A resin print that peels off the build plate mid-print—or never attaches in the first place—almost always traces back to one of three things: the mechanical zero point, the light that cures the first few layers, or the condition of the surface meant to hold them. Guessing and adjusting all three at once changes nothing except the number of failed prints you generate. The approach here is to walk through the symptom, rank the likely causes, and test one change at a time until the bond is solid.

Leveling

What the symptom tells you

When the print fails to stick across the entire build area, or sticks on one side but not the other, contamination or exposure can still be factors, but a plane that isn’t parallel to the screen is the prime suspect. If the plate is flat but simply too far from the FEP film, no amount of burn-in exposure will compensate; the resin never gets squeezed thin enough for adhesion to overcome the release pull.

Before you touch the knobs

  • Remove the vat and wipe the LCD clean of any stray resin. A tiny dribble of cured resin on the screen can prop the build plate at an angle even when the leveling routine says it’s flat.
  • Confirm the build plate is seated tightly on its mount. A plate that shifts slightly during the first layer will lose contact on one edge.
  • Inspect the FEP film tension. A noticeably loose FEP can balloon upward during the plate descent, reducing the effective gap unevenly. This mimics a poor level but will not be fixed by re-leveling.

Ranking the causes

  1. The Z=0 gap is too large — the plate bottoms out against the paper or feeler gauge but the mechanical home position leaves a film-thickness gap that’s wider than the layer height plus an acceptable squeeze.
  2. Uneven leveling across the four corners — more common on printers with a single central screw or ball joint that can cant if the home procedure wasn’t done with even pressure.
  3. A worn or contaminated leveling surface — the paper card many printers ship with can compress over time, giving a false zero. Grease from fingers on the screen or the bottom of the plate changes friction and can trick the machine into stopping too high.

Walk through the adjustment, step by step

The goal is a consistent, parallel gap equal to one sheet of standard printer paper (roughly 0.1 mm) all the way around. I’d start with the manufacturer’s recommended card or a clean piece of 80 g/m² copy paper, not a crumpled post-it that was in a pocket.

  • Loosen the build plate screws so the plate can pivot freely and move up and down without binding.
  • Place the paper on the cleaned LCD and hit the “home” command—or lower the plate manually until it’s flat against the paper .
  • Press firmly on one corner of the plate with a thumb and feel for even resistance when tugging the paper from that corner. Do not hold the center; localized pressure near a corner reveals whether that corner is floating.
  • Repeat the paper tug at all four corners and the center. The drag should be uniform. If one corner slips freely while the opposite binds, the plate is tilted. Some printers let you “set” the home position after adjusting, others require a mechanical tramming with shims; follow your model’s sequence.
  • Tighten the plate screws in a cross pattern, lightly at first, then fully. Re-check one corner after tightening—plates can creep.
  • Set the Z=0 once you’re satisfied that the parallel gap exists. Some machines define “home” as the point where the motor strain peaks; others require you to save a manual microstep. Consult the procedure, but trust the physical paper feel over a sensor value that may be offset.

Common misstep: Leveling with resin already in the vat. That adds hydraulic resistance that can fool the homing sensor and leave a gap wider than intended. Always level dry.

If the paper test feels consistent but adhesion is still patchy across a large, flat print, consider using a 0.05 mm feeler gauge instead of paper for a gap tighter by half.The difference in consistent squeeze changes how much burn-in layer can bite.

Burn-in Layers

Symptoms of burn-in failure

  • Print sticks initially but separates from the plate after a few dozen layers, often leaving a thin, flexible pancake of cured resin on the FEP.
  • Corner s of a large footprint lift before the raft peels entirely.
  • The raft is glossy on the plate side and zero texture from the plate surface has imprinted.

None of those are leveling problems.They are the result of the initial cured layers not bonding strongly enough, not forming enough crosslink s into the plate surface, or being under-cured to the point where the motor’s peel force exceed. the bond..

Ranking the causes (after leveling is confirmed)

  1. Bottom exposure too short — the most common variable that gets adjusted blindly. Resin opacity and pigment load change required time dramatically .
  2. Too few bottom layers — typical recommendation is4–6, but some opaque or viscous cases demand up to10. The transition layer count also influences stress gradients.
  3. Light-off delay or rest time omitted — the plate mechanically lifts before the resin has stopped flowing back under the part, creating a momentary vacuum that peels the weakly cured layer.
  4. Ambient temperature too low — resin viscosity rises and curing speed drops significantly below 20°C, and bottom layers are most vulnerable because the resin is least warm at the start.

What to change, and in what order

Start by keeping a printed record: successful bottom exposure values for your resin with a decent raft. If you don’t have that baseline, pick the middle of the manufacturer’s recommended range. On a monochrome LCD that might be20–25 seconds for standard grey; for opaque blacks or engineering resins, expect35–45 seconds. An RGB printer commonly needs60–80 seconds.

Step 1: Bottom layer count. I’d make sure at least6 bottom layers are set, and8 if you’re printing a large solid part without a raft. Beyond10, returns diminish and you risk light bleed swelling the part dimensions near the plate. Set transition layers to a similar number so the exposure decline is gradual, not a cliff.

