SLA and Resin Printing#

Overview#

Stereolithography (SLA), digital light processing (DLP) and masked SLA (MSLA, the technology in most low-cost "resin printers") all cure liquid photopolymer with light. The part is built layer by layer, either hanging from a plate that rises out of a vat, or on a platform in a vat that moves down. Layer heights of 0.025-0.1 mm and in-plane features of 0.05-0.15 mm are routine, so resin gives much finer detail and smoother surfaces than FDM. In exchange you handle liquid resin, must wash and cure parts, and design for different failure modes: suction forces, trapped liquid, peel stress and cure shrinkage.

Fusion designs for resin are ordinary solid bodies exported to STL or 3MF. The resin-specific work happens in your design (hollowing and drain holes, minimum features) and in the resin slicer (orientation, supports, exposure). Fusion's Manufacture workspace also supports SLA/DLP additive setups: you pick an SLA/DLP machine and print setting, position the parts, add supports (volume, bar or polyline; some need the Fusion Manufacturing Extension) and generate a 3MF or machine-specific file (Autodesk's tutorial covers an SLA setup). Many users still prefer the resin manufacturer's slicer. The layer-height and feature-size figures on this page are general industry guidance, not Autodesk data.

Where to find it#

Step by step#

Designing a resin-friendly part#

1. Decide whether to hollow. Solid resin parts use a lot of expensive resin, suffer more shrinkage stress, and can crack or warp. For anything larger than roughly 20-30 mm, consider hollowing.
2. Hollow with Shell. Select the body, run Shell, choose a thickness (typically 1.5-3 mm for small parts, more for large), and click the face(s) to remove or leave the body closed. For a closed hollow, Fusion's Shell can produce an internal void if no face is removed (verify in your version).
3. Add at least two drain holes. Resin trapped in a closed cavity cannot drain and may later burst during curing or heat. Two holes allow air in while resin flows out. Each hole should be 3-5 mm in diameter for typical resin viscosity (use larger for thick resin), placed at the lowest point and the highest point of the cavity in the print orientation, and ideally on a hidden face.
4. Plug the holes later or keep them as part of the design, such as screw holes or cable passages. Some users plug with cured resin or filler after washing.
5. Keep minimum features above the resolution. Typical safe minimums for MSLA: wall 0.8-1.0 mm (0.5 mm for tiny fragile details), supported pin 0.5-0.8 mm, embossed detail 0.2-0.3 mm, engraved detail 0.3-0.5 mm wide and deep.
6. Avoid large flat horizontal faces facing the build plate because they create strong suction and peel forces. Tilt the model in the slicer 15-45 degrees.
7. Avoid cups. A cup is any concave shape that opens downward and can trap resin or air; each one is a suction pocket and a likely failure. Add a drain/vent hole at the highest point in the print orientation, or reorient so the opening faces sideways or up.

Orientation and supports for resin#

1. Tilt, do not lay flat. A tilt of around 30-45 degrees reduces layer cross-section area, which reduces peel force and improves surface quality.
2. Hide the support-scarred surface. Supports leave small marks; put the cosmetic face away from the supports.
3. Use many small supports (light touch points 0.3-0.5 mm) rather than a few big ones, and give extra supports at islands: points that appear in a layer with nothing below them.
4. Raise the part off the plate by a few millimeters with a raft so the first layers have room.
5. Check for trapped volumes in the slicer's preview. Cups that are not drained or vented will fail.

Post-processing#

1. Drain excess resin from the part by holding it over the vat or using a drain time before removal.
2. Wash in isopropyl alcohol (or water-washable resin water), by agitation or an ultrasonic bath, for the time recommended by the resin manufacturer. Do not over-wash; some resins soften and develop cracks.
3. Remove supports before final cure for most resins (the part is still slightly soft and cuts cleanly), or after for brittle resins; follow the resin guidance.
4. Post-cure with UV light for the recommended time and temperature. This sets final strength and dimensions.
5. Sand and prime as needed. Resin takes paint very well.

Options reference#

Tips and pitfalls#

Tip: Make the drain holes a design feature, not an afterthought. In Fusion, place them with a Hole or Extrude Cut so they stay parametric and can be repositioned if you reorient the part.

Warning: Closed hollow cavities with no holes are dangerous in resin printing: trapped liquid expands and cracks the part during UV curing, and it can leak out later. Always provide at least two holes.

Tip: If you are printing gears, threads or press-fit parts, print a test strip with different clearances in your specific resin and curing process, because resins differ widely in shrinkage.

Warning: Resin is a skin sensitizer. Wear nitrile gloves, work in a ventilated area, and follow the manufacturer's safety data sheet for handling, curing and disposal. Do not pour uncured resin down the sink.

