Cracks in prints after rinse and cure  

Since it was a calibration print, is the cracking worse/better between the objects to suggest maybe it was a layer time issue?

Resin was well mixed? Not been sitting on a shelf too long (e.g. starting to breakdown)?

How long was it in the US bath? Did you rinse with water after?

How long was the drying cycle in the CW1? How long was the cure cycle?

I'm wondering if either the wash medium (assuming you didn't do a water rinse) or the resin didn't care for the heat of the drying cycle. Try rinsing with water if you aren't and then let the parts air dry before curing and see if that helps. My other guess would be that the cure cycle is too long for this resin.

The cracking is more or less the same on all objects.

The resin was mixed well, and was a new unopened bottle. In theory it could have been a long time on a shelf at the shop. I haven't found a date code on it, but an extra close look may be in order.

The US bath may be of interest. It was set for 4 minutes, but when it was done, I was in the middle of draining and cleaning the vat. The objects was therefore left soaking for some time. I did give them a couple of minutes US bath in water afterwards.

I don't have the total time for drying. It took whatever time it takes to hit 40 deg C, and then it was kept there for 10 minutes. Curing i think was 8 or 9 minutes.

I have been searching the net, and it seems both the prolonged soaking in cleaner and the heat are the most likely candidates for the cracks. My next prints will get a short US clean immediately followed by a water rinse. Then air dry, possibly with a little compressor, but NO heat. And when curing has begun, I will take care of the vat.
If that doesn't help, I will suspect either the resin or the ResinAway cleaner (haven't tried either before this).

RE: Cracks in prints after rinse and cure

Posted by: @ejberg

I have been searching the net, and it seems both the prolonged soaking in cleaner and the heat are the most likely candidates for the cracks. My next prints will get a short US clean immediately followed by a water rinse. Then air dry, possibly with a little compressor, but NO heat. And when curing has begun, I will take care of the vat.
If that doesn't help, I will suspect either the resin or the ResinAway cleaner (haven't tried either before this). 

Might also try multiple shorter cures (e.g. 2 5 minutes rather than 1 10) with a pause between as the cure process generates heat too.

Posted by: @gnat

Might also try multiple shorter cures (e.g. 2 5 minutes rather than 1 10) with a pause between as the cure process generates heat too.

Thanks. I will keep that in mind the next time I print something (next weekend I'd guess).

After a new test run, I am losing faith in this particular resin. Switching from ResinAway to plain IPA, no ultrasonic bath and no hot air drying, prints are not improving. Furthermore, the rest of the resin in the vat started to solidify at the surface. Either there is something REALLY wrong with this bottle of resin, or I am having UV light in my ceiling LED lamps 😲

I have now ordered a bottle of the new Prusament Rich Black resin, hoping that will be the end of all my problems.

Monocure tech support?

Does Monocure tech support have anything to say about the cracks?

Posted by: @mikeh-2

Does Monocure tech support have anything to say about the cracks?

I haven't tried to contact them, but in their FAQ I found this:

if you give the resin a good shake and see particles in the resin then it is time to dispose of it

And I do see small particles in the resin. It is like the black pigment has clumped up in small clusters and just float around in semi-transparent resin.

But that is all history now. I have received Prusas new rich black, and what a difference. First try and it works perfectly:

And here is a comparison between Prusament rich black (left) and Monocure 3D Rapid Black (right):

Old resin?

How long have you had the Monocure resin?  I have some of their resin (unused) that is probably 2+ years old.  Probably not not much that is worth using any longer 😲 

I only had it for 9 months (got it last christmas).

I have two theories. Either this bottle has been rather old when sold, or Monocure Rapid resin isn't compatible with the higher UV output of Prusa SL1S. It seems Monocure has both standard and rapid resin, where the latter is designed to be fast curing in low-power 3D printers. Perhaps SL1S is simply too much for it?

Final verdict is that it must be that bottle of Monocure Rapid Black that is too old. I've just tested/calibrated a bottle of Monocure Rapid Clear, and it worked fine (settings ended up being 2.8s / 20s at 50µm).

The black bottle was produced in march 2019 and sold november or december 2020 (and then given to me for christmas). That is an awful long time sitting on a shelf before getting sold.

RE: Cracks in prints after rinse and cure

Whats the surface finish like with the prusament rich black for you? Mine always feels like it is never fully cured, the surface feels almost rubbery/ silky compared to the previous prusa resin which had a matt finish

RE: Cracks in prints after rinse and cure

Posted by: @matty

Whats the surface finish like with the prusament rich black for you?

The surface finish looks quite normal to me. Perhaps it has a little more satin gloss than other resins.

To my surprise it seems much more flexible than other resin prints. I can still break it of course, but it isn't as brittle as e.g. the old Prusa Tough Orange or Azure Blue.

RE: Cracks in prints after rinse and cure

After curing it for over 30 minutes to see if it had any impact to the surface finish  which it didn't, I think you are right that the prints are like a satin finish, most of my other resins including the older prusa tough resin have a Matt feel to them