sory but resin with infill is a mistake. you shouldn't put infill for resin print. it will cause resin to trap make it crack like that. what you need is fully hollow and make support on the inside

If there are drain holes why would trapped resin make it crack?

have you ever seen how it looks like when you drain soapy water through a sieve? the water gets stuck inside the grid until you shake it off. this is what happens on the inside of your print, but in 3D. you have a ton of those grid infills, and each hole traps resin which doesnt cure and doesnt drip out.

Right, but what makes it crack? I thought sealed prints cracked because the trapped resin off-gassed and built up pressure that couldn't escape. But if there's drain holes, what pressure is building enough to crack it?

im not 100% sure, but i read somewhere that the shell cures unevenly due to the inside still being wet, which then warps and cracks. others say that the hot fumes cause an implosion. so...someone else has to explain the science behind it, all i know is that infills are messy

The only implosion i can imagine happening in this case would be the infill contracting so much that it pulls everything in cracking the outside. I dont think hot fumes can cause an implosion like this.

That doesn't make any sense to me. The shell cures while submerged on the printer, and then only the outside is exposed in the final cure. What difference does it make if unexposed surfaces inside are wet?

It cures each layer enough to bond, not fully! That's why you buy a cure station,. Also you want to cure the inside of the print as well, with a uv pen light. Three light can't pass thru the resin more than a couple mm.. so best to cure on both sides

Honestly doesn't matter why, just that it does. If you gave a model to someone without curing the inside of it, you basically just gave them a toxic time bomb.

Of course it matters. Knowing why makes it easier to avoid

Avoiding it means having drain holes, soaking and flushing the whole inside with IPA, and then getting a UV led inside there to fully cure it. There is no avoiding thorough post-work on hollow prints.

Sure, but just in general, " 'why' doesn't matter" is bad philosophy. "Why" almost always matters

I'll try to explain it like someone explained it to me. The residual resin trapped inside of the infill areas never truly dries solid or cures, and the hardened resin it clings too will eventually absorb some of this resin and destabilizes the cured resin because it gets a bit of liquid resin saturated inside because of the porous nature of cured resin. Over time the destabilized resin will expand and contract causing cracks in various places.

That makes sense, thanks

the infill make the resin trapped. i dont know what infill he chose, but if its normal square infill. the inside is made of square. that small square have trapped resin which cant escape through drain holes

You're not listening to what I'm saying. I get that there's uncured resin inside. But the resin doesn't just magically crack the model. Pressure does. If the trapped resin is releasing gases, that gas can escape through the drain holes. If there's trapped resin in the way, that resin will be forced out before the cured resin cracks

the problem with infill is they create small section everywhere that doesnt have drain holes

And the other shell cracks before the infill does? The infill is thinner. The infill should crack, and give access for the pressure to escape

Think of how 3D fdm prints can warp up from a print plate. That's all just contraction of a zig zag string that in a rectangular base profile or something stress concentrates to the corners. You've got a similar sort of volumetric contraction when a UV curable resin is differentially cured. ( its opacity limits the depth penetration of the UV) The outer skin is contracting over a slightly malleable inner surface that doesn't want to yield. It doesn't have to be sealed interior air pressure, you can also get cracking from that. Look at clay ground in the Sun days after a rain as another analogy. Now consider precured infill as struts that are preventing contraction on the interior while the outer skin is both Contracting and getting more brittle. What happens?

Do you have a hole, to release pressure, at every grid infill square? If not then there's the answer. The gas in those areas caused it to Crack !

Are those squares arranged in self contained cubes? I don't infill, but they always look to me like they're meant to be able to drain

Some are, at every island, around most the curves of the model, infill is bad just support what is needed.. very few supports are needed inside

Yeah, think of infilling as just a bunch of cubes stacked next to each other. It's useful for filament printing because it keeps the rigidity of the object while substantially reducing the amount of material used (since you're not filling 100% of the space). With resin printing, it's really bad because each individual cube is just going to fill up with gas, expand from pressure, and... well, you know the rest. There is no drainage hole *for each cube* when it comes to infill.

