Resin Orientation and Supports

Orientation and supports for resin follow different rules from FDM, because the part hangs upside down from the build plate and is pulled off the film once per layer. Print Orientation and Supports and Overhangs cover the shared ideas; this lesson covers what is specific to resin.

The force on every layer

After each layer cures against the film, the printer lifts the part away. Formlabs describes this as the force of lifting the part away from the tank film after each layer, and it is strong enough to pull a part off its touchpoints. Three things make it worse:

• Large or suddenly growing layer area. Formlabs' advice is to minimize each layer's XY cross-section and to minimize the change in area between layers; a sudden increase in area causes shrinkage defects and curling.
• Suction cups. A cavity whose open side faces the film traps resin and air between the part and the tank and creates suction (Formlabs). Bowls, cups, the inside of hollow models and concave surfaces are the usual cases.
• Shrinkage. Formlabs notes that each new layer imparts a force on the part as it shrinks, and the buildup can warp a part or break it free of its supports.

Orientation: tilt, and keep layers changing slowly

• Tilt flat parts. A flat plate printed parallel to the screen has its whole area peeled at once. Formlabs suggests tilting to about 45 degrees Rule of thumb to reduce the change between layers, and setting large flat surfaces at a shallow angle to the build platform rather than parallel to it.
• Long parts vertical. Formlabs recommends orienting along the longest dimension vertically to keep each layer small.
• Turn cups away. Orient so cavities do not open toward the film, or add drainage holes (see Hollowing). For symmetric shapes like cones, Formlabs suggests tilting so the shape does not expand symmetrically layer after layer.
• Keep good faces away from supports. Supports go on the side of the model that faces the build platform, and every touchpoint leaves a mark. Formlabs advises orienting cosmetic, detailed and mating surfaces away from the supports.
• Think about fit. Formlabs warns orientation affects the final fit of interlocking parts.

Self-supporting angles: Formlabs says stiff, rigid materials can self-support when the surface is more than 45 degrees from horizontal; Carbon says 40 degrees or more is most common Rule of thumb. Treat both as starting points that depend on the resin.

Islands

Carbon defines an island as a feature that begins printing above the platform before it is connected to the rest of the part: the tip of a hanging arm, the lowest point of a chin, the bottom of a loop. Formlabs uses the word "minima" for the same thing. An island has nothing above it to hang from when its first layer cures, so it must have a support at that exact point.

• Reorient to remove islands. Carbon and Formlabs both suggest it first. Formlabs adds that branching features should build off a common base rather than merge from separate starts.
• Let the slicer find them, then check. In PrusaSlicer, automatic supports place one point at the center of mass of a small island, two or more on a medium island, and points along the axis or perimeter of a large one; islands show in blue. That is how Prusa's current documentation describes PrusaSlicer. Other slicers have their own island detection; check their documentation.
• Step through the layers. Whatever your slicer reports, scrub the layer preview and look for any new separate area that has no support under it.

Support density and size

Supports have to hold the part against the peel force, layer after layer. Too few, and the spans between them flex. Formlabs calls the resulting droop "bat-winging" and says it is caused by insufficient support density; the fix is to orient the part more vertically or increase density, with touchpoints spaced evenly.

• Start with the slicer's default density Starting point. Prusa says the standard value should be good for most cases, and its density slider updates the preview as you move it.
• Heavier parts need thicker supports. For a stronger support set in PrusaSlicer, Prusa suggests a support head front diameter of 0.6 mm, support head penetration of 0.6 mm and support pillar diameter of 1.3 mm Maker spec. Those are PrusaSlicer settings for Prusa printers. For heavy solid models, Prusa also suggests hollowing or more and thicker supports.
• Use the pad or raft. Prusa's pad is a base the supports stand on, which it says gives much better stability than supports printed straight on the plate.
• Mix sizes where it helps. PrusaSlicer lets you set head diameter per point, so a fine detail can get a thin touchpoint while a load-bearing area gets a thick one.

Hollowing changes the force balance too: Prusa notes that hollowing lowers each layer's area and so the force needed to detach it. See Hollowing.

Removing supports

Formlabs' techniques: put flush cutters close to the part surface, work from the outside edges toward the center, use a hobby knife, tweezers or file for delicate features, and wear safety glasses because pieces fly. For when to remove them relative to curing, see Washing and Curing. Wear gloves while the part is still uncured.

If supports printed but the model did not, see Supports Printed, Model Didn't. If the print stayed on the film, see Print Stuck to the Film.