Design Guidelines for SLS 3D Printing

By Sam Gribben
August 22, 2025
6:00 pm

SLS Design Guidelines are essential when creating parts for Selective Laser Sintering, as the approach differs from other methods like SLA or FDM. Factors such as wall thickness, part orientation, and feature design directly influence print quality, strength, and repeatability. At SGD3D, we provide a complete SLS 3D printing service for both prototypes and end-use parts, and applying the right design rules ensures consistent, high-performance results. In this article, we’ll cover the most important SLS design considerations and explain why they matter across industries such as aerospace and medical (see our guide on SLS applications in industry for real-world examples).

Introduction to SLS Design Guidelines

Think 3D printing can print any geometry, especially SLS with complex features? Not all the time, there are DFM (Design for Manufacturing) constraints which must be followed to ensure that results are accurate and repeatable.

Minimum Wall Thickness & Feature Size

3D prints need a minimum wall thickness because of the way materials and processes behave during printing and after cooling. If walls are too thin, they often fail during printing or in use. The main reasons are:

Structural Integrity

Thin walls may not have enough strength to support themselves, especially during overhangs, bridging, or when the part is handled.
They are more prone to warping, cracking, or collapsing.

Printer Limitations

Every 3D printing process (FDM, SLA, SLS, etc.) has a limit on how fine it can consistently produce solid walls.

For example:

FDM is constrained by nozzle diameter (usually 0.4 mm) and extrusion stability.
SLA can produce very thin features but resin curing needs enough cross-section to be stable.
SLS needs enough fused powder to resist breakage when the loose powder is removed.

Post-Processing

Cleaning, de-powdering (SLS), or washing (SLA) can break very thin walls.
Surface finishing like sanding, painting, or vapor smoothing can reduce thickness further, making fragile walls unusable.

Thermal and Shrinkage Stresses

During cooling or curing, parts shrink. If the wall is too thin, the stresses can distort or crack it.

Usability

Even if a printer can technically produce a 0.2 mm wall, the finished part may not survive normal handling or functional use. Minimums ensure parts can actually be used.
Thin walls may not have enough strength to support themselves, especially during overhangs, bridging, or when the part is handled.
They are more prone to warping, cracking, or collapsing.

Recommended Thickness for Nylon PA12 GF (Glass Filled)

For SLS Nylon PA12 GF (glass-filled) the minimum recommended wall thickness is higher than standard PA12 because the glass fibres make the material stiffer but also more brittle.

Here are the usual guidelines:

Minimum Wall Thickness - SLS PA12 GF

Supported walls (connected on 2+ sides): 1.5 mm minimum
Free-standing or load-bearing walls: 2.0–2.5 mm minimum
Thin features (like pins or clips): ≥2.0 mm to avoid snapping during depowdering or handling

Why it's Thicker than Standard Nylon PA12

Standard PA12 can often go down to 0.7–1.0 mm in supported areas.
With glass-filled PA12, the material has less flexibility, so thin walls can fracture rather than bend.
Post-processing (blasting, dyeing, machining) also puts stress on the part, so walls need more bulk to survive.

Extra Recommendations

Add fillets and radii to reduce stress points.
Avoid long, flat unsupported sheets under 2 mm.
For parts under functional load, treat 2.5–3 mm as a safe baseline.

Hollowing and Escape Holes

Holes: Minimum diameter of 1.5 mm.
Internal channels: At least 2 mm to ensure powder can be removed.
Tip: Add escape holes for larger cavities to allow unused powder to flow out.

Tolerances & Dimensional Accuracy

Shrinkage Considerations

Shrinkage needs to be taken into account in SLS (Selective Laser Sintering) 3D printing because the process involves heating powder close to its melting point and then fusing it layer by layer. When the part cools down after sintering, the material naturally contracts, leading to dimensional changes.

Here’s why it matters:

Thermal Contraction of the Material

Nylon powders (like PA12, PA11, PA12 GF) expand when heated by the laser, then contract as they cool.
If this isn’t compensated for in the print setup, the part will be smaller than designed.

Dimensional Accuracy

Shrinkage typically ranges from 2–3% for PA12 and slightly higher for filled materials (like GF or CF).
Without applying shrinkage factors in the build file, parts won’t match CAD dimensions, which is critical for functional components.

Stress and Warping

Uneven shrinkage causes internal stresses. Large, flat, or thin-walled parts can warp, curl, or crack if not designed with this in mind.

Repeatability and Fit

If a part needs to mate with other components (like housings, clips, or assemblies), uncorrected shrinkage can cause misalignment.
Manufacturers apply compensation factors (scaling in the x, y, z directions) so finished parts meet tolerance requirements.

Designing for Assemblies

When you’re designing parts that will be assembled after SLS 3D printing, you need to account for both the process characteristics and the material behaviour. Here are the key considerations.

Tolerances and Clearances:

Shrinkage & Accuracy: SLS typically has a dimensional tolerance of ±0.3 mm + 0.3% of dimension.
Assembly Fit: Allow clearance between mating parts:
- Sliding fits: 0.2 – 0.5 mm gap
- Snug press fits: 0.1 – 0.2 mm interference
- Loose functional assemblies: ≥0.5 mm gap
Always test with prototypes to dial in fits for your machine and material.

