Resin 3D printed have issues, but one that I noticed is how resin 3D prints get split or crack. This is an issue that can really ruin your print quality, so I looked into how to fix those resin 3D prints that go through this problem.
To fix resin 3D prints that split or crack, you should ensure there is no uncured resin inside by hollowing your models and having enough drain holes for resin to leak out. Ensure you use a good enough normal exposure, so prints aren’t weak and under exposed. Don’t over cure your model and use a good wall thickness.
This is the basic answer that can point you in the right direction, but there is more useful information that you’ll want to know, so keep reading for more.
Why Do Resin Prints Crack or Split?
The most common reason for cracks or splits in resin prints is from uncured resin being left inside the model. Photopolymer resin or 3D printing resin goes through an exothermic reaction which means it gives off heat and expands as it cures.
This leads to an increase in pressure inside the model which, over time, can end up splitting the model and potentially popping. This is why you may see uncured resin leaking from these same cracks.
To make things simpler, I listed a number of reasons why a resin print may crack or split:
- Uncured resin on the inside
- Now hollowing your models properly
- Not having enough drain holes or them not being large enough
- Submerging the print in isopropyl alcohol (IPA) for too long
- Using a low quality, water-washable resin
- Not curing for long enough
- Curing resin prints for too long
- Printing with parts that are too thin
- Part orientation is leading to weakness in areas
Now that you have a better idea on why your resin 3D prints might split or crack, let’s get into the ways you can potentially fix this problem.
How to Fix Resin 3D Prints That Crack or Split
1. Hollow Out Prints with Adequate Drain Holes
One of the first things you want to do to fix resin 3D prints that crack or split is to properly hollow your models. Hollowing your models removes the inner material, leaving just the exterior or the walls around your model.
A lot of the time, your prints don’t need to be full of cured resin, so you can save resin in the long-run.
Once your hollow out your models, you want to learn where and how to place adequate drain holes to ensure resin doesn’t get trapped inside.
Preparing a resin print does require attention to detail to figure out where resin can get stuck, then adding a large enough drain hole to make sure it gets out.
A drain hole of 3mm usually works out fine for a normal-sized resin model. You want to try and add more than one drain hole because one is to relieve pressure, then the other to drain the resin out.
Pay attention to where the drain holes are in relation to the build plate because drain holes that point towards the build plate won’t help it leak out so great. You want at least one off them to be facing downwards towards the resin vat.
Ensure your drain holes are large enough and in the right locations. I’ve even heard that IPA may be able to evaporate and expand leading to failures.
2. Clean Out Prints Thoroughly & Drain Liquid
After you learn how to hollow your models in your chosen slicer, you want to ensure that the cleaning process is done to a high standard.
Cleaning out your resin prints thoroughly is important, as well as draining out all the liquid. I use the Elegoo Wash & Cure Plus to wash my resin models. It has an in-built ultrasonic cleaner which I filled with IPA.
I’ll usually clean most models for a minimum of 2 minutes, up to around 5 minutes for larger models. After the model is clean, I’ll remove the supports and try to clean up some of the marks.
Next, I’ll give it an extra wash by using a toothbrush so I can get it almost squeaky clean to reduce any white marks or residue on the model afterwards.
As long as you ensure any resin and cleaning solution is drained from your model, it should help fix models that crack or split.
3. Use a Good Wall Thickness
The strength of the model itself comes into play when models crack or split. Your wall thickness is one of the key factors to increasing the durability of your prints, so I’d make sure to use a good wall thickness.
The minimum wall thickness I would use is 2mm, increasing this to 2.5-3mm for parts that may need sanding or that I want more strength with.
You can see the walls below which is the white parts, while the hollowed part is the black parts in the middle. It’s a good thickness where it is more likely to be durable rather than some thin walls.
I created a hole in this hulk model, so resin can drain out and not cause cracks or splits.
4. Increase Normal Exposure
Another key part of part strength is your normal exposure time. When your exposure time is too low, you’ll experience under-exposure which can lead to flimsy or low detail parts.
Depending on your specific model, it can lead to splits or cracks due to essential parts of the print not being strong enough to hold the weight of the model. You may even get supports that don’t print all the way due to a low normal exposure.
You want to avoid these potential small fractures throughout the printing process.
I’d recommend increasing your normal exposure times to fix resin prints that crack or split.
An important thing to do before you even start printing your models is to dial in your exposure time settings using something like a Resin Validation Matrix V2.
This allows you to print a 5-minute model that has small details that show whether you are under exposed, have a good exposure or over exposed. The one I did below is slightly over exposed as you can tell from the rectangles at the bottom.
They are slightly bigger than the gaps in between.
5. Make Sure Residue is Clear From Resin
A less common but still potential issue is ensuring that your resin is clear from residue or small bits of cured resin from previous models.
If you aren’t careful, you may experience prints cracking or splitting due to cured resin floating around in the resin vat. It could easily float into part of your model and ruin an essential part of your model.
