The rules below are the reference values Formlabs publishes for the Fuse printers, measured on PA12. They are minimum values. At these sizes a feature still forms correctly, which does not guarantee that it will withstand the load in your application. For PA11, TPU 90A and polypropylene, Formlabs gives slightly larger minimum features that also vary with part orientation, so with these materials leave a margin or ask for a test print.
SLS does not use supports, so the FDM and SLA rules about overhangs, 45° angles and support faces do not apply here. What matters instead is how the part cools and how you get the powder out of it. Uniform walls, escape holes for cavities and the right clearance between moving parts solve most problems before they appear. If a feature is borderline, the cheapest option is to print a small test piece in the same orientation as the real part.
0.6 mm
Minimum wall thickness
Use 0.6 mm for vertical walls and 0.3 mm for horizontal walls, whether the wall is attached along 1 edge or several. Thinner walls can warp or break away. This value only ensures that the wall forms. For parts that are handled often or carry a load, size the wall for the load it takes.
1.0 mm
Minimum hole diameter
Holes under 1 mm can close up during printing. Holes are most accurate when their axis is vertical (Z) in the chamber. For precise concentric holes, design a pilot hole slightly undersize and ream it to size.
0.8 mm
Minimum pin diameter
This is the smallest pin or rod diameter that prints correctly. Thin pins can break during cleaning, so add a fillet radius at the base. For precise location, use pressed-in metal dowel pins instead of printed ones.
2 × 3.5 mm
Escape holes for hollow parts
A closed cavity stays full of unsintered powder. Add at least 2 escape holes with a diameter of at least 3.5 mm; more holes and larger holes make cleaning easier. In PA12 GF the inner surface is harder to clean, so the holes need to be larger, preferably with direct access to all inner faces.
0.3 / 0.6 mm
Clearance for parts printed already assembled
For parts that print together and have to move, such as hinges, joints and mechanisms, use 0.3 mm on features under 20 mm² and 0.6 mm on features over 20 mm². In PA11 and TPU 90A start from at least 1 mm and adjust after a test print.
0.2 / 0.4 mm
Clearance for parts assembled after printing
For parts printed separately that fit together, such as lids, joints and gears, use 0.2 mm on features under 20 mm² and 0.4 mm on larger ones. Mating parts should be oriented the same way in the chamber so that they fit.
4.5 / 3 mm
Embossed and engraved text
Embossed text needs a character height of at least 4.5 mm and 0.3 mm of relief. Engraved text needs a character height of at least 3 mm and a depth of 0.3 mm. For details other than text, the minimum is 0.15 mm embossed and 0.1 mm engraved on horizontal faces. Use a bold font.
±0.3 mm / ±0.5%
Dimensional tolerances
On X and Y the tolerance is ±0.5% or ±0.3 mm, whichever is greater. On Z, the build axis, Formlabs gives ±1% or 0.6 mm, so treat height as less accurate. These values are measured on PA12. Mark critical dimensions in your request and allow for reaming or bushings on tight fits.
≥ M6
Printed threads and inserts
Printed threads are workable from M6 upwards and for parts you assemble rarely. For screws that are tightened often or carry a load, use heat-set brass threaded inserts. Self-tapping screws for plastics work well in PA12 and PA11.
~20°
Flat and wide parts
SLS does not use supports, so there is no overhang limit. The real problem comes during cooling, when large flat plates and parts with very uneven wall thickness can warp. Formlabs recommends orienting wide, flat parts at about 20°, keeping wall thickness uniform and adding ribs or fillets to long, thin sections. PA11, TPU 90A and PP warp more easily than PA12.
XY > Z
Part orientation
Parts are tougher in the XY plane than along Z, so features that flex, such as clips and hinges, should work in XY. Holes and pins are more accurate with their axis along Z. Rounded faces that need to come out smooth should face downwards, and faces with sharp edges should face upwards. We choose the orientation, so if you have requirements, write them in your request.
≥ 8 mm
Lattice structures
The powder has to be able to get out of the structure. Leave openings of at least 8 mm between lattice members and leave faces open, so that no powder stays trapped inside.
Sources
- Formlabs, Fuse Series SLS Design Guide (March 2023)
- Formlabs, Measuring SLS Dimensional Accuracy and Print Repeatability
- Formlabs, 3D Printing Threads and Adding Threaded Inserts to 3D Printed Parts
Not sure your part follows the rules? Send the file through the quote form and we'll tell you what needs changing before printing. For choosing the file, see also how to prepare your STL or STEP file.