Minimum features by process.
| Process | Min wall | Min hole | Min embossed text | Min engraved text |
|---|---|---|---|---|
| SLA (standard resin) | 0.5 mm | 0.5 mm | 0.5 mm × 0.4 mm | 0.3 mm × 0.4 mm |
| SLS (PA12) | 0.8 mm | 1.0 mm | 0.8 mm × 1.0 mm | 0.5 mm × 0.5 mm |
| MJF (PA12) | 0.5 mm | 0.5 mm | 0.5 mm × 0.5 mm | 0.4 mm × 0.4 mm |
| FDM (ABS/PC) | 1.2 mm | 2.0 mm | 1.0 mm × 1.5 mm | 1.0 mm × 1.0 mm |
| DMLS (metal) | 0.5 mm | 1.0 mm | 0.8 mm × 0.5 mm | 0.3 mm × 0.5 mm |
| PolyJet | 0.6 mm | 0.5 mm | 0.5 mm × 0.3 mm | 0.3 mm × 0.2 mm |
Every process has a minimum feature size — walls, holes, text, fins. Below the minimum, features either won't print or won't survive post-processing.
How parts sit in build matters.
Most accurate
Vertical walls (parallel to build Z-axis) have best accuracy and surface finish. Prioritize critical features in this orientation.
Down-face rougher
Down-facing horizontal surfaces (held up by support) have poor finish. Up-facing surfaces are smooth.
Vertical preferred
Holes with axis vertical to build print round and accurate. Horizontal holes (axis along build direction) can be elongated.
Weaker in Z
Most 3D printing is weaker in Z direction (between layers) vs XY. Orient with critical loads in XY plane when possible.
Tall = slow
Print time is proportional to height in Z. Short, wide parts print faster than tall, narrow ones — lower cost.
Large flat bottoms
Large flat bottoms warp during cooling. Break up with support ribs or fins, or orient differently.
Build orientation affects surface finish, mechanical properties, and feature accuracy. The same part printed in different orientations can look and perform very differently.
Overhangs need support.
Self-supporting designs
Problematic designs
What 3D printing can actually hold.
| Process | Typical tolerance | Critical feature | Post-machining improves to |
|---|---|---|---|
| SLA | ±0.1 mm | ±0.05 mm on small | ±0.025 mm (CNC) |
| SLS | ±0.2 mm | ±0.1 mm | ±0.025 mm (CNC) |
| MJF | ±0.15 mm | ±0.05 mm | ±0.025 mm (CNC) |
| FDM | ±0.3 mm | ±0.2 mm | ±0.05 mm (CNC) |
| DMLS | ±0.2 mm | ±0.1 mm | ±0.025 mm (CNC/grind) |
| PolyJet | ±0.1 mm | ±0.05 mm | N/A (fragile) |
Tolerance expectations per process — match your design tolerances to process capabilities.
FAQ
Quick decision framework: (1) Visual prototype with fine detail → SLA. (2) Functional nylon prototype → MJF (best surface) or SLS (more materials). (3) Large parts → Industrial FDM. (4) Aerospace materials → FDM Ultem 9085. (5) Full color/multi-material → PolyJet. (6) Metal parts → DMLS (titanium, Inconel, aluminum). (7) Production quantities → MJF for nylon, SLS for specialty materials. Each has trade-offs between cost, speed, material, and tolerance.
Sometimes. MJF and SLS nylon meet production-grade mechanical properties for many applications. DMLS metal parts with appropriate post-processing (heat treatment, HIP) meet aerospace and medical standards. SLA and PolyJet are typically prototype-only (brittle, UV-degradable). Specifically: FDM Ultem 9085 is certified for aircraft interior (production), MJF PA12 is used in consumer products at volume, DMLS Ti Gr.23 is used for medical implants.
Varies by process. SLA can print 0.5mm walls for small parts. SLS needs 0.8mm minimum. MJF: 0.5-0.8mm depending on orientation. FDM: 1.2mm minimum (layer width dependent). DMLS: 0.5mm possible with careful orientation. Always check with provider — minimum wall is specific to machine and material. For walls at minimum, post-processing (support removal, cleaning) risks damage.
Hollow parts save material and time — major cost benefit. Design considerations: (1) Wall thickness ≥ minimum for process, (2) Drain holes for resin/powder removal, (3) Support structures inside hollow (may be impossible to remove). For DMLS metal parts, hollow with lattice infill is standard — reduces weight and cost. For SLS/MJF, hollow with interconnected chambers must have drain paths to remove unsintered powder.
Depends on end use. If design will transition to injection molding or CNC for production, design for final process — 3D print the design for prototype validation. If design is always 3D printed (production volumes <500, or geometry impossible to mold/machine), design for 3D printing: lattices, internal features, consolidated assemblies. The advantage of 3D printing is design freedom not possible in molding — use it where value exists.
Post-processing often 20-100% of print cost. Basic: support removal + bead blast = 20-30% of print cost. Intermediate: vapor smoothing or painting = 50-80%. Advanced: CNC finishing of critical features + paint = 80-150%. For functional parts, calculate total cost including needed post-processing. For cosmetic prototypes, post-processing often exceeds print cost but necessary for presentation quality.
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