Hardtail
Finished 4/21/24
The goal here is to have a do it all hardtail. It has a geometry that let's it handle technical single track confidently while not getting bogged down in long pedaled miles. Like the All-Road, I'm choosing to keep standover height a little higher than most production frames so it can tackle some multiday routes/races without storage worries.
Some challenges:
Clear a 29x2.4" tire (or 2.6" if possible) using custom bent and dimpled chain and seat stays and a bent seat tube.
Adjusting fixturing to accommodate UDH dropouts. SRAM has specific requirements for the Transmission groupset to function properly. Unlike typical dropouts, UDH placement is asymmetric.
Incorporating internal routing for a dropper post.
Currently, I've finished up the seat post. I milled out a 3/8" slot to incorporate a plastic housing guide to internally route the seat dropper. The piece on the right will be brazed on for reinforcement.
As of the end of the winter quarter, the front triangle is mitered and fit up in the jig.
Bending and dimpling tubes to get clearance for the tire and chainring was a big design hurdle. I opted to CNC this half yoke to get that clearance and make the build process a little easier.
With Jake's help, we cut this out of 4130 in three ops and one other for cutting soft jaws. The final miter to fit to the bottom bracket was done on a 2 axis CNC Bridgeport.
Typically a tube is bent and dimpled to create clearance for the tire and chainring. Both tube and yoke are fixed at the bottom bracket junction with equal loads in the +z direction.
Improper dimpling can create a significant stress riser and further bends the tube, making it a little more difficult to manufacture as designed.
The machined yoke is far stiffer and stronger but about 3 times the weight (~43g vs 118g). It could be made lighter if done as two holllowed parts.
The big advantage is ease of assembly and fixturing along with significantly more clearance for larger tire and chainring combinations.
Break in ride on the Tour de Los Padres "Tour" route
Fully loaded with ~20-30lb of gear
Ended up being my partners bike, powder coated in peach