Dirt Jumper V1: 12 days to Sea Otter 2025

I designed this dirt-jump frame and built it, with help from friends, in the 12 days before Sea Otter Classic 2025: Nylon 12 lugs bonded to carbon fiber tubes. I designed the lugs in Fusion 360, using its surface modelling tools for the head tube lug.

To check fit, I printed a PLA head tube lug and test tubes to compare tolerances between print methods, machined test tube fittings on the lathe, and test-fitted the headset bearings. On day 4 I realised FDM and resin prints probably wouldn't be accurate enough. The final lugs were SLS printed on a Formlabs Fuse 1.

In the bonding process we ran into our biggest issue: the cranks hit the bottom bracket lug, so they didn't really fit. We bonded the lugs to the tubes on day 11, and the bike was at Sea Otter on day 12. The interest in the printed lugs caught me off guard, and the bike was later featured in Pinkbike, Bikerumor and All3DP.

It's a proof of concept, not a frame for dirt jumping: it can be ridden for a short, flat ride, but the PA12 lugs let it flex a lot sideways. Afterwards I released the design as an open-source frame under a Creative Commons Attribution 4.0 license.

After Sea Otter I redesigned the frame as Dirt Jumper V2 and built it two ways: with CNC-machined junctions on carbon tubes and 3D printed almost entirely in aluminum.