Most 3D printing failures do not happen on the printer. They happen in the CAD file. A part with too-thin walls, an unclosed mesh, or a bad orientation will fail no matter which printer you send it to. Preparing your STL file correctly is the single highest-leverage thing you can do to get a part you are happy with on the first print.

This guide walks through the file prep that our in-house engineers perform on every incoming order — so you know what to check before you upload.

Start with the right export settings

Most 3D printing services accept STL, STEP, and 3MF files. When you export, check these settings:

  • Units. STL files do not carry units — a 1000-unit part could be millimeters (normal) or meters (comically oversized) or inches (extremely tiny). Always confirm the unit when you upload, and use a tool that previews the part at scale.
  • Mesh resolution. Most CAD exporters let you set the deviation (chord height) and angle. For functional parts, use 0.01mm chord height and 1° angle. Lower is better but files get huge. Higher resolution creates a smoother surface but does not affect the print itself for FDM parts.
  • Binary vs ASCII STL. Always use binary. ASCII STL files are 5–10x larger with no benefit.
  • STEP for curved geometry. If your part has precise curves or tight tolerances, send STEP instead of STL. STEP is the parametric original — no mesh approximation.

Check wall thickness

Every 3D printing technology has a minimum wall thickness it can actually print. If your walls are thinner than the minimum, they either fail to print at all or come out so fragile they break on removal from the build plate.

General minimums:

  • FDM: 1.0–1.2 mm (two perimeters)
  • SLA: 0.6 mm for load-bearing, 0.4 mm for cosmetic-only
  • MJF: 0.8 mm for load-bearing, 0.5 mm for cosmetic-only
  • Industrial SLA: 1.0 mm
Thin walls fail in specific ways: FDM walls deform during printing, SLA walls crack during cleaning, MJF walls break during powder removal. If you are not sure whether a wall is thick enough, use the wall-thickness analysis tool in your CAD software.

Think about orientation before you print

Orientation affects cost, strength, and surface finish — often more than the technology choice itself.

  • Strength. FDM parts are anisotropic — they are weakest along the Z-axis (the print direction). If your part has a load path, orient it so the load travels along the XY plane, not through layer lines.
  • Surface finish. Down-facing surfaces in SLA are rougher because of support marks. Orient cosmetic surfaces facing up if possible.
  • Supports. The more supports a part needs, the more expensive it is and the more cleanup it requires. Tall thin parts printed vertically need fewer supports than flat parts printed horizontally.
  • Build time. Orientation affects print height, which is the primary driver of FDM print time.
We usually pick orientation for you based on the best trade-off for your part. If you want specific orientation locked in, tell us in the order notes.

Close the mesh

An STL file is a collection of triangles that should form a closed watertight surface. When the mesh has holes, non-manifold edges, or inverted normals, slicers either refuse to slice the part or slice it incorrectly.

The fastest way to check your mesh is to open the file in Netfabb, Meshmixer, or the free Microsoft 3D Builder app. Each of these will tell you if the file is watertight and offer a one-click repair. For complex issues, the free online service of Netfabb is surprisingly capable — upload a broken STL and download a fixed one in seconds.

We run every incoming file through a mesh check before it prints. If we find issues, we either fix them ourselves or email you to confirm before proceeding.

Design for the technology

Each 3D printing process has quirks you can design around to get dramatically better parts:

FDM

  • Add fillets (0.4–1mm) to vertical corners to reduce stress concentrations at layer lines
  • Avoid horizontal holes larger than 10mm — they print as ellipses. Reorient or drill after printing.
  • Use 45° chamfers instead of 90° overhangs to avoid support material

SLA

  • Orient cosmetic surfaces facing up
  • Avoid large flat downfaces — they need heavy supports and leave witness marks
  • Add drainage holes to hollow parts so resin can escape
  • Design for support removal — leave clearance around delicate features

MJF

  • Leave 0.5mm clearance for moving parts and assemblies
  • Add escape holes to hollow cavities so un-fused powder can be removed
  • Avoid feature walls thinner than 0.8mm in functional areas

Upload and order

Once your file is prepped, upload it to our quoter. The system analyzes geometry in real time and flags any manufacturability issues before you place the order. If our engineers spot something during our human review, we email you before printing — every time, no exceptions.