Perhaps you didn't see one of the earlier threads on this subject, where welding the two pieces together was discussed, or where
making the shaft one piece was discussed. The shaft is 12mm at the DD joint and the bearings, and 1/2" (12.7mm) at the other end. So, you need to braze it with the shaft installed in the bearings and the end mounting block. I would hesitate to do that....the heat would probably be hard on the bearings! plus you can't disassemble it without reheating and melting the braze.