Originally Posted by
HillRider
Probably an easier way to make the 1-1/8" crown race fit would be to make a short bushing as you specified and use a 1" crown race setter to drive it into place and then set the 1-1/8" crown race on it. BTW. wouldn't the ID be 26.30 or 26.35 mm to be a snug fit on a 26.4 mm crown race seat?
Yes, that's exactly what I had in mind. the 26.0 dimension was a typo, I meant 26.4. You don't have to make it undersized because in normal conditions the crown race is at the nominal and the fork's crown seat is a bit over for interference. Making the ID under would be excessively tight.
Note that the adapter race needs a flange at the bottom, because you can depend on the flat seat on the fork being wide enough.
BTW- I used to have 1" adapter crowns for Cane Creek 1-1/8" headsets. If the Columbus crown race (actually centering cone) is similar, I can check to see if I still do. That and a Thomson 1" adapter and the OP could be set.