A raft that vanishes from your slicer preview — or never generates at all — is one of the most frustrating surprises in resin 3D printing. You spend time orienting a model, adding supports, hitting “slice,” and then nothing shows up at the base. The print starts, your build plate dips into the vat, and the result is either a failed print floating somewhere in the resin or a bare plate dripping on the way up.
This isn’t bad luck. It’s a chain of fixable technical causes — and once you understand them, the solution becomes obvious.
What a Resin Raft Actually Does
Before diagnosing what went wrong, it’s worth being precise about what a raft is supposed to do. In resin printing, the raft is a flat, grid-like base structure that prints between your build plate and the bottom of your support columns.
Think of it as a foundation slab for a building. The supports are the columns, the model is the structure, and the raft is what keeps everything anchored to the ground. Without it, supports can pull free mid-print, releasing the model into the vat.
Why the Raft Gets Skipped During Slicing
Raft generation is not automatic in most slicers — it depends on a combination of settings that must all align correctly. If even one is misconfigured, the slicer either skips the raft silently or generates one that never makes it into the output file.
The Most Common Reasons a Resin Raft Fails to Slice
1. The Model Is Floating Above the Build Plate
This is the single most common culprit — and the most overlooked one. If a model was accidentally nudged upward on the Z-axis before saving, the slicer may technically place a raft at layer one, but the model (and all its supports) begins somewhere in mid-air.
The raft appears in the layer preview, the exposure runs, something cures — and then the rest of the print either falls into the vat or sticks to the FEP. The fix is simple: always check your layer-by-layer preview in ChituBox or Lychee and confirm that the raft starts on layer 1, not layer 10 or 20.
2. Raft Settings Not Saved Between Sessions
Certain slicer versions — especially ChituBox — have a known behavior where raft settings disappear if you return to the model view after adding a raft without supports.
The moment you toggle back to the standard model view, the raft is dropped. The fix: always add supports before applying a raft, or work directly inside the support view and do not switch back until you’re ready to export.
3. Slicer Software Bug With Specific Support Types
PrusaSlicer had a documented bug where enabling organic supports prevented raft layers from generating entirely. The G-code would export with a blank layer warning: “WARNING: Empty layer between 0 and 0.72.”
Switching to Grid or Snug support mode immediately resolved it. The takeaway: raft generation in slicers is tied to the support engine, not just the raft toggle. Always validate your settings after changing support styles.
4. Raft Thickness Set Too Low or to Zero
A raft thickness of 0.3mm to 1.5mm is the functional range for most resin setups. If someone has manually set raft thickness close to zero — or if default profiles were imported with stripped values — the slicer may generate a raft that is technically present but effectively invisible in the slice output.
The safe minimum is 0.3mm, which is about 12 layers at 25-micron layer height. Below this, the raft cannot reliably anchor supports or resist the peel forces during each layer lift.
5. Exposure Settings Breaking the Raft at the Layer Level
Even when a raft is correctly sliced, misconfigured bottom layer exposure can destroy it physically during the print. Over-exposure of bottom layers causes the resin to expand outward and create pressure that delaminates the raft — splitting it horizontally into two parts, one sticking to the FEP and the other to the build plate.
The key variables that create this problem:
| Setting | Too High Effect | Recommended Range |
|---|---|---|
| Bottom Layer Exposure | Raft delamination, elephant foot | 25–40 seconds |
| Bottom Layer Count | Excessive pressure buildup | 6–8 layers |
| Transition Layer Count | Mid-raft split | 8–15 layers |
| Lift Speed (Base Layers) | FEP suction pulls raft apart | 50–60 mm/min |
6. Resin Temperature Too Low
Cold resin is more viscous — it flows slowly and resists being pushed aside during each lift. When the build plate rises, the thick resin beneath the plate cannot escape fast enough, and this compresses the spring-loaded base plate, generating extra, unintended thickness.
This doesn’t prevent slicing, but it causes the printed raft to be far thicker than what the slicer shows — sometimes triple the intended value. Heating the resin to 25–30°C before printing allows it to flow correctly and match the sliced output.
7. Build Plate Leveling Off
An out-of-level build plate is a mechanical problem that manifests as an inconsistent raft. One side of the raft adheres well; the other side either doesn’t cure properly or sticks to the FEP.
The fix involves a fresh four-point manual level followed by a test print using a single flat tile before running anything complex. Never trust a saved level across multiple resin changes — temperature fluctuations shift plate height.