Wall Thickness:

Maintain recommended wall thicknesses (≥1 mm for PA12, ≥2 mm for PA12 GF) so parts don’t crack under assembly stress.
Add fillets or chamfers to reduce stress concentrations where parts join.

Alignment Features:

Use locating pins, slots, or tabs for easy alignment.
Keep features robust (≥2 mm thick/diameter) to avoid breaking during depowdering or assembly.
Chamfer edges for easier insertion.

Fastening Methods:

Snap-fits: Possible, but design thicker and more flexible beams in PA12. PA12 GF requires additional vapour smoothing to improve flexural modulus.
Threads: Use inserts (heat-set brass inserts) instead of printing fine threads. If printing, use coarse threads only.
Adhesives: SLS nylon bonds well with cyanoacrylate or epoxy for permanent assemblies.

Post-Processing Effects:

Dyeing, vapor smoothing, or painting can add thickness (0.05 – 0.2 mm). Factor this into clearance for tight assemblies
Surface blasting slightly reduces material from sharp edges, altering fits.

Moving Assemblies (Print-in-Place):

If you’re printing hinges, chains, or gears already assembled:

Maintain a minimum 0.5 mm gap between moving surfaces
Increase to 0.7 – 0.8 mm for large or complex parts to ensure powder removal.

Part Orientation & Build Volume

Dimensional Accuracy & Shrinkage Compensation:

Parts can shrink differently along the X, Y, and Z axes
Orienting a part to minimise shrinkage distortion helps maintain tolerances.

Surface Finish:

Horizontal (XY plane) surfaces are usually smoother, while vertical (Z axis) surfaces can show more stepping.
Orienting cosmetic faces flat reduces visible layer stepping.

Mechanical Properties:

SLS parts are anisotropic (stronger in X-Y plane than Z axis).
If a part needs strength in a specific direction, orient it so the load-bearing features align with the stronger axes.

Powder Removal & Print Success:

Hollow parts or intricate designs need to be oriented so that unfused powder can be removed.
Poor orientation can trap powder, leading to rejected parts.

Packing Efficiency:

Better orientation allows more parts to be nested into one build, reducing costs per part and improving turnaround.

Post-Processing Considerations

Surface Finish Requirements

We offer a number of different post-processing solutions available for SLS which include:

Vapour Smoothing
Cerakote Ceramic Coating
Spray Painting (1k / 2k Finish)
Dying

Industries That Require Design Precision

Selective Laser Sintering (SLS) is widely used across industries where dimensional accuracy, repeatability, and tight tolerances are critical. In these sectors, even small deviations can compromise performance, safety, or regulatory compliance.

Automotive and Aerospace:

Both industries rely on SLS for lightweight components, prototypes, and functional end-use parts. Tight tolerances are essential for parts that must integrate seamlessly with existing assemblies, such as brackets, housings, and interior fittings.

Medical and Healthcare:

From surgical guides to prosthetics and orthotics, SLS is valued for its ability to produce customised solutions with reliable accuracy. Design precision ensures patient-specific devices fit correctly and function as intended.

Industrial Manufacturing:

SLS supports the production of tooling, jigs, and fixtures, where exact dimensions are required to maintain process efficiency. Inaccurate parts could lead to costly downtime or defective products on the production line.

Consumer Products:

For applications such as wearables, sports equipment, or product casings, precision ensures both functionality and a high-quality user experience. Consistency in design allows manufacturers to move smoothly from prototype to mass production.

Applying the right design guidelines for SLS 3D printing is the key to achieving accuracy, strength, and repeatability in your parts. Ready to put these principles into practice? Get an instant SLS 3D printing quote from SGD 3D today and see how we can help turn your designs into production-ready components.

3D printing design tips, additive manufacturing design, Industrial 3D printing, nylon 3D printing, powder bed fusion, selective laser sintering, SLS 3D Printing, SLS 3D printing design guidelines, SLS accuracy, SLS design rules

How Nottingham’s Education and Research Sector is Using 3D Printing for Innovation

30Aug

Design Guidelines for SLS 3D Printing

Introduction to SLS Design Guidelines

Minimum Wall Thickness & Feature Size

Structural Integrity

Printer Limitations

Post-Processing

Thermal and Shrinkage Stresses

Usability

Recommended Thickness for Nylon PA12 GF (Glass Filled)

Minimum Wall Thickness - SLS PA12 GF

Why it's Thicker than Standard Nylon PA12

Extra Recommendations

Hollowing and Escape Holes

Tolerances & Dimensional Accuracy

Shrinkage Considerations

Thermal Contraction of the Material

Dimensional Accuracy

Stress and Warping

Repeatability and Fit

Designing for Assemblies

Tolerances and Clearances:

Wall Thickness:

Alignment Features:

Fastening Methods:

Post-Processing Effects:

Moving Assemblies (Print-in-Place):

Part Orientation & Build Volume

Dimensional Accuracy & Shrinkage Compensation:

Surface Finish:

Mechanical Properties:

Powder Removal & Print Success:

Packing Efficiency:

Post-Processing Considerations

Surface Finish Requirements

Industries That Require Design Precision

Automotive and Aerospace:

Medical and Healthcare:

Industrial Manufacturing:

Consumer Products:

Related Articles

How Nottingham’s Education and Research Sector is Using 3D Printing for Innovation

Design Guidelines for SLS 3D Printing

How Birmingham’s Automotive Industry is Using 3D Printing for Faster Production