3D Printing Troubleshooting: All SLA Issues and Solutions

Layer shift on an SLA printer looks like a step in the Z direction, but it is rarely a mechanical fault. In most machines the cause is a loose build platform, a worn lead screw, or resin that has thickened at the bottom of the vat. Check platform runout with a dial indicator first. Anything over 0.05 mm of play means the platform needs re-torquing or replacement before you touch the exposure settings.

Blooming is the opposite problem. Overexposure pushes light into the previous layers, so edges grow wider as the part rises. You see rounded corners, lost holes, and a part that measures 0.15 mm oversize across a 20 mm feature. The fix is exposure. Run an exposure matrix, then reduce the normal layer time by 10–15% and the bottom layer time by 20%. Keep the bottom layers long enough for adhesion, usually 5–8 times the normal exposure.

Exposure also shifts with resin temperature. A vat at 20 °C needs more energy than the same resin at 28 °C. If your shop swings 8 °C between morning and afternoon, expect dimensional drift on tall parts. A heated vat or a temperature-controlled room removes this variable. For production parts, log vat temperature next to the exposure setting.

• 1
  Platform play over 0.05 mmRe-torque or replace the build platform before adjusting exposure.
• 2
  Blooming on cornersCut normal exposure 10–15%; check hole diameters with pin gauges.
• 3
  Cold resinBelow 22 °C, expect longer cure and higher dimensional drift on tall parts.
• 4
  Tall parts, one sideRotate the part so the tallest feature is not at the peel edge.

Warping on SLA usually starts at the peel side. As the platform lifts, the cured layer sticks to the film and pulls the part. Thin flat panels bow; long brackets twist. Tilt the part 10–20° off the platform so each layer has less cross-section to peel. Add a raft only when the part is small and the footprint is narrow. A raft on a flat panel makes the warp worse by locking the first layers in place.

Cupping is a hollow section that traps resin and creates suction against the film. You hear a pop during the peel, and the part may delaminate near the closed end. Drain holes fix this. Put a 2 mm hole at the lowest point of every closed cavity, and a second hole at the highest point so air can enter. For a 30 mm cube with a hollow core, two holes are enough. For long channels, add a hole every 40 mm.

Support scars are a finishing problem, not a print failure, but they decide whether the part is usable. Contact tips that are too large leave pits on the surface. Tips that are too small let the part peel away. Use light tips (0.2–0.3 mm) on cosmetic faces and heavier tips (0.5–0.8 mm) on hidden faces and overhangs. If a face cannot carry any marks, orient it away from the supports or plan to machine it after printing.

• 1
  Flat panel warpsTilt 10–20° and drop the raft; reduce peel speed.
• 2
  Pop during peelAdd a 2 mm drain hole at the low point and a vent at the high point.
• 3
  Pits on a cosmetic faceUse 0.2–0.3 mm tips on that face; move heavy supports to hidden geometry.

Under-washed parts stay tacky and grow a white film after cure. The film is uncured resin that has absorbed moisture. Wash in two stages: a dirty bath for 2–3 minutes to remove the bulk, then a clean bath for 1–2 minutes. IPA at room temperature works; warm IPA attacks some resins and softens fine features. If the part has thin walls under 1 mm, cut the first wash to 60 seconds and check.

Post-cure adds strength but also shrinks the part. A typical acrylic-like resin shrinks 0.4–0.8% during cure, and the shrink is not uniform. Thick sections shrink less than thin ones, so a 100 mm bracket can move 0.3–0.5 mm after 30 minutes under UV. Cure in short cycles and measure between them. For parts that must hold ±0.1 mm, cure first, then machine the critical faces.

Dimensional drift also comes from the printer itself. SLA holds ±0.1 mm on a well-tuned machine, but the error grows with part height. A 150 mm tall part may show 0.3 mm of Z error from peel forces alone. If your tolerance is tighter than ±0.1 mm, or the part has to fit a machined mating surface, SLA is the wrong process for the final part. Print it for form and fit, then cut the critical geometry on a CNC.

• 1
  White film after cureTwo-stage wash; keep IPA at room temperature.
• 2
  Shrink after UV0.4–0.8% typical; cure in short cycles and measure.
• 3
  Tolerance tighter than ±0.1 mmPrint for form, then machine critical faces on a CNC.

SLA is good at smooth surfaces, fine features, and small parts with organic geometry. It is a poor fit for load-bearing brackets, threaded holes, and any face that has to seal against another part. Cured resin creeps under sustained load, and a thread printed in resin strips at low torque. If a part carries a bolt, cut the thread after printing or switch the part to aluminum.

The break-even point is usually around 50 to 100 parts, or any part where two dimensions must hold tighter than ±0.1 mm. Below that, SLA and CNC both work, and the choice depends on geometry. A part with deep pockets, sharp internal corners, or a sealing face goes to CNC. A part with a smooth shell and no critical fits stays on SLA.

For functional prototypes, we often run both. Print the housing on SLA to check the feel and the cable routing, then machine the mounting plate and the connector interface on a 5-axis mill. The printed shell confirms the design; the machined parts confirm the fit. That split avoids a second round of tooling when the design changes.

GreatLight runs SLA for prototypes and CNC for production parts, with ±0.005 mm tolerance on machined features and Ra 0.8–1.6 μm as a standard finish. If a printed part fails the same way twice, send us the file and the failure photos. We will tell you whether the fix is in the print setup or in the process choice.

• 1
  Threaded holesResin threads strip; cut them on a CNC or use inserts.
• 2
  Sealing facesMove to machined aluminum; SLA surfaces leak.
• 3
  Sustained loadResin creeps; metal holds.