What do you do when you want to fit a full carbon threadless fork to an older Giant frame which used an internal 1″ threaded headset?
The Giant frames of this era used an internal bearing threaded 1″ headset, and a threadless version is not available. In order to fit a full carbon 1″ fork it was necessary to either replace or modify the existing threaded bearing cone.
We chose to modify the existing headset cone rather than machine a new one.
In the photos you can see that the internal threads of the cone were removed so that the internal diameter is 0.05mm larger than the largest radius of the fork’s steerer tube. The threads are not completely removed but the surface area remaining is more than enough to correctly support the cone, and by completely removing the thread the internal diameter would be too big and the cone would not locate correctly on the bearing.
The external hex used to tighten the threaded cone was also removed and the external diameter is identical to the headset spacers which are to be used, thus having a visually clean appearance.
In order to tighten the headset we opted to machine a custom sleeve which would be epoxied inside the steerer tube of the fork, like an Alpha Q. The custom sleeve features a 1.5mm wall thickness, counter-bores at each end to save weight, and a one-piece threaded center section. It is 40mm long so as to support the stem area over a wide range of adjustment.
The topcap was also custom machined to fit the radius of the stem, and to give a clean appearance.
The topcap and sleeve weigh 31 grams which is considerably lighter than a standard 1″ expander plug.
What appear in the photos to be imperfections are in fact the remnants of coolant from the machining processes.