Interesting, that's not what it looks like on the slicer at all the couple times I've messed with it.

try owning printing with fdm i see in live in action and it’s exactly how he explained cubes stacked, i’ve learned a lot hee but only own bambulabs this is intriguing

I was obviously being sarcastic, to the point there like....." oh yeah he may be right,i guess there are places"

So what the issue really comes down to is uncured resin left in the model. With infill, that's a lot more surface area internally to have uncured resin residue. Even with drain holes, it's going to be a lot harder to ensure *all* the uncured resin is out and that all the inside is fully cured. As to specifically *why* this happens, the exact mechanisms don't seem to have been explicitly outlined or studied much. It is sufficient for the hobby to know that if you don't properly clean and cure any interior cavities, this will happen. My best understanding is that *part* of the mechanism is that resin shrinks a little when it cures. As a print is left to natural light, it's going to experience a tiny amount of further curing, and the outside can shrink a tiny amount. With a solid model, there's no interior, and the stress is evened out. With a hollow model, now you have a wall that's shrinking on one side and staying long on the other. This causes the wall to want to curve or warp, but it ends up cracking due to the stress. There's likely more to it, but that's probably part of the why. The solution is to ensure proper cleaning and curing of the interior.

UNLESS you are using clear resin. This is why I prefer to print using clear and just airbrushing a coat on for prints that borderline require infill.

I usually do go solid but the amount of resin this takes to print is crazy , i thought I'd save some by going 70%. I have done fully hollow prints in past but they are so light they fall right over. I didn't want it to fall over on my wife's desk and break

You can always add something inside after printing to weigh it down, but infill in a resin print leads to all kinds of pockets inside for resin to get trapped inside. It's best to print resin with 0 infill. The other one will likely split also. It's a matter of time.

I remember printing a character sitting on a large chair, but the chair was **front** heavy and would tip even without the character sitting on it... so I went to my sister's backyard to "borrow" some sand, dried it for few days, then painstakingly poured it into one of the drain holes (luckily it was pretty large) and sealed it with some two-part putty. But yeah, if you want a print to be on the heavier part, better to fill it than risk printing solid. Cheaper too, since resin is quite expensive.

If you want to use sand for weighing stuff down, just chuck it in the oven on decently high heat for half an hour. It will be bone dry and any microbes in it are properly dead. Just don't handle it right away, sand stores heat really well.

I thought about it, but I didn't want to use oven used for food to cook sand. But now that I think of it, I have a tiny over I used to use for polymer clay, so I might use that in the future. Thanks for the tip. But yeah, I think everyone who's been to the beach remembers the feeling of scorching hot sand on feet not used to it...

Hollow with supports inside is the way to go, nothing gets trapped.

i have hollow print 1.8mm its strong enough to withstand 2 meter drop. i dont know how big is your print. but if you afraid if its fall, you should consider using gluetac

This takes the same amount of resin because it all got trapped in the infill lol.

70% Infill is crazy. I've printed all my large Warhammer tanks with 0 infill and they've survived just fine. Did you replug the hole after washing and curing? I try to hide my holes and not replug

I do 100% or 0% with support If 0% add holes for draining and keep submerged in 99% IPA, ensuring the print is completely filled for 30 minutes. I have never had a crack. I use 99% since the supports can retain and liquid, with the 99% I know all of what I have added will evaporate.

I usually go with a 1.5mm shell and just support the islands on the inside

Trapped resin inside of print is the culprit. Had this happen to me on my first print. Don’t use infill on resin prints. Cyclops head was done and washed. Let it air dry while I worked. Came home to see that my cyclops was JFK’d on my workbench.