How Slicers Handle Raft Generation Differently
Not all slicers treat rafts the same way, and switching between them without adjusting settings is a frequent cause of the raft disappearing.
| Slicer | Raft Behavior | Known Issue |
|---|---|---|
| ChituBox | Raft drops if you return to model view without supports | Must add supports first, then raft |
| Lychee Slicer | Raft prints; model doesn’t adhere to it | Lift speed and height may need manual tuning |
| PrusaSlicer | Raft skipped when organic supports are active | Switch to Grid or Snug support mode |
| AstroSlicer | Brim setting auto-triggers raft even when disabled | Software bug — was patched in later version |
Fixing a Raft That Slices But Fails Physically
Sometimes the slicer shows the raft perfectly, but the print comes off the plate missing or distorted. That’s a different category of failure — and it has its own playbook.
Step-by-Step Correction Process
- Re-level the build plate before every new resin or major temperature shift
- Reduce bottom layer exposure to 30 seconds maximum, 6–8 layers
- Lower lift speed to 50 mm/min for base layers to reduce FEP suction
- Warm resin to 25–30°C using a warming pad or enclosure before printing
- Check layer-by-layer preview and confirm raft starts at layer 1
- Set raft thickness to 0.5–1.0mm — enough for adhesion, not so thick it wastes resin
- Enable “Rest After Retract” (2–3 seconds) to allow excess resin to escape before exposure
- Avoid over-large raft surface areas — bigger surface means more peel force, higher delamination risk
When the Raft Prints But the Model Doesn’t Follow
A raft sitting alone on the build plate — model nowhere to be found — is a specific failure mode. The raft cured correctly, but the supports couldn’t bridge from the raft to the model.
This almost always points to one of three things: lift height too low (the model can’t clear the FEP), supports too thin or improperly anchored to the raft, or the model being positioned at a height that prevents the supports from reaching it.
Check total lift height — it should be high enough to fully clear the FEP film plus the layer thickness. At 0.05mm layers with a 6mm lift, the math needs to work in favor of full peel, not partial.
Key Takeaways
- A raft missing from the slice preview is almost always caused by a model floating above Z=0, a slicer software bug, or raft settings not being saved before export
- Slicer-specific behavior matters — ChituBox drops rafts without supports, Lychee has lift speed sensitivity, and PrusaSlicer conflicts organic supports with raft generation
- Keep raft thickness between 0.3mm and 1.5mm — below 0.3mm the raft can’t resist peel forces; above 1.5mm you risk delamination and resin waste
- Bottom layer exposure above 40 seconds creates raft-splitting pressure, not better adhesion
- Cold resin is the silent culprit behind rafts printing thicker than sliced — warm your resin before every print
Frequently Asked Questions (FAQ)
Why does my raft show in the slicer but not print correctly?
The most common reason is mismatched exposure settings — specifically bottom layer exposure being too high, which causes raft delamination during the first few curing cycles. Lower your bottom layer count to 6–8 and keep exposure under 35 seconds. Double-check that the raft thickness in your slicer settings is at least 0.3mm.
Can resin printing work without a raft at all?
Yes — in many cases, a raft is not required. If the model sits flat on the build plate with enough surface contact, the bottom exposure layers alone can provide adhesion. However, for tall models with small footprints, or for models supported entirely by columns, a raft significantly reduces print failure risk.
Why does only the raft print and nothing else?
This usually means the supports are not connecting from the raft to the model, or that the total lift height is too low to fully peel each layer from the FEP. Check that your lift height is sufficient and that supports are properly generated and attached to both the raft and the model in the preview.
How thick should a resin raft be for best results?
0.5mm to 1.5mm covers most use cases. Thinner rafts save resin but risk failing under large models. Thicker rafts waste material and can increase delamination risk because more layers must be exposed at elevated bottom-layer exposure times.
Why does my raft appear thicker in print than in the slicer?
This is caused by cold resin being too viscous to escape from beneath the build plate during each lift. The compressed resin cures at excess thickness. Warming your resin to 25–30°C and enabling a Rest After Retract setting of 2–3 seconds allows the resin to flow out correctly before the UV light fires.
Does changing the support type affect raft generation in slicers?
Yes, directly. PrusaSlicer’s organic support mode is a documented example where raft layers are skipped entirely. Switching to standard grid supports restores raft generation. Always verify your slice output in the layer preview after changing any support style setting.
Why does my Lychee raft print fine but the model falls off it mid-print?
This typically comes down to lift speed and lift height being set too aggressively. When the plate rises too fast, suction between the cured layer and the FEP tears the model away from the raft before the resin fully cures. Reduce lift speed to 50–60mm/min for base layers and confirm lift height allows full FEP separation.
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