This is a less likely cause of cracking or splitting, but still a possible reason.
Make sure you filter your resin out from the resin vat properly. I like to use my plastic scraper to move around the resin to see if there is any residue after each print.
6. Use Resins with More Flex & Avoid Water Washable Resin
If your parts have splits or cracks due to weakness or being brittle, using a resin with more flex or bend can definitely help fix this issue.
A good resin with a decent amount of flex are some of those ABS-Like Resins on Amazon. You’ll be surprised how much some resins can bend compared to others.
Another useful thing you can do that many users have successfully done is to partially add flexible resin like Siraya Tech’s Flexible Resin (Amazon) to the resin vat.
It can reduce the effects of cracks or splits in your models from a strength standpoint. These are also said to shrink less than other resins, and since shrinkage can cause cracks, it works in your favor.
7. Remove Supports Before Curing
Sometimes you may accidentally crack a model from the post-processing and dealing with supports. Most people recommend that you remove supports before curing since curing them makes it harder and more difficult to remove.
A compromise could be to flash cure your model for a few sections, so the model is not too weak, but this could lead to those white marks you tend to see on models after curing.
Personally, I just make sure to use a good normal exposure time and create my supports in Lychee Slicer which tend to be easy to remove in my experience.
8. Avoid Printing Parts Too Thin
A few users have ended up with splits or cracks in their models simply due to printing with parts that are too thin.
In some instances, you can’t do much about printing thin parts with specific models, but if you have some design skills, you could possibly increase the thickness of some areas.
I think adding a flexible resin as mentioned above could definitely help solve this issue. Another good fix would be to ensure your exposure times are dialed in.
9. Don’t Leave Parts in Isopropyl Alcohol for Too Long
AmeraLabs did an experiment to see the effects of leaving resin 3D prints in IPA for certain periods of time to see the effects. They found that if you leave models submerged in isopropyl alcohol, it is likely to lead to cracks or splits in your models.
I’d avoid leaving your models in your cleaning solution for too long, especially if it contains alcohol.
You could opt in to use other cleaners which don’t have such strong concentrations of alcohol or products like Mean Green and Simple Green.
Anywhere from 1-5 minutes should be enough depending on the size of the model.
10. Don’t Over Cure the Model
Over curing resin models can definitely lead to increased brittleness due to the reaction of light on photopolymer resin. You don’t want to leave your models under strong UV lights for too long.
A standard time for curing models ranges anywhere from 1 minute to 5 minutes for larger models with a decent UV light.
You could run your own tests by printing 5 of the same models, washing all of them as normal, then running each one under a different curing time to see how it affects the model.
To avoid splits or cracks in your model over time, you want to ensure your cure times are at a good standard.
11. Use a Larger Layer Height for Strength
If you happen to use lower layer heights such as 0.01mm or 0.025mm, it could have a negative effect on the strength of your model. It’s not a usual cause for cracks or splits but it could potentially contribute.
After trying many of the fixes above, if you find that your models are still splitting or cracking afterwards, I’d try to use a more standard layer height of 0.05mm.
12. Use an Optimal Part Orientation
The part orientation for resin models does have a significant effect on how your prints come out. Using the wrong orientation can really decrease your part strength and surface quality.
I’d recommend learning how to create the optimal part orientation for each of your models because there will always be many things to take into consideration.
Similar to the part about printing thin parts, you may be orienting a model in a way that layers run at an opposite angle to thinner parts.
An example would be a cape on a model. A cape usually falls vertically, so you could orient the model to print horizontal lines across the cape by having it perpendicular to the build plate, or at a 90-degree angle.
I’m not sure how effective this would be, but it seems as though it should have a positive impact on reducing splits or cracks in models.
A good part orientation could also help to reduce the weight of a model on weaker sections. The weight of your models can cause them to slowly pull away from the build plate, so you could spread out the weight by using a different print orientation.
13. Drill Holes into Model to Drain Resin
Once your model has been creating and not hollowed out, there’s not a lot you can do but wait for the model to cure. I’d recommend leaving it in some kind of closed container so it doesn’t leak onto other things.
What you could potentially do is to drill holes into the model to try and drain out the resin, but this is obviously a potential safety hazard as resin could pop out.
I’ve only drilled into a resin model that was hollowed where the drain holes didn’t quite reach the correct areas. I’d avoid drilling into a resin model that isn’t hollowed.
I used the Ginour Cordless Rotary Tool from Amazon to get this done.
If you find that your model has cracks and is wet, you want to quickly put your gloves on and clean up any leaking resin off the model and surrounding area with paper towels. You can also wash it in your cleaning solution.
You can leave the part in the sun to cure fully, ideally in a container or underneath some paper towels.
Another fix could be to actually fix the cracked model by filling it with uncured resin and curing it. Then to reduce the shine, you can scrub it with a toothbrush and IPA, along with sanding so it blends in with the model better.
Hopefully this article helps you to understand and fix the issue of cracks or splits in your resin models.