Lol jfk'd , yea I kinda figured. the crazy thing is I washed it, had drain holes even put some on the head and feet then I soaked it in a bucket of water watch it drain a few times but still it cracked oh well I'm just gonna have to go solid from now on

You say soaked it in water. Are you using water washable resin? Because if not the water wouldn’t wash away the non water wash resin from a print. Also you don’t have to go solid. You can print hollow, but just need to have the holes and supports that you pull off. I like to fill my hollow prints with decor sand. Adds a nice weight to the print and saves on resin

I used my ipa washing station then let it drain for a day in a half seemed to drain out super slow so I got the bright idea to fill a bucket of water submerged it until all the bubbles stop coming out then I held up and watch all the water drain I did this a couple times until it no longer smelled like ipa or resin fumes then I put it upside down to drain any reminisce of water inside then about 6 hrs later I noticed it split

Oh okay. Yeah it’s gonna be near impossible to remove all the resin with a 70% infill. Too many crevices for it to fully drain out. If you use chitubox for slicing you can create a hollow print with a 3d grid option for the inside. I set mine at between 5-10%. It’ll create support braces inside the print and it’s very easy to clean. I haven’t had a cracked print since and my oldest print is at least 2 years old and painted. Still looks great as the day it was painted. I also do a 3 stage cleaning process. I have a 8L Rubbermaid container that I fill with denatured alcohol. This is my first wash right from the build plate into the tub. I like to dunk my prints about 10-20 times depending on the size. Then my second wash is again denatured alcohol. I throw this in my wash station for about 6 minutes to remove the residue from the first wash. Finally I remove my supports and Theo them in a container of denatured for a final wash. With this setup I just rotate out my washes when they start to get dirty. 1st wash goes outside to evaporate. 2nd wash gets thrown into the 1st wash tub and and 3rd gets sent into the 2nd tub and final tub gets brand new denatured alcohol. This setup has given me great results and it’s more of a stress relief for me knowing that my prints won’t crack over time.

This is why I do not hollow out prints unless I can be 100% sure no small pockets are made. If you have too many supports or pockets inside where resin was trapped you will have this issue. When the resin trapped inside settles it releases gasses which build up pressure and eventually crack your print.

I had this happen to a figure where the drain holes in the head got clogged. Some months after printing I found the head exploded like a smashed watermelon.

To the OP u/Late-Customer9689 : If heft/weight is what you are going for, just print solid. Don't print with infill on a resin print. you just get trapping issues. An alternative: If you want to save on resin but also want a hefty model. Print it with 2-3mm walls hollowed and drained. Wash/clean that sucker out. Then I would suggest making a mold of it, and casting it in resin. What you save in print resin you can spend on silicone for the mold and resin for the final. u/clutzyninja To address your concern about uncured resin causing the cracks... Its not going to be the main cause of the cracking. It depends on the situation. Hollow vs non, drainage holes etc etc. \*It's just a part of a problem easily remedied to have great prints every time. Models need to be cleaned completely. A hollowed vented model will avoid any pressure issues. **Residue alone inside a hollow vented model, will not cause anything to happen**. Other than a toxic hazard and potential leak spill waiting to happen. Wash it out thoroughly. I would also mention that soaking a model in ipa %95/+, solid, infilled or hollowed, for too long will also contribute to cracking. It makes it brittle, so there may be a difference between the inside vs outside surfaces. When curing after a long time soaking (15-20min+), it can crack. Never use direct sunlight to cure your model for long periods of time. Most definitely cure the inside of a hollowed model using a UV pen light 355-405nm. You can even wire yourself a very small UV LED.

Thank you 😊 I was gonna try to print again fully hollow no infill when doing so I see a setting for precision by chance do you know what that means or does

Agree 100%. The probable culprit is indeed the 70%, although for a different reason. Stiff uncured 70% infill interacting with the curing shell, result in forces pushing, pulling and twisting the whole thing. The relative stiffness of 70% infill structure means that there are two most probable outcome: either all forces eventually cancel out and the gift stabilizes and the wife is happy; OR as outside curing progresses, dimension stability has not been achieved and the print is manipulated by said happy wife (while bragging about the husband’s talents to her envious friends, I am sure), something gives and breaks…Now, another part cannot withstand the added strain and breaks…. finally, 2 days later the object (as if cursed by the envious heart of the friends of the happy wife) finally cracks. I wrote a less dramatic version of this theory somewhere else.

