Clear resin cracks


I just ordered three new clear resin bottles as mine was finished. These 3 bottles contain the new V2 Clear resin. The clear resin I still had was V1.

I’ve printed an object in the old clear resin as a prototype and want to print the proper object in the V2 resin as doesn’t turn yellow over time, however then print comes out all cracked and brittle with the new V2 resin… What could be the reason for this?

The printer prints fine in all other colors (and it printed fine with the clear V1 resin)…

I noticed that the Clear V2 resin was much harder when trying to get it off the build platform, however the resin seems so brittle that it gives major problems with printing…

This is a photo of the print with V1 Resin. No problems here:

And this is a print with the V2 resin… As you can see it’s brittle, cracked and the surface of that area is rough as well.

Here;s both of them next to each other for comparisation.

What’s wrong with this new V2 resin???


Did you print these in the same orientation?

I printed them both in the same orientation and on same place of the build platform.

I made another test print afterwards on a differnt part of the build platform which gave me the same brittle result (a little less, but still brittle). Therefore I did a full test print overnight where I placed them on the four different corrners of the build platform to see if it was only in certain places of the build platform. I placed them in the same orientation again. The only difference was that I printed them in .1mm instead of .05mm.

The prints came out fine this time…



I have to note that the original V1 resin print was .1 as well. So the prints seem to fail in .05mm… I don’t know why… Of course the peeling of the layers will double at .05 but it shouldn’t give these sort of results in my opinion??

From my experiences with Thicker parts you have to be at the .1 resolution anything less and you are asking for trouble

I guess you’re right. However, I would like to know why this happens instead of just accepting that this happenns.

Perhaps someone from the Formlabs team can clarify a little more?

Alright I see whats happening here. The problem is you have a closed cell of uncured resin which causes the blowout. The reason it fails on 0.05 and not 0.1 is not something I know the technical details of however is something I would expect. The 0.1 resolution seems to be stronger and less susceptible to blowouts and 0.025 seems to be the worst. I imagine it has something to do with the power level of the laser having to be higher to cure through the 0.1 layer thus curing the majority or the layer more, but the dynamics of curing resin are a mystery to me.

So the solutions involve either reorienting your part or editing your part or both. You want to do this so that you do not have a closed cell of uncured resin. To check for a closed cell move the layer view slider up slowly checking for an area that is completely cured on one layer and as you move up the higher layers get a hole in them surrounded completely by that cured area. This creates a kind of cup in the model at that stage which when pressed into the PDMS acts like a suction cup. The pressure difference created from the peel and return process is so great that it blows through the side walls of the cup if they get thin enough. So the trick is to orient your part so that any cell like this has a hole between it and the build platform so the cup is never formed. If you can’t find an orientation that does this that you are happy with you can add a hole to your part to prevent the cell being closed.

I think you might be on to something here! Although there aren’t any closed cells in my print. There is a shallow part which goes towards the middle of the print (the 2 circles). Though they are open and are never fully closed off, causing the air/resinpocket, it is a very deep and thin “canyon” and therefore, the pressure might still be too much creating a similar effect.

One thing that doesn’t make sense is that those brittle/cracked parts have still not cured and are sticky, eventhough it’s nearly a week ago and they’ve been sitting on my desk this whole time. This seems strange, as I would assume that it would have cured entirely and hardened entirely over time…

But thanks for your feedback Rocus, Your explanation seems plausible!

The closed cell I’m referring to does not mean completely enclosed in the final print. It means at some point in time during printing when the print is pressed down onto the PDMS the PDMS completely closes the cell. So for example if you print a shot glass upright with supports. First the supports print, then the bottom of the glass will print creating solid layers, then as you continue you will be printing layers in the shape of rings. When these rings are printing a closed cell is created. The walls of this cell consist of the bottom of the glass that has already printed on one side the layers shaped like rings creating a cylinder, and then the PDMS layer from the tray caps of the other end. If you don’t think of the PDMS as a wall then the cell isn’t closed it’s more of a cup shape opening toward the PDMS.

Now let’s think about the shot glass example I mentioned earlier. Once the bottom of the glass is finished the printer starts working on the layers shaped like rings. During the peel and return process the pressure inside the ringed in area would become very different from the area outside. If the walls made by the rings are not thick enough a blowout will occur. This happens even though the final shot glass would have no closed cells.

Now consider a shot glass printed upside down with supports. First the supports print, then rings start printing, and last the bottom will print. The key here is that while the rings are printing there is no bottom printed yet trapping the resin in so the pressure can equalize, so there would be no blowouts. Instead of the cup shape the print would have a hollow cylinder shape at this point in the print.

The key to take from this is that for any hollow area in a print you want an escape path between the hollow part and the platform. Ideally this path will run from the part/s of the hollow area closest to the platform toward the platform, and be wide enough to allow pressure to equalize quickly.

As for why your parts came out sticky and had flaws all over them this seems to go with blowouts. They generally mess up all kinds of things on a print.

So now I think I see the shape you have there. The circles are deep cut to create a negative of a hollow cylinder. Try printing the pieces with the circles opening down toward the platform instead of up and away from the platform.

Also for parts that just stay sticky, if you don’t mind risking them getting a haze, you can rapid cure them by submerging them in water and putting them under UV light. In my cure box it can take from 30 mins to several hours to get rid of stickyness on most objects but some remain sticky even after that. However if I put a print in a clear container filled with water then put it in the cure box it cures anything to the point of not being sticky at all in 2 - 10 mins. The reason for this is oxygen actually impairs the curing process so putting the print in water allows the curing process to happen without the oxygen impairing it. I’m still trying to find a good route to preventing clouding with this process.

1 Like

Gotcha Rocus!

Didn’t think of the peel process creating this pressure build! you just taught me a few new things I should keep in mind when setting up the print! Thanks a lot for the help!

Curing the parts which are still sticky isn’t neccessary right now as I consider them waste, but I’ll keep in mind the trick you mention with the glass of water!

No problem. Figuring this stuff out has been a long painful process, it’s good to be able to help others through it.