3D Printing Design Guide
Layer-based design rules: orientation, supports, wall thickness, overhangs, tolerances
Additive manufacturing builds parts layer by layer from a 3D model. Because material is deposited or sintered incrementally, design rules revolve around layer resolution, self-supporting geometry, anisotropy and thermal shrinkage — rules that differ substantially between FDM, SLA, SLS/MJF and DMLS. Understanding these four families lets an engineer design once for the cheapest viable process.
1. Process families and resolution
FDM (material extrusion) has layer heights of 0.1–0.3 mm and typical tolerance ±0.5% (±0.5 mm), sufficient for fit-check prototypes. SLA (vat photopolymerization) reaches 0.025–0.1 mm layers with ±0.2% (±0.2 mm) tolerance and the best surface of any plastic process, suited to visual and flow-test parts.
SLS and MJF sinter nylon (PA12) powder: layers 0.1–0.12 mm, tolerance ±0.3% (±0.3 mm), no support structures for most geometries, and good isotropy. DMLS prints metal (316L, AlSi10Mg, Ti-6Al-4V, Inconel 718) with layers 0.02–0.05 mm and mechanical properties near wrought material.
2. Walls, overhangs and supports
Minimum wall is process-dependent: ~0.7–1.0 mm for SLS/MJF, 0.8 mm for FDM, 1.0 mm for SLA resins; below these, walls warp or delaminate. Overhangs beyond 45° from vertical generally need supports in FDM/SLA/DMLS, which leave witness marks and add removal cost; orient parts to keep critical faces away from supports.
In SLS/MJF un-sintered powder supports geometry for free, so complex lattices and internal channels print without extra cost — a decisive advantage for ducts, manifolds and lightweight brackets. Keep channel diameters ≥ 4 mm to allow powder removal.
3. Orientation, anisotropy and warpage
Layer bonding is weaker than in-plane material: printed parts are anisotropic, and tensile strength across layers is typically 80–90% of in-plane values for polymers, less for some resins. Orient the most-stressed direction along the build plane where possible.
Large flat areas cool unevenly and curl; keep large faces small, use lattice or ribs, and expect some edge lift on FDM. DMLS parts carry residual stress — annealing/heat-treat options exist per alloy and relieve distortion on thin features.
4. Features that print well
Internal channels, lattice infill, snap fits (with correct strain limits), living hinges in TPU, bosses with ≥ 0.5 mm wall and embossed text above 0.5 mm depth all print reliably. Text smaller than 0.5 mm, very thin walls, sharp internal corners and unsupported bridges do not.
Design for the layer: choose layer-aligned hole axes, avoid horizontal blind holes that trap powder or resin, and specify post-processing (media blasting, sanding, dyeing) on the drawing when cosmetic surfaces matter.
Quick reference
| Process | Layer height | Typical tolerance | Min wall | Notes |
|---|---|---|---|---|
| FDM | 0.1–0.3 mm | ±0.5% / ±0.5 mm | 0.8 mm | Supports required; cheapest |
| SLA | 0.025–0.1 mm | ±0.2% / ±0.2 mm | 1.0 mm | Best surface; resin brittle-ish |
| SLS / MJF | 0.1–0.12 mm | ±0.3% / ±0.3 mm | 0.7 mm | Self-supporting; PA12 |
| DMLS (metal) | 0.02–0.05 mm | ±0.2% / ±0.2 mm | 0.4 mm | Near-wrought strength; stress relief |
Sources & references
- ISO/ASTM 52900:2021 — Additive manufacturing general principles
- ASTM F2924 — DMLS Ti-6Al-4V specification
- ASTM F3184 — DMLS 316L specification
- Xometry Learning Center — 3D Printing Design Guide (public engineering reference)