Updated 2025

3D printing design guidelines

Complete Guide to Wall Thickness, Tolerances, Overhangs & File Preparation

Designing for 3D printing requires understanding the unique capabilities and constraints of additive manufacturing. This guide covers the essential design rules for FDM, SLA, SLS, and MJF technologies—the same guidelines our engineering team uses to review every order at AllPrototype.

Design rules

Complete specifications for all technologies

Tolerances

Dimensional accuracy for each process

File prep

Export settings and best practices

Pro Tip: Following these guidelines before submitting your files can reduce quote turnaround time by 50% and eliminate costly design revisions.

Wall thickness: the foundation of printable parts

Wall thickness is the single most critical design parameter in 3D printing. Walls that are too thin will fail during printing or break during handling. Walls that are too thick waste material, increase cost, and can cause internal stresses or warping.

FDM/FFF

Minimum

0.8 mm

Recommended

1.2–2.0 mm

2× nozzle diameter

SLA/DLP

Minimum

0.5 mm

Recommended

1.0–1.5 mm

Resin brittleness factor

SLS (nylon)

Minimum

0.7 mm

Recommended

1.0–1.5 mm

Self-supporting

MJF (HP)

Minimum

0.5 mm

Recommended

1.0 mm

Best detail resolution

Supported walls

Connect to other geometry on 2+ sides. These can be thinner because adjacent structures provide reinforcement.

Unsupported walls

Fins, tabs, single-sided features need 20–50% extra thickness to prevent warping and breakage.

Dimensional tolerances & accuracy

Every 3D printing technology has inherent dimensional variability. Understanding these tolerances is critical for parts that must fit together or interface with other components.

FDM

Typical Tolerance

± 0.3–0.5 mm

Layer Height

100–300 μm

Functional prototypes

SLA

Typical Tolerance

± 0.1–0.2 mm

Layer Height

25–100 μm

High-detail models

SLS

Typical Tolerance

± 0.2–0.3 mm

Layer Height

100–120 μm

Functional end-use

MJF

Typical Tolerance

± 0.2 mm

Layer Height

80 μm

Production parts

When designing parts that fit together (snap-fits, assemblies, hinges), add clearance to account for manufacturing tolerances:

Loose fit

0.3–0.5 mm per side

Easy assembly/disassembly

Snug fit

0.15–0.25 mm per side

Friction fit

Press fit

0.05–0.1 mm interference

Requires post-processing

Overhangs, bridges & support structures

3D printing builds layers on top of previous layers. Features that extend outward without support underneath are called overhangs. Understanding overhang limits helps you design self-supporting parts that print faster and cost less.

For FDM and SLA printing, overhangs up to 45° from vertical can typically print without support. Beyond 45°, supports are usually required to prevent drooping and print failures.

0–45°

Self-supporting

No supports needed

45–60°

May print without supports

Degraded quality possible

60–90°

Requires support

Support structures necessary

Bridges are horizontal features that span between two vertical supports. Bridge length limits vary by technology:

FDM

Up to 10 mm

Material dependent

SLA

Up to 20 mm

With proper orientation

SLS/MJF

Unlimited

Powder provides support

1

Add fillets and chamfers to transition overhanging features gradually (45° chamfer instead of 90° overhang)

2

Orient parts strategically — rotating a part 45° can eliminate supports entirely

3

Use teardrop shapes for horizontal holes (pointed at top) to avoid internal supports

4

Consider splitting complex parts and assembling post-print if supports would be excessive

Holes, threads & small features

Small holes tend to close up during printing due to material shrinkage and layer adhesion. Account for this in your design to ensure proper functionality.

Technology	Min Vertical Hole	Min Horizontal Hole
FDM	2.0 mm	3.0 mm (use teardrop)
SLA	0.5 mm	1.0 mm
SLS/MJF	1.0 mm	1.5 mm (add drain holes)

Printing functional threads is possible but comes with limitations:

1

Minimum printable thread: M6 (smaller threads should be tapped post-print)

2

Undersize screw holes by 0.2–0.4 mm to allow for self-tapping

3

For repeated use, install heat-set brass inserts (design hole diameter per insert specs)

File preparation & export settings

A well-prepared file eliminates delays and ensures accurate quoting. Follow these guidelines when exporting your CAD model for 3D printing.