Step 2: Bottom exposure. If you already have6 bottom layers and the raft still peels, increase bottom exposure by5–8 seconds on a mono machine, or about12–15 seconds on RGB. Run one small test—a calibration square or a 20 mm cube sitting directly on the plate—and examine the raft. It should show a faintly matte texture where it met the plate, no gloss, and resist peeling at a corner from a fingernail.

Step 3: Rest / light-off delay. Add a1–2 second delay after the build plate retracts, before the UV array fires. This lets resin settle and reduces fluid drag that can lift the freshly cured layer. If your slicer uses a “wait before cure” setting, start with1 second and increase only if bottom layer quality does not improve with exposure alone.

Burn-in layer reference numbers

These are starting points for a monochrome printer at ~25°C with a well-leveled plate. Expect to nudge exposure up for dense pigment resins.

Resin Type Bottom Layers Bottom Exposure (s) Transition Layers Notes
Standard Grey 6 25 6 Lower to 22s with a fine-textured plate
ABS-like (grey) 6 30 6 Needs a bit more due to elasticity
Tough/Engineering 8 35 8 Viscosity demands more rest time
Opaque Black 6–8 40 6 Check for dimensional swelling
Clear/Translucent 6 28 6 Light bleed deeper; test adhesion patches

Resist the urge to run a full print after each adjustment. A well-adhered raft on a small calibration patch is enough feedback. Chasing two variables at once—like adding bottom layers and upping exposure in the same test—tells you nothing about which one mattered.

Surface Prep

Why texture matters

A shiny, mirror-smooth build plate provides almost no mechanical key for cured resin to grab. That’s why many manufacturers laser-etch or bead-blast the plate. Over time, however, those peaks wear down, resin residue fills the valleys, and skin oils create low-surface-energy patches that sabotage adhesion even when leveling and burn-in are spot on.

Common contaminant sources

  • Fingerprints. Every touch deposits a thin oil film. The effect is worse with IPA rinses that smear rather than dissolve.
  • Resin vat cleaner residue. Some cleaning solutions leave a film that IPA won’t fully remove unless you scrub.
  • Scratches from metal scrapers. Deep gouges from a steel razor blade can create a local dead spot where resin can’t make contact.
  • Oxidation on anodized aluminium plates. Especially if unused for weeks, a thin oxide layer reduces wetting.

The diagnostic test

After a failure, remove the plate, wash it with IPA, and wipe dry. Hold it under a bright light at a shallow angle. If you see shinier patches where the raft released, or a halo of residue that won’t wipe off with a paper towel, surface adhesion is compromised. A uniformly sanded surface looks dull across the whole area.

Prep that actually changes adhesion

Clean aggressively before you sand. Soak the plate in IPA for a few minutes, then scrub with a clean microfibre cloth or a soft toothbrush. For stubborn resin starch, a mild degreaser like a citrus-based cleaner can be followed by a thorough IPA rinse. Avoid acetone on anodized surfaces as it can damage the coating.

Light sanding for metal (but only if needed). If the plate is glassy smooth, a 600–800 grit wet/dry sandpaper used wet, with a flat block, can restore a micro-texture. Work in one direction, use light pressure, and check frequently. The goal is a uniform matte finish, not deep scratches. Wipe down thoroughly with IPA and a lint-free cloth to remove all aluminium dust before reinstalling.

Flexible build plates. If you use a flexible steel sheet with a magnetic sticker, contamination often hides under the sheet edge. Peel the sheet off, clean both sides and the magnet surface, then reattach pressed firmly from center outward. Wrinkled magnets produce air gaps that kill adhesion in patches.

Test after cleaning, not after sanding. If the plate was just dirty, a simple clean may be all it took. Sanding should only follow if the surface is too smooth and cleaning alone did nothing. Changing two variables at once muddies the diagnosis.

Preventing re-contamination

  • Handle the plate by the edges only after final IPA wipe.
  • After a print, remove cured parts with a plastic scraper or a razor blade used at a very low angle. Metal scrapers that dig in will create adhesive hot spots.
  • Every few prints, do a quick 30-second IPA wipe before starting the next job. Preventative cleaning stops the oil film from building up to failure point.

Testing your fix without chasing ghosts

Print a small calibration part that contacts the plate over a known area: a 20 mm cube, a flat 5 mm thick disc, or your slicer’s adhesion test print. Before adjusting anything else, note the result. If it sticks perfectly across the whole footprint, you’ve solved the immediate bind. If it still lifts on a corner, revisit leveling (that corner is likely high) before you increase exposure again.

Work one variable at a time. When adhesion returns, resist the temptation to immediately crank up all your prints; what solved the problem for a standard grey resin may need a slight exposure bump for a flexible resin later. But you’ll know the baseline, and that matters more than a generic profile.

There is no single “right” setting that works across every printer, every season, and every bottle of resin. The path to consistent adhesion is a methodical one: mechanical alignment, light energy tuned to the material, and a surface clean enough that the resin would rather stick to the plate than the film.