Rather than buying carbon forks and plonking them on my new bike, I really had to build my own.
The fork crown and dropouts were relatively easy using the method for forged carbon lugs I’ve been developing for a while now. For the blades/legs however, aluminium extrusion wasn’t readily available in the shape I wanted (~15 x 40mm), so this was a great excuse to build hollow carbon blades.
Hollow parts like these are usually built using pre-preg carbon fibre and cured in an oven under vacuum. Pre-preg carbon fibre is expensive, a little hard to come by, and vacuum bagging uses a lot of consumables which I’d rather avoid. So I set about developing a more resourceful method to build these using more accessible materials and methods (woven and uni-directional carbon cloth).
Starting with a bike inner tube with a carboard mandril inside, the carbon weave (a combination of 200 GSM plain weave and 300 GSM unidirectional) is wet out and wrapped around the inner tube. This layup went in a 3D printed split mould, the ends plugged, and the tube inflated to 50 PSI while the epoxy cures.
After having built all the lugs and the two blades required, it was then time to assemble the forks. Using a 3D printed jig to keep everything on the straight and narrow, the fork crown (with steerer tube already incorporated during production of the part) was bonded to the two dropouts and a separate brake post. Aluminium washers and an axle thread were finally glued in to the dropouts. Once clear-coated, the finished forks weighed in at a grand total of 600g. So not the lightest when compared with carbon road forks, but not too shabby for a first run at custom built gravel forks! For comparison, most suspension forks will weigh a little over 2kg.
