3D Printing Tolerances & Design Rules: FDM vs SLA vs DLP

Designing for 3D printing is not the same as designing for CNC or injection molding. Each additive technology — FDM, SLA, and DLP — has distinct capabilities and constraints that directly impact dimensional accuracy, minimum feature sizes, and achievable tolerances.

This guide provides concrete numbers you can use when designing parts for EOD Cube's manufacturing services.

How do tolerances differ between FDM, SLA, and DLP?

Tolerance is the acceptable deviation between your CAD model and the final printed part. Here's how the three technologies compare:

| Specification | FDM | SLA | DLP | |---|---|---|---| | Dimensional tolerance | ±0.2–0.3mm | ±0.1–0.15mm | ±0.1mm | | Min. layer height | 0.1mm | 0.05mm | 0.05mm | | Min. wall thickness | 1.2mm (recommended) | 0.5mm | 0.5mm | | Min. hole diameter | 1.5mm | 0.5mm | 0.5mm | | Min. embossed text | 0.6mm height, 0.5mm width | 0.3mm height | 0.3mm height | | Min. engraved text | 0.6mm depth, 0.5mm width | 0.3mm depth | 0.3mm depth | | Unsupported overhang | Up to 45° | Up to 30° (needs supports) | Up to 30° (needs supports) | | Max build volume | 300×300×300mm | 192×120×200mm | 192×120×65mm |

What is the minimum wall thickness for each technology?

Wall thickness is one of the most common failure points in 3D printing design.

• FDM: Minimum 0.8mm (2 nozzle widths). Recommended 1.2mm+ for mechanical parts. Walls below 0.8mm will not print reliably and may delaminate under stress.
• SLA/DLP: Minimum 0.5mm for supported walls. Free-standing walls should be 0.8mm+ to survive the washing and curing process without warping.

What hole sizes print accurately?

Small holes are consistently undersized in all 3D printing technologies due to thermal contraction (FDM) or light bleed (resin).

• FDM: Design holes 0.2–0.4mm larger than target diameter. A 5mm hole should be designed as 5.3mm.
• SLA/DLP: Design holes 0.1–0.2mm larger. Light bleed causes slight over-curing at hole edges.
• Press-fit holes: Add 0.1mm interference for FDM, 0.05mm for resin.

What clearances are needed for moving assemblies?

If your design has parts that move relative to each other (hinges, ball joints, sliding fits):

| Fit Type | FDM Clearance | SLA/DLP Clearance | |---|---|---| | Tight / Press fit | 0.1mm | 0.05mm | | Sliding fit | 0.3mm | 0.15mm | | Free rotation | 0.5mm | 0.3mm |

How does part orientation affect accuracy?

In FDM, the Z-axis (vertical) has the coarsest resolution — determined by layer height. The X-Y plane (horizontal) is governed by nozzle diameter and motion system precision, which is generally tighter. This means:

• Circular features (holes, cylinders) should be oriented with their axis perpendicular to the build plate for best roundness.
• Critical dimensions should be placed in the X-Y plane wherever possible.
• Surfaces facing upward (top surfaces) are smoother than downward-facing surfaces (which rest on supports).

For SLA/DLP, resolution is uniform in X-Y (determined by laser spot size or projector pixel pitch) and governed by layer height in Z.

Design checklist for manufacturing

Before uploading your file to EOD Cube's instant quoting engine, verify:

1. Wall thickness ≥ 1.2mm for FDM, ≥ 0.5mm for resin
2. Holes oversized by the compensation values above
3. Clearances between moving parts are sufficient for the technology
4. Text height ≥ 0.6mm for FDM, ≥ 0.3mm for resin
5. File is watertight — no non-manifold edges or inverted normals (our engine will flag these)
6. Overhangs under 45° for FDM; consider adding support points for steep overhangs in resin

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Related guides: Materials Comparison · Cost Guide · Functional vs Display Parts

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