FDM or SLS gears: load, layers and material

A broken tooth alone does not identify the failure cause or the right repair process. We review the profile, shaft mounting, mating gear and operating conditions. Those details guide material and orientation selection.

Loading at the tooth root

At the tooth root, we review section size and stress concentration. Flank contact, wear, backlash, misalignment and jamming also matter. One photo of the broken part does not establish which mechanism caused the failure.

What does this layer structure do

A spur gear printed flat with its shaft axis in Z has its tooth profile in the X/Y plane. Tooth bending does not then automatically mean pulling layers apart in Z. Gear type, force direction, face width, hub, toolpaths and layer bonds change the assessment. Rotation alone does not replace that review.

Sintering also has its own direction

SLS also builds layers. The PA12 TDS gives elongation at break of 11% X/Y and 6% Z (ASTM D638 Type 1). These results do not set rotations to failure or tooth strength. See the PA12 sheet and the orientation guide.

Root fillet and material selection

The tooth-root radius and correct profile matter, but do not replace material selection. Notched Izod: PA12 32 J/m and PA11 71 J/m (ASTM D256-10). A specimen impact test is not a gear fatigue test. PA11 may be a candidate for impact loading; pricing, availability and production conditions require individual confirmation.

The heat no one asks about at the start

Give temperature at the part and operating duration rather than judging a housing by touch. HDT at 1.8 MPa: PA12 87 °C and PA11 46 °C (ASTM D648). This is a specimen's specified deflection temperature in a test, not a gear service-temperature rating. Lower temperatures still require review of force, duration, geometry and environment.

What you won't find in this article

We do not have one strength value for all FDM or a service-life result for any SLS gear. Data sheets describe materials and standardized tests. Agree requirements and inspection for the selected model; the brief needs torque or force, speed, cycles, lubrication, temperature and an assembly photo. Compare FDM and SLS.

When nylon is the wrong choice

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  We do not replace a high-torque steel gear with nylon based on geometry alone.
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  Gears operating above 87 °C under load are outside this repair service. This is a service-scope boundary; HDT does not confirm every part below it is suitable.
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  Very fine tooth profiles need review and a trial. Gear module alone is not a printing-resolution limit; SLA or machining also needs material selection.
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  We do not accept safety-critical parts, including steering, braking or lifting people.

Service scope and reconstruction information are on the gear page. Send photos and a description; missing dimensions and a fit trial are agreed before scope confirmation.

Sources: Nylon 12 TDS (PDF), Nylon 11 TDS (PDF), Sovol: FDM gear orientation.