Design & Engineering
Design Right, Print Right
Great 3D prints start with great design. Whether you're designing for SLS or FDM, these practical guidelines will help you avoid common pitfalls and get production-ready parts on the first attempt.
Designing for 3D printing is different from designing for CNC machining or injection molding. Each process has unique constraints and advantages. This guide focuses on practical, actionable rules, primarily for powder-bed processes like SLS (Selective Laser Sintering), but many principles apply broadly across additive manufacturing technologies.
Wall Thickness
Wall thickness is the single most common source of print failures. Too thin and your part warps, cracks, or fails to resolve. Too thick and you waste material and risk internal stress.
| Feature | Minimum | Recommended |
|---|---|---|
| Structural walls | 0.8 mm | 1.2–2.0 mm |
| Unsupported walls | 1.0 mm | 1.5–2.0 mm |
| Large flat panels (>50 mm) | 1.5 mm | 2.0–3.0 mm |
| Embossed/engraved text | 0.5 mm depth | 0.8–1.0 mm depth |
Pro tip: If your part has large flat surfaces, add subtle ribs or a slight curvature on the underside to prevent warping during the cooling phase.
Overhangs & Self-Supporting Angles
For SLS, overhangs are less of a concern because unsintered powder acts as natural support. For FDM, overhangs beyond 45° from vertical typically need support structures, which leave surface marks and require post-processing.
Guidelines by Process
- SLS (Nylon): Nearly unlimited geometry freedom. Trapped powder in enclosed cavities is the main concern—add escape holes (≥3 mm diameter) to hollow sections.
- FDM: Keep overhangs under 45°. Use chamfers instead of fillets on bottom edges. Orient parts to minimize support needs and to put load perpendicular to layer lines for best strength.
Tolerances & Fit
3D printing is not as dimensionally precise as CNC machining. Expect typical tolerances of ±0.3 mm for SLS and ±0.5 mm for FDM. Design your fits accordingly.
| Fit Type | Gap per Side | Use Case |
|---|---|---|
| Press fit | 0.0–0.1 mm | Permanent assemblies |
| Snug / sliding fit | 0.2–0.3 mm | Lids, caps, enclosures |
| Loose / clearance fit | 0.4–0.5 mm | Rotating or moving parts |
Pro tip: Always prototype critical fits before committing to a production run. Print one test piece, measure it, and adjust your CAD model based on actual results.
Holes, Slots & Channels
Small holes tend to print undersized in most 3D printing processes due to thermal effects and layer resolution. Plan for this.
- Minimum hole diameter: 1.5 mm for SLS, 2.0 mm for FDM. Smaller holes may close up during printing.
- Vertical holes (parallel to build direction) are more accurate than horizontal holes, which can become slightly oval.
- Threaded holes: Print undersized pilot holes and tap threads after printing, or design for heat-set inserts (recommended for repeated assembly).
- Internal channels: Keep diameters above 4 mm for reliable powder evacuation in SLS. Use teardrop-shaped cross-sections for horizontal channels in FDM.
Text, Logos & Embossing
Adding text or logos to printed parts is common for branding, labels, and identification. Follow these guidelines for readable results:
- Minimum font size: 8pt for embossed (raised) text, 10pt for engraved (recessed) text.
- Use bold, sans-serif fonts. Thin serifs and fine details may not resolve clearly.
- Depth/height: At least 0.5 mm for embossing, 0.8 mm recommended. Engraving should be at least 0.5 mm deep.
- Orientation matters: Text on the top surface (facing up during build) produces the crispest results.
Snap Fits & Assembly Features
3D-printed snap fits work well with flexible materials like PA12 nylon (SLS) but require careful design:
- Cantilever snaps: Keep the beam length at least 5× the wall thickness. Longer beams flex more gently and are less likely to break.
- Deflection: Design for no more than 2–3% strain at maximum deflection for nylon parts.
- Fillet the base of snap-fit beams to prevent stress concentration and cracking.
- Living hinges: Possible with SLS nylon but limited lifespan. Design them at 0.4–0.6 mm thickness for best flexibility.
Common Mistakes to Avoid
Walls thinner than 0.8 mm
Thin walls warp, curl, or fail to sinter properly. They also break easily during post-processing and shipping.
No escape holes in hollow parts
Trapped powder in SLS parts adds weight, increases cost, and can cause uneven mechanical properties.
Designing for CNC tolerances
Expecting ±0.05 mm tolerances from 3D printing will lead to disappointment. Design for ±0.3 mm and post-machine critical features if needed.
Ignoring build orientation
3D-printed parts have anisotropic properties, meaning they're weaker between layers. Orient critical load paths along the XY plane when possible.
Sharp internal corners
Sharp corners create stress concentrations. Add fillets of at least 0.5 mm radius to internal corners for improved durability.
Pre-Print Design Checklist
All walls ≥ 0.8 mm (1.2 mm recommended for structural parts)
Escape holes (≥ 3 mm) in hollow sections for powder evacuation
Tolerances set to ±0.3 mm for SLS, ±0.5 mm for FDM
Holes oversized by 0.1–0.2 mm to compensate for shrinkage
Text is bold, sans-serif, ≥ 8pt, with ≥ 0.5 mm depth
Snap-fit beams have fillets at the base
No trapped volumes or fully enclosed cavities
File exported as watertight STL or STEP with correct units
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