Beware the invisible Jell-o!

After having a couple of prints in a row fail, I found that I had gelatinous blobs of semi-cured resin in my tank. These blobs are practically invisible when submerged in the resin. [unlike the cured bits which refract light slightly differently, and are thus slightly visible] The blobs tend to reveal themselves a bit when the resin moves around, due to the difference in viscosity. [I noticed it during the last failed print] Luckily I had already printed a strainer in anticipation of having to remove bits from the resin, though I had not expected this semi-solid gel. It does take some time and patience of going back and forth in different directions to get it all. But because the resin is thick like maple syrup, if you move slowly, the debris will not re-orient itself and slip through the holes in the strainer, [moving slowly will also keep the semi-cured gel from squeezing through the holes]

As a bonus, the strainer also works pretty well at gently removing failed prints from the bottom of the tank.

This is not 100% perfect, a finer strainer will get smaller particles out, but given the viscosity of the resin, it will take a LONG time to strain. If you find you have a lot of tiny debris causing problems, best is to toss it, and start with all new resin. [small bits are also likely only to cause small surface imperfections, and not entire failed prints]

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Congratulation for your graduation on the ‘fishing jelly fish bits from a resin tank’ major, these are good advice. :slight_smile:

I do agree it’s a pain, and I’m really wondering how you can even do it with the grey resin when we won’t be able to see through to grab the semi-cured blobs…

Maybe using a funnel and fine mesh to drain the whole tank slowly and pick the stuck pieces on the bottom?

SLT technology is definitely more messy than FDM…


I would consider a solution like this…Just have to determine the appropriate filter paper or mesh size to use and a hand pump vacuum… Just a thought.

Vacuum draw might break the gel apart, and allow it to pass through the filter.  Also don’t forget one would need to do all this in a dark-room, as this stuff is light sensitive. A paper filter, in a dark room or flask left to sit overnight might work. I’m actually going to try that on the IPA, to see if I can filter out the resin from it, to maximize its re-use before having to discard it.

vacuum pump…

Mark, I don’t think so…The filter paper would determine, what got thru.

I’ve encountered a few of these as well!  Sneaky… very sneaky!

Don’t worry about those tiny particles and jello stuff. That’s what the model base is for. To catch all that stuff. Just make the base thick enough and you are good to go.

The gel is troublesome, in my case it prevented the part and associated support structure from adhering to the build platform. The base is not for catching anything, in fact making the base and pins probably results in more of the stuff being generated! [The base and pins will likely trap most of the gel produced in that particular part, but some will still get out, particularly at the extremities]

The laser does not abruptly stop at the build thickness, but rather continues to travel up until the light is fully absorbed, or it hits the build platform. Now if there is a cured area above where the laser is exposing, this isn’t really a problem, as the spill-over will just further cure the part. But if it is in a overhang area, where there is just liquid resin, the resin there will partially cure, as the light no longer has enough energy to fully cure it. Prints like the Eiffel tower have excessive amounts of overhang, and thus likely produces quite a bit of the gel.

I printed a part with an undercut which turned a bit ugly when I tilted the part. Some of the geometry was missing when I pulled the part out of the machine so I went looking for invisible jello blobs before starting the next print. I’ll try to post some pics of what happened when I get a chance. I used a silicone spatula to slide bits of cured resin over to the side where I could pull them out with tweezers (don’t hit the tank bottom!). It’s fairly easy to spot the cured blobs in the clear (hold the tank up in front of a dark background),but  it’s going to be a pain to do it when the grey resin shows up.

I’m thinking of using a 60cc irrigation syringe (maybe with a special tip to avoid damaging the tank bottom layer) to pull out all the resin after scraping it into the corner with the silicone spatula. Either a filter cone  or a filter holder on the syringe would let me filter it before putting it back into the tank.

Does anyone have a sense of the level of “invisible Jello” formation on clean prints? I’d rather not clean out the tank every time I make a part, but I’d rather do that than try to fix parts with missing  geometry or other defects.

It’s exciting to finally be at the point of sorting out the process with this thing! I imagine we’ll all be pretty savvy about it in a few months.