STL

Universal standard, accepted everywhere

STEP/STP

Preferred for dimensional accuracy (native CAD geometry)

3mf

Modern format with color/material data

OBJ

Common for visual models and scans

1

Set resolution/deviation to 0.01–0.02 mm for smooth curves without excessive file size

2

Export in millimeters (mm) — the industry standard for 3D printing

3

Ensure the model is watertight (no holes, non-manifold edges, or inverted normals)

4

Remove internal geometry that won’t be visible (reduces file size and processing time)

5

Check for intersecting bodies — Boolean union all components before export

Pro tip:

Use free tools like Microsoft 3D Builder or Meshmixer to repair STL files before submitting. These can automatically fix non-manifold edges and small holes.

Choosing the right technology

Different 3D printing technologies excel at different applications. Here’s a quick decision guide to help you choose the best process for your needs.

Need	FDM	SLA	SLS	MJF
Lowest cost	★ ★ ★	★ ★ ★	★ ★ ★	★ ★ ★
Fine detail	★ ★ ★	★ ★ ★ ★	★ ★ ★	★ ★ ★
Strength	★ ★ ★	★ ★ ★	★ ★ ★	★ ★ ★
Large parts	★ ★ ★	★ ★ ★	★ ★ ★	★ ★ ★
Production qty	★ ★ ★	★ ★ ★	★ ★ ★	★ ★ ★

Not sure which technology to choose? Our team can help you select the best process for your application. Contact us for a free consultation.

Common design mistakes to avoid

Learn from the most frequent design issues we encounter. Avoiding these mistakes will save you time, money, and ensure your parts print successfully on the first attempt.

Critical

Most common issue. Review minimum thicknesses per technology.

Important

Vertical walls bind; add 1–2° draft for easy assembly.

Critical

Layer lines affect strength (parts are weakest between layers).

Important

Add fillets (≥0.5 mm radius) to reduce stress concentrations.

Critical

Hollow SLA/SLS parts need ≥3 mm drain holes for uncured resin/powder.

Common

Text under 6pt and features under 0.5 mm won’t resolve clearly.

Important note

Our engineering team reviews every order before production. If your design needs adjustments, we'll let you know exactly what to change—or we can modify it for you at $80/hour.

Pre-submission checklist

Before uploading your file, verify these items to ensure a smooth manufacturing process and avoid costly delays or revisions.

All walls meet minimum thickness requirements

Clearances added for mating/moving parts

Model is watertight (no holes or non-manifold geometry)

File exported in mm at appropriate resolution

Escape holes added for hollow parts (SLA/SLS)

Overhangs reviewed for support requirements

Critical dimensions noted for inspection

Free design review

Upload your file and we’ll check it against these guidelines at no charge.

Design assistance

Need help optimizing your part for 3D printing? Our CAD team is available at $80/hour.

Get a quote

Ready to get started? Upload your files for an instant quote.

Fast response

Need help with your design?

Our engineering team reviews every order before production. If your design needs adjustments, we’ll let you know exactly what to change—or we can modify it for you.

Free design review

Upload your file and we’ll check it against these guidelines at no charge.

Design assistance

Need help optimizing your part for 3D printing? Our CAD team is available at $80/hour.

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3D printing design guidelines

Design rules

Tolerances

File prep

Wall thickness: the foundation of printable parts

0.8 mm

1.2–2.0 mm

0.5 mm

1.0–1.5 mm

0.7 mm

1.0–1.5 mm

0.5 mm

1.0 mm

Supported walls

Unsupported walls

Dimensional tolerances & accuracy

± 0.3–0.5 mm

100–300 μm

± 0.1–0.2 mm

25–100 μm

± 0.2–0.3 mm

100–120 μm

± 0.2 mm

80 μm

Overhangs, bridges & support structures

0–45°

Self-supporting

45–60°

May print without supports

60–90°

Requires support

Up to 10 mm

Up to 20 mm

Unlimited

1

2

3

4

Holes, threads & small features

1

2

3

File preparation & export settings

STL

STEP/STP

3mf

OBJ

1

2

3

4

5

Pro tip:

Choosing the right technology

Common design mistakes to avoid

Important note

Pre-submission checklist

Need help with your design?

Free design review