Strong, Functional Prints

The single biggest mistake in functional printing is cranking infill to 100%. For most parts, perimeters (walls) carry the load, not infill. Going from 3 to 5 walls strengthens a part far more — and faster, and lighter — than raising infill from 20% to 60%.

Think of it like a tube: the outer shell does the work. Add walls and top/bottom layers first; reach for high infill only for solid, compression-loaded parts.

Infill mostly resists compression and ties the walls together. For functional parts:

• 15–25% is plenty for most uses
• 40–60% for parts under real stress
• Patterns matter: gyroid is strong in all directions and great for flexible loads; grid/cubic is fast and strong for general use; honeycomb is strong but slower

More infill adds weight, print time, and heat — with diminishing returns past ~50%.

FDM parts are anisotropic: strongest within a layer, weakest between layers. A hook printed lying flat is far stronger than the same hook printed standing up, because the load pulls along the layers instead of peeling them apart.

Orient the part so tension and bending act along the layer plane. If a part must be strong across layers, raise the print temperature slightly and slow down to improve inter-layer bonding, or choose a material with better layer adhesion.

Geometry only goes so far — material sets the ceiling:

• PETG: tougher and more impact-resistant than PLA, good all-round functional choice
• ABS/ASA: heat- and impact-resistant, needs an enclosure
• Nylon / PA-CF: high strength and durability for demanding parts (and a hardened nozzle)
• PLA: stiff and strong in tension but brittle and heat-sensitive — fine for light-duty

Match the material to the load, temperature, and environment the part will actually see.