Printed Gears and Bushings in Carbon Fiber Nylon: What Actually Holds Up

A stripped gear or a wallowed-out bushing is the kind of failure that takes a whole assembly out of service. Printing replacements in carbon fiber nylon usually works — the failures we see almost never come down to the material. They come down to orientation, clearance, and picking the wrong nylon for the load.

Where carbon fiber nylon gears actually stop working

Carbon nylon is a good fit for timing gears, idler wheels, low-speed drive gears, fan hubs and linkage bushings. It is not a fit for anything that takes shock loads or sends full motor torque through a single tooth. The limits we hold to in the shop: gears under about 60mm diameter, under 2Nm, a few hundred RPM, clean environment. Past that you are testing the part in service instead of on the bench.

Orientation is the whole game

Print a gear flat, axis vertical, teeth in the XY plane. Tooth bending load then runs in-plane along the extrusion lines, which is the strong direction. Stand the gear up on its face with the axis horizontal and you are pulling teeth apart at the layer bonds — it shears off on the first real load. Same rule for bushings: axis vertical, so hoop stress stays in-plane.

Clearances and post-work

Carbon fiber nylon prints slightly oversize on bores and shrinks as it cools. Add 0.2–0.3mm of clearance on a slip fit, then ream or drill the bore to size after printing. Chamfer the bore entry 0.3mm. For the teeth, use a proper involute model with 0.1–0.15mm of backlash — a printed tooth that comes out tight will bind and eat itself inside an hour.

Settings that hold up

What we run on PA6-CF for gears: 0.2mm layers, 0.6mm hardened nozzle, 290°C nozzle, 100°C bed, 50–55°C chamber, 5–6 walls, 50% cubic infill, part cooling off after layer 3, 60mm/s. Dry the spool to under 15% RH first — 80°C for 8–12 hours. Wet nylon prints foamy, and foamy gears strip. For bushings, PA12-CF at 270°C nozzle, 90°C bed, 4 walls, 60% infill reams clean and runs smoother against a steel shaft.

One more thing: carbon fiber nylon is abrasive. A CF gear meshing with a steel pinion will polish that pinion down over months of running. Grease both, and keep a spare on the shelf.

What We Use

For gears we load TINMORRY PA6-CF — the toughest carbon nylon we keep on the rack, and the one that survives tooth loading. For bushings and anything that has to slide, IEMAI PA12-CF machines and reams cleaner, and the tested temps and bed prep are on the product page.

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