom crown race. The crown race needed an ID of 30mm and an OD of 43mm with a 45° chamfer for the bearing to rest on. First I designed the crown race, top of the fork and the bearing in Autodesk Fusion 360. I created an assembly to ensure the crown race would fit both the bearing and the fork. I then 3D printed it in ABS for a test fit. Finally I turned the crown race out of 6061 aluminum on my CNC converted 9×20 lathe.