Updated 2025

3D printing materials and design guide

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 and SLS 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.

Section 1

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

Supported vs. Unsupported Walls

Section 3

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.

The 45-Degree Rule

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 (Horizontal Spans)

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

  Unlimited

  Powder provides support

Design Tips to Minimize Supports

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

Section 5

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.

Accepted File Formats

• 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

STL Export Best Practices

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.

Section 7

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

  Walls too thin

  Most common issue. Review minimum thicknesses per technology.

• Important

  No draft angles on snap-fits

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

• Critical

  Ignoring build orientation

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

• Important

  Sharp internal corners

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

• Critical

  Forgetting escape holes

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

• Common

  Over-engineering details

  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 $75/hour.