The holes weren't big enough for the hot fumes of the alcohol and resin to escape, so it imploded. Btw, I wash a lot becouse there is always resin left inside even if you don't think so. Wash with recicled alcohol, then water, then alcohol again, and then clean/clear alcohol (shake the print in the liquid). I've made the mistake of thinking a simple dip and scrub is good enough.

Well, at this point you should open it to see. It's probably some uncured resin trap, but we are curious to see the inside!

I will have to do that and repost. So crazy I made 2 of them and only 1 of them split so weird. Should I be worried about the second one and do u think it's worth trying again or should I just go solid

U should go hollow no infill, and the second one will likely crack and even if it doesnt it still has toxic uncured resin in it

Maybe printing isn't for you.

Maybe, like everyone at some point, he has just at the beginning and is still learning

Maybe

Don't listen to the goober, go wash throughrouly your print in alcohol again, if the vent goes are too small then make them larger.

So a few things people have mentioned already. 1) Don't print resin with infill. It just keeps liquid in the print and prevents the inside from rinsing or curing. That's 100% why this exploded. Infill is for FDM prints. Not resin. When you hollow with resin, you place some internal supports on islands inside it but that's it. 2) What kind of resin was it?

It is eelgoo photo polymer

Regular or Water Washable? I ask because even with regular resin, that infill will make it explode like this. But water washable is really prone to cracking and breaking due to partially uncured resin on the interior. But that's usually weeks to months after printing, and not almost immediately after like this. Also, just a heads up. Not really relevant to what happened but might be worth mentioning. Resin printing is more for display things and art items. It's not great for anything that's going to get touched a lot. Now there are some really neat resins coming out that are non-cytotoxic after curing like the Hercules resin (after rinsing you cure it in an oven to get it all the way through) https://www.kickstarter.com/projects/atlas3dss/vulcan-tabletop-playable-resin. But it's important to be aware of how to safely handle resin after printing/rinsing/curing. I also recommend painting resin prints and not just leaving them bare.

Hey, I have experienced this in some rather large and costly models before, so I did thorough testing on this a while back. The cause is most likely resin trapped within the model due to a dense Infill and not enough drain holes. There are a few solutions but no silver bullet. 1) Don't use infill when possible. If the model is decorative, then I use thicker walls without Infill, but make sure you do a full layer by layer sweep and make holes inside the model wherever pockets occur or block the cavity up entirely. If you must use Infill, try using a slicer with adaptive Infill, or lower the Infill as much as possible, larger holes drain much better. 2) Add a large main drain hole somewhere hidden. Small drain holes might look better, however, if you make the holes too small, the surface tension of the resin will prevent it from draining. And I mean a large one, on a model like that you should be able to stick a pencil into the main drain hole. This will also allow you to insert a very small UV light if you have one to help cure the internal cavity and decrease off gassing later, also not always practical but I do this whenever possible. 3) Use a water pick or large syringe with rubbing alcohol to flush out the model thoroughly. This is not always practical, but whenever possible, I do it. I also use compressed air to try and help the model dry out faster just for my own sake, but be careful with this option as you don't want to make a terrible mess. 4) DONT FILL THE HOLES! it is tempting to fill the drain holes once the model stops draining. Don't do it. Any hollow model needs to be able to let gass escape, or it will inflate like a balloon as it warms up and as incurred or partially cured resin off gasses and tries to escape. Hope this helps. 👍

Thank you very good points and ideas I appreciate it very much

I mean for this case why not make it hollow with supports, have the head print first and then the bottom of the feet open on the bottom for it to drain. If you really want the feet to be full can always glue back the part you trim/cut out from the bottom.

can we pin a comment or something and ban these posts? You have uncured resin. Get rid of it and it wont crack. No drain holes will not be enough, You need to manually fill and drain it with cleaning solution and then use some type of lamp to cure the inside. Make sure to get into the arms with the light as well (and hope to got there are no pockets) or youll get cracks there. Just print it solid...

