Been chasing this for two weeks. Every print would come off the plate with these little raised bumps in the first few layers, like someone sprinkled gravel into the bottom. Re-levelled the plate twice, swapped to a fresh bottle of resin, even lowered my lift speed. Nothing changed. Then last night I took the vat off and held it up to the light. There was a thin cured film stuck to the FEP right where my prints always sat, leftover from a print that failed on me ages ago. Every cycle after that, the screen was burning through that cured spot and curing a little patch right onto whatever was printing below it. So the blobs were basicly ghost prints of an old failure. Scraped the film off gently with a plastic scraper, wiped the FEP with IPA, filtered the resin through a paint strainer to catch any floating bits, and ran a test print this morning. Perfectly clean base. Zero bumps. Wish I'd checked the vat itself two weeks ago instead of blaming my settings the whole time. If your prints suddenly grow random lumps in the first layers out of nowhere, look at the FEP before you touch anything else.
Finally figured out the random blobs showing up in the base of my prints
Oct 19, 2026
Last reply: 2 hours ago
5 Replies
I burned a whole week on something like this on my Saturn 4 last spring. Mine wasn't cured film stuck down though, it turned out to be a small scratch on the film itself from when I got impatient prying a stubborn print off the plate. The scratch let light through a little differently and every print after that had a lump in roughly the same spot, just off center. I kept re-leveling and tweaking burn-in layers like a fool before I thought to look at the vat. What finally worked was pouring the resin out and holding the empty vat up to a lamp. The scratch showed up as a faint bright line I could feel with a fingernail. Swapped in a spare sheet of film, tightened the frame screws evenly in a criss-cross pattern, and the lumps were gone on the next print. Now the lamp check is part of my routine every time I clean the vat, takes two minutes. I also strain resin back into the bottle after any failed print so loose cured bits don't get a chance to float around and stick somewhere. You're right that the vat tells on itself long before the settings do, and the Saturn makes it easy to pop off and inspect compared to some printers I've used.
For me the culprit was on the other side of the film entirely. Had a run of prints last month on my Saturn 4 where the bottom couple layers had this one hard nodule, same spot every time, dead center-ish. FEP was spotless, plate was level, resin was fresh. Nearly lost my mind. Turned out there was a speck of dust sitting on the LCD screen itself. Light was leaking around it just enugh to cure a little extra puck on every exposure. Took a microfiber cloth and a couple short puffs of air, wiped the screen, and the next print came out clean. I hadn't even had the vat off that day, so no clue how the dust got in there, but it did. Now whenever I see lumps that repeat in the same place I check the screen before the film, and if the spot moves around between prints then I figure it's something loose in the resin and go straight for the strainer. Two different symptoms, two different fixes.
The old blank exposure trick catches this stuff too. Pull the vat, leave it empty, and run a full layer cure. Any cured ring or dot on the FEP after that shows you exactly where the light is getting blocked or scattered. Learned that back on my first Photon when I chased a mystery bump for a month. Also, once you've had this happen you stop trusting a quick visual glance. Cure film can be nearly invisible til you drag a fingernail across it slow. Cheaper than burning another two weeks on settings that were never the problem.
I had lumps on my first few prints too and it turned out my hands were the problem. I'd been grabbing the sticky stuff off the plate with bare fingers and left tiny smears, and the next print copied those smears into the bottom layers. Now I put gloves on before touching anything that ever touched the liquid. So how do you know when that clear sheet in the bottom of the tub is too worn out and needs swapping for a new one, does it just look cloudy after a while?
I found something similar once where the film was perfect and the resin was clean, but the prints still had bad spots. It turned out the build plate itself was slightly marred. It wasn't a big scratch, but maybe some cured resin dripped onto it or it had tiny dust grains baked in from previous failed prints. When the resin cured onto that slightly contaminated spot, it just kept blooming outwards in the base layer. I had to gently sand the plate surface before trying again. It’s wierd how often the surface condition of the plate is overlooked when everyone is focused on the vat. Has anyone tried putting a fresh coat of primer or a bonding agent on the plate before a big job? I'm wondering if that helps stop the initial layer from catching imperfections.
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