SLS 3D Printing · Reference
Design Guidelines & File Requirements
What a printable file looks like. The ordering app links here when a model fails or warns on automated checks.
Accepted files
| Item | Requirement |
|---|---|
| Format | STL today, one part per file. OBJ and 3MF are on the roadmap. |
| Units | Millimeters. A file exported in inches or meters arrives at the wrong size. |
| Max file size | 100 MB per file. |
| One part per file | Each file holds a single part. For several parts, upload several files. |
| Files per order | Up to 50 files per order. Each file is checked and priced on its own. |
Build envelope
Models must fit the printer's printable maximum of 159.8 × 159.8 × 295.5 mm (the part can be turned to fit; the checks try every axis order).
Tip Parts larger than the envelope can sometimes be split and joined. That is consultation work, not a print-product service.
SLS design rules
| Rule | Why |
|---|---|
| Walls at least 0.6 mm thick (0.3 mm for horizontal walls) | Thinner walls warp, detach, or break during powder removal. |
| Hollow parts need at least two escape holes, 3.5 mm or larger | A sealed hollow stays full of powder and is rejected by the checks. Lattices need gaps of 8 mm or more for the same reason. |
| Parts printed as one moving assembly need 0.6 mm of clearance (0.3 mm for features under 20 mm²) | Surfaces closer than that sinter together. Parts assembled after printing need 0.4 mm (0.2 mm for small features). |
| Fine features: pins at least 0.8 mm across, holes at least 1.0 mm, embossed text at least 4.5 mm tall and engraved text 3 mm, in a bold face | Thinner pins snap during powder removal, smaller holes close up, and small text does not show. |
Residual powder SLS parts can hold a little loose powder after cleaning, especially in narrow openings, internal channels, and cavities. We do not guarantee complete powder removal from features our cleaning tools cannot reach. Formlabs describes the cleaning process.
Mesh repair
Small mesh defects (under half a percent of a file's edges) are repaired automatically by our printer software once you acknowledge it on the quote page; files with more defects than that are refused, not repaired.
Repair can change the geometry of a part. It is not a design review, and the Studio is not responsible for changes a repair introduces. When in doubt, re-export or repair the mesh in your own modeling tool before uploading, so you control the result.
Designing for SLS
New to selective laser sintering? Formlabs publishes design guidance for the Fuse series and for Nylon 12 that applies directly to what we print:
Orientation
We choose how parts sit in the build. On the Fuse, orientation changes surface finish (downward-facing surfaces come out smoother, upward-facing ones crisper), the accuracy of holes and pins (best with their axis vertical), and how many parts fit in a build. We pack each build for reliable prints and efficient use of powder.
If a particular face or feature matters to you, say so in the notes on your order. We follow requests when they do not put the print at risk, but we do not guarantee a requested orientation. An STL file carries no orientation, so the file itself is not a request.
What the automated checks do
The checks identify problems: they do not fix files and do not judge fitness-for-purpose. A passing check means the part can be printed safely, not that it will do what you intend.