Warning: Large flat parts can warp during post-cure. Cure them in the supported orientation or on a flat fixture, and avoid long, thin, unsupported spans.

Tip: For tiny, delicate models, increase the thickness of fragile details by 10-20 percent in Fusion (use Offset Face under Modify > Press Pull) to survive handling, then sand the excess.

Tip: Use high mesh quality when exporting organic or curved shapes. Resin's fine layers reveal faceting that FDM hides. A surface deviation of 0.01-0.02 mm is not unusual. See the exporting page.

Design patterns that work well in resin#

Snap-fits are less forgiving than in nylon because standard resins are brittle. Use tough or flexible resins, thicker roots, and generous fillets, and expect small parts to break at first.

Lattices and perforations reduce weight and resin consumption. Model with the pattern commands (Rectangular or Circular Pattern) and keep strut thickness above 0.8 mm.

Threads print well at M3 or larger, but expect to chase them with a tap. Orient the thread axis vertical or at a slight tilt, never horizontal.

Jewelry and dental-type parts have specialized casting or biocompatible resins with their own geometry limits. Follow those materials' guidelines and any applicable regulations; this guide does not cover them.

Enclosures benefit from internal ribs rather than thick walls. Resin parts shrink slightly while curing, so the bosses and clips should have fillets and uniform wall thickness.

Practice exercise#

Model a 50 mm tall desk figurine or any organic solid body. Duplicate it, then hollow the duplicate with Shell at 2 mm. Add two 4 mm drain holes at the base and the back-top, hidden where possible. Compare the Properties volume of each version (right-click body > Properties). Expected result: the hollow version uses perhaps 60-80 percent less material. Export both to your resin slicer, tilt them 30 degrees, auto-support, and compare estimated resin volumes and support counts. Confirm the slicer shows no trapped volumes on the hollow version.

Related#

• Preparing Models for Printing
• Orientation and Support Generation
• Exporting STL and 3MF
• Shell, draft and scale (03-solid-modeling)

Understanding resin failure modes#

Resin prints fail for reasons that have no equivalent in FDM, so it pays to know the mechanisms. Each one points to a specific design or preparation response in Fusion.

Peel force. After each layer cures, it is stuck to the bottom of the vat's film and must be peeled free. The force scales with the cross-sectional area of the layer. A large flat horizontal face produces a huge sudden area change and a strong peel, which can pull the part off its supports or off the plate. Tilting the model reduces the area per layer, and hollowing reduces the area of cured plastic in each layer. If a design has a big flat face by necessity, split it into two bodies that print separately and bond afterward.

Suction. A downward-facing cup pulls resin in as it rises, creating vacuum. This can tear thin walls or leave voids. The fix is a vent hole at the highest point of the cup in the print orientation. Model the hole in Fusion, because it then travels with the design.

Island layers. When a section of the part first appears at a layer height where there is nothing beneath it (such as the tip of a raised arm), it floats and drifts unless supported. The slicer's island detection highlights these; you either add supports or re-orient. In design, soften pointy downward-facing tips with fillets.

Cure shrinkage and warp. Resin shrinks as it polymerizes, typically a fraction of a percent to a few percent, and does so nonuniformly. Long thin parts bow; large flat parts curl. Consistent wall thickness, ribs and orientation minimize it. If you need tolerances tighter than around 0.1-0.2 mm, calibrate with a test and offset the critical features in the model using parameters.

Brittleness and creep. Standard resins are brittle, and some soften or creep under sustained load or heat. Pick the resin for the job (tough, flexible, high-temperature, castable) and do not design snap-fits or living hinges in a brittle resin without testing.

Choosing between resin and FDM for a Fusion design#

Use resin when surface finish, tiny features or near-isotropic strength matter: miniatures, jewelry masters, small functional prototypes with fine threads, and master patterns for silicone molding. Use FDM when size, cost, toughness or engineering filaments matter. A good hybrid is to print a large structure in FDM and fine-detail components in resin, with alignment pins and clearance holes designed in one Fusion assembly, so a single parameter change updates both.

Resin-specific export advice#

Export at higher mesh quality than for FDM, because small facets show on a smooth surface. When you hollow in Fusion with Shell, the exported mesh includes the inner surface, which doubles the triangle count. If you prefer, leave the model solid and use the slicer's hollow tool with drain holes, which is quicker to iterate on but does not travel with the model. Whichever method you choose, record it in your notes so a colleague opening the file does not hollow it twice. Also record the resin name and post-cure settings used for any dimensionally critical part, since the same model printed in a different resin can differ by tenths of a millimeter.