Design for
better prints.
Follow these guidelines to get the best results from FDM 3D printing. Small design choices make a big difference in print quality, strength, and cost.
Quick Reference
Wall Thickness
Walls define the outer shell of your print. Too thin and the model becomes fragile or fails to print. Too thick and you waste material and time.
At 0.4mm nozzle width, use at least 3 walls for structural integrity. This ensures the slicer can fill the wall properly.
Parts that bear load or need durability should use thicker walls. 5 perimeters (2.0mm) is a good starting point.
Single-perimeter walls are fragile and may not survive removal from the build plate or post-processing.
Overhangs & Supports
FDM prints layer by layer from bottom to top. Any area that extends outward without material below it is an overhang. Beyond 45 degrees, you need supports.
The 45-degree rule: each layer can safely extend about 50% of its width beyond the previous layer without supports.
Chamfers create a controlled 45-degree angle that prints cleanly without supports. Fillets at the base of a model often need supports.
Support structures touch your model and leave blemishes when removed. Design to minimize supports for the best surface finish.
Bridging
Bridges are horizontal spans between two raised points. FDM can bridge small gaps by stretching filament across, but longer bridges sag or fail.
Short bridges sag slightly but are usable. The extruder stretches the filament across the gap in a single pass.
Rotate your model on the build plate to minimize bridge length. A 20mm bridge in one orientation might be only 5mm in another.
Long bridges will sag significantly, string, or fail entirely. Use supports for spans over 20mm.
Print Orientation
How you orient a model on the build plate affects strength, surface quality, and support usage. Layer lines are the weakest axis — parts break between layers.
Layer adhesion is weaker than the filament itself. If a part will be under tension, orient it so the force runs along layers, not pulling them apart.
The side touching the build plate is the smoothest. Orient your model so the most visible face is against the plate.
Each layer takes time. Laying a model flat reduces total layers and therefore total print time. This also reduces the chance of print failure.
Tolerances & Fits
FDM parts are slightly oversized because the extruded filament expands. If you're designing parts that fit together, you need clearance.
| Fit Type | Clearance | Example |
|---|---|---|
| Press fit | 0.0 – 0.1mm | Pins, pegs |
| Snug sliding | 0.1 – 0.2mm | Lids, caps |
| Free sliding | 0.2 – 0.4mm | Drawers, rails |
| Loose fit | 0.4 – 0.6mm | Hinges, axles |
Holes parallel to the build plate are stretched by gravity on the top arc. Compensate by designing them 0.2–0.4mm undersized.
Infill Density
Infill is the internal structure of your print. Higher infill means more material and stronger parts, but also more time and cost.
STL File Preparation
A clean STL file is the foundation of a good print. These checks prevent the most common print failures.
No holes in the mesh. Every edge connects exactly two faces. Non-manifold meshes confuse slicers and produce broken toolpaths.
Flipped normals cause the slicer to interpret inside as outside. Most CAD software exports correctly, but always verify.
STL files don't store units. Set your CAD software to millimeters before exporting. A 25mm cube should show as 25 units in the file.
Binary STLs are 3-5x smaller with identical geometry. ASCII is only needed for debugging.
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