Three Lychee Slicer Problems and How to Fix Them
Lychee Slicer Field Log: Three Real-World Print Failures You Will Face
From a decade of dialing in MSLA printers not from reading the manual. Here's what actually goes wrong with Lychee Slicer and how to fix it without the marketing speak.
The Three Headaches
I've been running resin printers since the Photon S days, and Lychee Slicer is my daily driver. But it's not magic. The slicer can only do so much when the hardware and material fight back. After hundreds of failed prints and forum rants, here are the three issues I see most:
- Exposure time mismatch Lychee's resin profiles are often too optimistic for real-world conditions.
- Failed island detection The slicer's auto-support algorithm leaves gaping holes, especially on organic models.
- Corrupted or printer‑specific file issues Lychee's export settings don't always talk nicely to budget printers.
Issue 1: Exposure Time That Works in the Slicer, Fails on the Build Plate
You load a resin profile from Lychee's library. The simulation looks clean. First layer sticks, but halfway through you get a pancake on the FEP and a model stuck to the vat. I've been there more times than I care to count.
The physics, not the brochure
Resin curing is a function of UV intensity, temperature, and pigment density. Lychee's built-in resin profiles are tested in a climate‑controlled lab with a specific printer model. On your machine, the LED array may be 15% dimmer due to age, or the ambient temp is 18°C instead of 25°C. That "standard" 8‑second exposure for a grey resin becomes 10 or 11 seconds.
Workshop Rule of Thumb
I never trust the default exposure for the first print. Do a "validation matrix" the cones or the Ameralabs town. Lychee has a built-in test print wizard, but I still run a separate validation because the slicer's simulation doesn't account for real‑world light scattering. Expect to add 0.5 1.5 seconds to the slice's base exposure for the first two layers.
Field fix: The two‑print dial‑in
Step 1: Slice a small test model (say, a 20mm cylinder with a 0.4mm overhang) using Lychee's recommended settings. Print it. Look at the surface: if it's matte and has visible layer lines, you're undercured. If the overhang droops or the base is warped, you're over‑exposed. Step 2: Adjust exposure by 0.5s increments. I keep a log in a notebook the slicer's memory function is decent, but I've had it corrupt profile data after a firmware update.
One trick: Lychee's "advanced" exposure mode lets you set different times for layers based on area. In my experience, that's overkill for most models and can cause uneven curing if the resin doesn't have enough time to flow. Stick to a constant exposure unless you're printing huge drain holes.
- Common symptom: Supports break mid‑print → under‑exposed.
- Common symptom: Model sticks to FEP with no damage → over‑exposed.
- My go‑to resin: Anycubic Standard Grey + 9s at 0.05mm layers on a Photon M3.
- Don't bother: The "fast" modes in Lychee unless you have high‑power LEDs.
Issue 2: Island Detection That Lies to You
Lychee's island detection is good when it works. But I've seen it miss islands the size of a rice grain on complex models, especially with organic shapes like miniatures or jewelry. The symptom is always a failed support or a floating piece of cured resin in the vat the next morning.
Why it fails
The algorithm uses a raycasting method that works well on convex models, but on concave surfaces or interiors with lots of branching supports, it can miss thin membranes. Also, if you've rotated the model after generating supports, the islands might shift because Lychee only recalculates if you manually trigger analysis again. I learned this the hard way after a 12‑hour print turned into a solid blob.
Be Skeptical of "Auto Supports"
I've tested Lychee's auto‑support for over 100 prints. It's adequate for simple shapes, but for anything with overhangs steeper than 45°, it often leaves islands. My workflow: run auto‑supports at "medium" density, then manually inspect using the "island viewer" in the slice preview. Look for any red or orange highlights those are unsupported pixels. Add a single manual support to each one.
Pro tip: Use the "light" support preset for islands because heavy supports can cause suction cup issues. I've switched to using only "medium" and "light" never "heavy" unless the island is larger than 5mm in diameter.
