Can You Over Cure Resin 3D Prints?

This question is considered controversial among the 3D printing community, and different sources will have varying opinions on the matter.

Some people deny that over-curing resin is even possible, while others consider it safer to over-cure your project rather than under-cure it. There are even a select few people who argue that over-curing can damage your piece and should never be attempted. So, who is right?

In a nutshell, if you leave resin print in your UV curing machine for longer than the recommended time, then you should expect your final piece to be affected.

Over-curing is often considered an inevitable part of the process, as the UV rays emitted by the sun will continue to cure your resin print gradually, sometimes years after the piece was first made. 

Some companies will claim that their resin prints will not experience changes due to over-curing. However, this isn’t entirely true as it’s often impossible to completely stop the piece from becoming brittle over time due to exposure to UV light.

What Is Meant By “Over-Curing”?

Over-curing is a phenomenon that occurs when UV light continues to cure resin print even after the user believes it has fully hardened.

This most commonly occurs when the user leaves their resin 3D print in their UV curing station for longer than the recommended amount of time. Over-curing is also sometimes caused by extended exposure to UV light such as sunlight, but this is far less common.

While some UV light exposure is essential for the hardening of a resin print, too much can have negative effects on your final result. UV light damages all organic materials, including resins.

So if you use extreme UV levels while curing, it would degrade (or over-cure) your resin print and cause brittleness. Over-curing can also happen if you keep the resin-printed part in your UV station for longer than necessary.

The degradation effect of the UV light doesn’t just apply to resins. It occurs with all organic materials. However, the degree of degradation differs from one material to the other.

There are different types of resins with varying sensitivity to UV light. The UV-sensitivity of your material will determine how fast it will degrade under UV exposure and the wavelength that’s sufficient to cause degradation.

Once the piece reaches optimal stability and hardness, UV exposure should be stopped or limited as much as possible to keep your work intact. Over-curing a 3D resin print will make it brittle, not stronger.

How Long Should Resin 3D Prints Be Left to Cure Under UV Light?

The amount of time your 3D resin print will take to cure depends entirely on its size. Miniature prints can take less than a minute to cure- under a UV lamp of course.

Curing 3D prints using direct sunlight is possible, but this runs the risk of dust falling into the piece and curing within it. A UV lamp or chamber is the best curing method, and the results are pretty much instant.

In order to achieve an even cure, your piece should be rotated while it’s under UV light. Most curing stations come with rotating platforms for this purpose.

If you’re using engineering-grade resin, consider leaving it in sunlight after curing it under a UV lamp as it takes a little longer to achieve the strength and rigidity that it requires.

How Do You Cure 3D Resin Prints Without a UV Lamp?

Yes. It is possible to cure 3D resin prints without a UV lamp. However, the only other alternative is curing them under direct sunlight. While this method is great for preventing over-curing, it does also pose a lot of problems.

For example, you’ll need to be able to guarantee access to direct sunlight for a minimum of 20 minutes - which isn’t always easy for those who don’t live in sunny locations. If there happens to be a change in weather and the skies cloud over while your 3D resin print is curing, it will not cure evenly.

Some larger pieces will require direct sunlight for much longer periods of time. You shouldn’t attempt to cure your 3D resin prints through a window as this can hinder the curing process. This means it’ll need to be left to cure outdoors, so be sure to check the weather forecast before working with resin!

Relying on direct sunlight to cure your 3D resin prints can also be time-consuming, which is probably why it’s avoided by most professionals. Those who make prints on a regular basis will often use a UV lamp or UV chamber to cure their creations.

If you’re planning on making multiple models, you’re going to need a UV light. However, over-curing is far more likely to occur when using a UV light, so we recommend checking it regularly while it’s curing.

Alternatively, you can cure your 3D resin prints in a UV chamber. These chambers use a heat bulb to cure the resin under temperatures up to 30 degrees celsius.

Again, it’s possible to over-cure your resin print in a UV chamber, so you’ll need to keep a close eye on it.

Some artists even claim that it’s possible to cure prints in an oven at a high temperature, but this is risky in terms of over-curing and should be avoided.

Is Smoking Resin a Sign of Over-Curing?

If your resin looks like it is smoking, there’s no need to panic. What you’re seeing isn’t actually smoke at all, it’s just steamy vapor that occurs during the curing process.

This nothing to worry about and it does not correlate with over-curing. However, resin vapor can be toxic if inhaled, so make sure that you’re working in a well-ventilated room with the correct PPE.

UV resin curing involves an exothermic reaction, which essentially dissipates energy from resin in the form of heat.

As the heat escapes the resin and meets the air, it vaporizes and creates this visible steam. It can sometimes get quite intense but it isn’t burning.

Can you use LED UV Light to Cure 3D Resin prints?

It is possible to cure UV resin with an LED UV flashlight or lamps.

As LED light isn’t as penetrating, your light must have a minimum wattage of 4, but we recommend using a light with a wattage of 9 or above.

What Causes Tacky Resin?

Tacky or sticky resin is usually caused by under-curing. So, while you need to be cautious of over-curing your prints, not enough can be just as damaging to your final result. If you don’t cure your 3D resin print for long enough, expect it to feel a little sticky.

Tacky resin can be avoided by curing the UV resin in layers, slowly under a weak UV light. This will ensure that your piece is completely cured, right to its core.

Be sure to follow the specific instructions provided by the manufacturer. Once your 3D resin print has completely cured, you can go ahead and wipe it clean with a Q-tip and rubbing alcohol to remove any sticky remnants.

When cleaning a sticky resin print, you’ll need 2 separate containers of IPA. You’ll need to wash the print in one container with IPA which will eliminate most of the liquid resin. In the second container, fill with IPA, dunk the print inside and give it a shake. This will help to remove any remaining resin completely from the prints.

Another great way of solving issues with sticky resin is by allowing them a little more time to cure under a UV light source. This is easy to do and it should come up as good as new once sanded after curing.

Sanding shouldn’t be overlooked- not only does it provide an even and shiny finished surface, but it can also eliminate pesky sticks patches and imperfections too.

What Safety Precautions Should You Consider When 3D Resin Printing?

Any activity that involves liquid resin has its risks, but it is relatively safe to use as long as it is handled with care and respect.

Once your piece has completely cured, the resin will no longer emit toxic vapors and your model will be safe to handle.

Before this, however, it is recommended that you always wear gloves when handling uncured liquid resin.

When working with resin, you’ll need the following PPE:

  • Nitrile gloves
  • Face mask (ideally a respiratory mask)
  • Safety goggles/adequate eye
  • An uncluttered and well-ventilated workspace

Why Do My 3D Resin Prints Smell So Bad?

It’s pretty normal for the resin to come out a little stinky once printed, but this should mostly be eliminated by the cleaning process mentioned above.

However, if your 3D resin prints still have an odor even after you’ve cleaned them and they have completely cured, there are still a few options you can try.

Firstly, consider ditching the isopropyl alcohol if you’re working in a small indoor space. It has quite a strong odor and the fumes can become overwhelming and nauseating. 

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