Thirty days from today to find out if a known software solution can be employed otherwise you’re wait’n till February until it will be somewhat reduced.

My observation has been that the more undercuts you have, the more partially cured resin you get, so something like the Eiffel tower will tend to generate a lot of it.  If the geometry is fine enough, the bulk of that gel will stay trapped, and then be washed away in the bath.

Possible issues

  • A method to control an energy source used to cure/solidify the polymer, when not restricted by an already solidified layer of polymer behind the layer about to be cured the energy source will solidify the polymer to a greater depth than the build layer thickness. This occurs at component features such as over hangs, those areas of a build layer could then be delayed to a later build layer that corresponds to the cure depth of the polymer.

- laser optics and quality of the beam focus, umbra-penumbra and non symmetrical shape.

  • over shoot based on high inertia and g’s for the specification of the galvo’s

I have experienced a problem with holes and voids in my prints and blobs of jelly-like stuff.

I believe I inadvertently caused the problem by accidentally introducing some isopropyl alcohol into the tank on the build platform.

I’m currently draining my tank and will refill it with virgin resin (clear) and re-try.

Has anyone else noticed this from contamination with alcohol?

I think I  did the same thing (wiped the build platform down with alcohol and didn’t give it enough time to dry off). The problem got compounded by an overhang at the very end of the job which resulted in a bunch of uncured layers floating around. I’ve run the tray down to empty, so now seems like a good time to swap it out for new resin. I’ll let you know if things look cleaner.


The strainer is definitely a helpful tool to print. My preferred technique, though, is to just use my hand (wearing an **unpowdered **glove!) to remove cured or semicured bits from the tank.  If a print should go bad, I’ll use the scraper to free any stuck resin from the bottom of the tray.  Then I’ll just use my fingers to find and sieve out cured resin, taking care not to drip any resin from my gloves outside the tank.  YMMV.

I just managed to print the second half of my case for a patient monitoring device (third times the charm!). There was  a sliver of wall that didn’t fill correctly, and I’m assuming that this accounts for the moderate “invisible jello” accumulation in the tank. I did find a bit of well-cured resin on the tank bottom. I used a standard kitchen silicone bowl-scraper to dislodge the cured resin. I’m reluctant to use the steel scraper blade on the bottom of the tank ($95 a pop with shipping!). Maybe a scraper with rounded corners so you won’t dig into the silicone?

It would be great if Formlabs  could weigh-in on the issue with some suggestions for tank cleaning and for resin straining. It would be nice to have well-tested procedures established before we all have to go experiment with our own hardware.

From lots of hard won experience printing gyro cubes on the Formlabs print farm, I strongly recommend a plastic comb as a sieve for removing bits of pre-cured or partially- cured resin from the tank.  Large tines are best - I recommend getting a large comb and cutting it down to size so you can sweep the entire resin tank in a single pass.

I’m not sure how I’d feel using a Buchner funnel - the resin is pretty viscous, and you’d be exposing it to light during the filtration process.

Credit where it’s due - I got this idea from the awesome folks at Danger!Awesome in Cambridge.

Bear in mind, that if your resin is exposed to sunlight, it will eventually start to develop a granular or jelly-like texture, at which point it should be disposed of appropriately.

We’re working on an article about these techniques and hope to have it posted in a day or two in the help center.  Keep the creative ideas flowing - we’re never sure where the next genius usage tip will pop up!

To clarify on my technique, I’ll put on gloves and sweep the resin slowly, from front to back, with the comb.  When I get to the front of the tray, I’ll slowly lift it up at a 45 degree angle with the bits of pre-cured resin pressed against the side of the tank, and allow the good resin to drain out.  I’ll then lift the comb and uncured resin to a waiting paper towel and wipe off as much as possible.

Storing the comb in a sealed container of IPA means it stays clean and ready for use at a moments notice.

@Will Walker

Do you find the IPA from the comb affects the resin? Also, can you be more specific about light exposure. I work under a fluorescent strip light 4’ above my bench when I’m cleaning out the blobs. How long can the resin be exposed to this before it’s affected?

Thanks for posting.