The real fix: Manual island hunting
Step 1: After slicing, switch to the "layer" view and use the "detect islands" tool. It'll flash red dots. Zoom in. I keep a small notepad and mark the layer number. Step 2: Add a support at that exact pixel. I prefer a "light" support with a 0.3mm tip and 0.7mm contact depth. Step 3: Re‑slice and re‑check. I've caught islands as deep as layer 150 that would have caused a mid‑print delamination.
One personal annoyance: Lychee's undo history for support placement is shorter than I'd like. If you remove a support by mistake, you can't always Ctrl+Z back. So I save the project file before I start adding manual supports. You've been warned.
Alternative: Use the "support brush" tool instead of clicking each island. It's faster, but it can place supports inside the model if you're not careful. I only use it on flat surfaces.
Issue 3: File Exports That the Printer Refuses to Read
This one is a slow burner. You slice in Lychee, export as .ctb or .photon, copy to USB, and the printer either doesn't see the file, shows a corrupted image, or starts printing with weird layer artifacts. I've wasted hours on this.
Root cause: Format mismatch and encoding
Lychee supports many printer formats, but the exact version of the firmware matters. For example, older Elegoo Mars printers expect a specific .ctb v1, while newer ones want v4. Lychee's default export may not match your printer's actual firmware. Also, some budget printers cannot handle file names longer than 20 characters or with special characters. Lychee doesn't warn you.
My Export Workflow
- Always check the printer's firmware version before slicing. I keep a printed chart above my desk.
- Set file name to max 16 characters, no spaces or underscores. I use "mini_v2" not "Miniature_V2_2024".
- Use "USB transfer only" Lychee's network export can introduce latency corruption on some printers.
- Format the USB stick as FAT32, not exFAT. Printers are picky.
A specific horror story
I had a print that came out with shifted layers the infamous "z wobble" symptoms. I spent a week checking the Z‑rod, the gantry, the stepper. Turned out it was the file. I had exported with "anti‑aliasing" at 8x, and the printer's firmware couldn't process the smoothed edges fast enough, causing the layer images to load late. Switched to 2x AA and the problem vanished. Lychee's AA filter is good, but on older printers (like the original Mars), it's a resource hog.
Workshop Fix: The "Slice, Check, Print" Loop
Before a big print, always run a small calibration print first. I use a 5mm cube with the same exposure settings. If the cube prints cleanly, then I trust the export. I've also started using the "export to custom folder" to keep projects separate Lychee sometimes mixes up temporary files if you slice multiple prints in the same session without clearing the cache.
If the printer shows a garbled image, delete the file and re‑slice with "compression" turned off. Yes, it makes the file larger, but some printers choke on compressed .ctb files. I've turned off compression permanently after that shift‑layer incident.
One more thing: Lychee's support article says to use a specific USB stick brand. I've ignored that and used generic Sandisk sticks with no issues but I format them fresh before every print batch. A friend had a corrupted file because he left the stick plugged in overnight and it got a partial write while the printer was turned off. Always eject safely.
Final Practical Tips Not in the Manual
I've been using Lychee for four years, and these are the quirks I've learned to live with:
- If the slicer crashes during auto‑support generation, it's usually a memory issue. Enable virtual memory in Windows Lychee can eat 8GB on complex models.
- The "hollow" feature sometimes leaves tiny pinholes that cause the model to fill with resin. I always add an extra drain hole manually.
- UVTools is a better cross‑check for file corruption than Lychee's own verification. I run every export through UVTools before printing.
- If you see "suction cup" warnings in Lychee, do not ignore them. Add a hole or tilt the model. I once had a print pop off the build plate because of suction lost a full bottle of resin.
Mind the torque on the build plate bolts after you clean it. I've seen two people strip the threads because they overtightened while adjusting the leveling. The slicer won't tell you that.
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