3D-printed bicycle gearbox made of PLA passes practical test surprisingly well

The YouTuber “Well Done Tips” has manufactured a complete bicycle gear system from PLA – and contrary to all expectations, the system can withstand cycling. Anyone familiar with the stresses and strains of a bicycle drive system knows that chains and sprockets in particular are exposed to enormous torques. It is surprising that a thermoplastic material such as polylactide (PLA) can withstand these forces.

The design was modeled entirely in Fusion 360 using an automatic gear tool. These are simple spur gears mounted on a steel axle. The hobbyist uses standard skateboard ball bearings for the bearings – made of steel, not printed. The entire system is based on a fixed gear ratio, which further increases the load. Despite these limitations, the maker achieved a speed of around 20 km/h during his test.

A decisive factor for durability is likely to be the comparatively large width of the gears. This increases the contact area and distributes the forces better. The drive pinion on the rear wheel was partially reinforced with a steel part from the original cassette, as the flat grooves of the freewheel hub were unsuitable for PLA. During the test ride, a squeaking noise occurred – possibly due to a lack of lubricant or the straight tooth profile. Switching to helical teeth could remedy this.

Although the experiment shows that PLA can withstand higher loads in the short term, the material remains unsuitable for functional drive elements. Studies and practical experience show that PLA wears quickly under friction and heat. Nylon or carbon fiber-reinforced filaments would be significantly more robust for permanent applications.