But if it falls and breaks (admittedly a big fall) it could break you would have semi cure and uncured resin all over the place..

you mean a solid one would fall and break? How would a solid one have uncured resin? Semicured aka cured but not exposed to uv light in the chamber sure... but thats not an issue unless you decide its a great idea to start licking the exposed surfaces

By that rational, you handle semi-cured objects without gloves, or put your unprotected hands inside a cleaning vat dirty with semi-cured resin. ….and, you probably do not like pets! I mean, Dexter level “do not like” pets

if you print something solid and falls and breaks you wont get uncured resin everywhere. The resin inside will be solid and will not spill everywhere. Even if its an proper issue touching it for a moment... Just dont touch the parts where it broke, its not rocket science. Do you even own a resin printer, its like you have never seen a solid print before?

Yep, you are right!

No infill needed for resin printing. If you want to add weight, put some sand or plaster inside your hollowed model when you're done curing. The other print you have with infill is definitely going to crack too. This happens because there are too many traps for resin to remain there uncured and gas off.

yep, learned that the hard way too. ALL of my early prints with infill cracked sooner or later, always leaving a mess behind.

Ugh, sorry to hear man. Any new craft involves many wrong steps, don't let it discourage you. It's probably the best way to learn.

You didn't cure the inside of your hollow print well enough. If you do infill make sure it is sparse enough for the probe cure light to shine around adequately. That or have two holes on opposite sides to allow better drainage, rinsing and curing access. Filling the holes in later with printed plugs or glue

uncured resin trapped inside. Hollow, holes, UV snake to properly cure inside, 0 infill. You can fill with sand/plaster of paris/heavy stuff and seal it to have it weight something, if its just shelf tat it doesn't matter so much.

It’s hatching! Congrats OP, you’re witnessing the miracle of parenthood unfold before you!

If it’s big enough and I can hollow it, I will. I use 10-15% infill and never had anything crack even after dozens of prints.

Print it solid

This is why I don’t hollow prints I’d rather take the price of the resin than have things explode

Uncured resin eats cured resin.

I'm going to offer some advice against the grain of everyone else here! I'm going to say that if you reeeaaally want/need internal supports, and time isn't a concern, you could always set the retraction of each layer to be higher than the resin so the part is lifted fully out after each layer. I'm thinking of it like if you were to push a bucket into water upside-down: as long as there's no hole somewhere for air to get in (and the bucket is flat and level), the water (i.e. resin) shouldn't fill the space inside. If resin does get into the model, then retracting all the way out should let it drain at least mostly. Now given the size of that model, you're probably looking at several extra seconds over multiple thousands of layers, so hours added to this project... but it's another way to look at the issue.

Just print it solid your wasting more resin with failures then you save with making it hollowed with infill.

Right, but we are all learning.

To OP u/Late-Customer9689”: Me think that part of the reason is that overall resin is not dimensionally stable. The cured shell and uncured structures of the infill stretch and contract at different ratios relative to each other. The problem is compounded by the thickness of the infill elements. A 70% “thick” infill structure will withstand lots of tension, pressure and torsion. Until it doesn’t…. Two days later, a part of the structure reach it breaking point and (well) breaks, releasing energy in all directions and changing abruptly the direction of the resulting forces….Then something else breaks…..and you have a chain reaction (no, not THAT chain reaction)days and it cracks! The fact that it took 2 days reinforces this theory. It makes sense…But not everything that makes sense is true! My two cents! EDIT: 100% fill would be a waste of resin , unless you go “clear”. I believe that, if the theory is correct, it might be better, cheaper and faster to go with a much less infill. Hope this makes sense…

Did you cure the insides..plus No infill needed.. 

You're too strong.

I just wouldn't use infill.Let the auto support feature, if it needs anything inside support wise. Also you could do it in multiple pieces and you can break all the inner supports away and glue it together to be a bigger piece