tl;dr although Formlabs say they did not change the print settings for Clear V4, this clearly is not true as it is impossible to print parts with Clear V4 @ 0.05mm layers (failure rate >90%) but when pouring V4 into an older V2 cartridge everything comes out fine. Bug in PreForm?! tl;dr
Backstory:
My name is Mikus and I am engineer at a startup. We are developing a device which we produce in low volumes using Form 2. The main body of the device is a 2.5mm thin shell from two parts and is 174mm in height - this meant that to optimize the Form 2 print time and efficiency we need to print the parts straight onto bed vertically. This way we can fit 2 cases at the same time cutting down time from ~36h to 25h. Since there are overhangs supports are needed, but since there is no room for PreForm generated supports (since they require raft) we had no other choice as to incorporate our own custom supports which we dialed in trough trial and error but they came out perfect. We printed from Clear resin (V2 at the time) at 0.05mm layer height. We have printed around 10 sets of these parts but then we ran out of Clear V2 and had to order Clear V4.
As Formlabs has stated, the formulation for V2 and V4 is basically identical so we did not expect any issues. At the same time new firmware and Preform 2.14 was released. As soon as we received V4 and started printing, it was obvious that something was not working as it is supposed to⊠After first few layers, parts and some supports just broke loose and were delaminating, resulting in a ruined part at best and ruined resin/tank at worst without a part in one piece. You can see a small timeline of how the parts look like and how the V4 performed on the same identical parts in this Google Photos gallery. The results speak for themselves. You can see each parts print settings and resin captioned.
At first I thought that there were some issues with new firmware/PreForm and upon checking out forums it seemed like I wasnât the only one having quality issues with the new firmware/Preform. So I downgraded back to the older firmware and Preform 2.13.1 but that did not help as the issue remained. We also tried to lower the Z platform for the first layer by -0.2mm with no luck - first few layers come out perfectly fine - remaining ones barely holding on or delaminated entirely.
We have had Support ticket open for 2 weeks with literally no suggestions just blaming our custom supports or âbrokenâ STLâs. So I tried to take the investigation to myself to understand what the f*ck is going on here, since our production has been halted for literally 2 weeks with no solutions in sight.
Investigation:
To diagnose what is the potential issue here, I cut a small piece off our large part to have a part that actually represents our use case as well as a small rook, similar to what Formlabs prints for example parts to make sure that the issue is not in our part not having appropriate contact surface with build plate.
So I printed the two parts at 0.05mm (since this the the resolution we need) in different materials and print settings since changing PreForm/Firmware did not change anything visible. This way I wanted to narrow issue to either 1) material 2)print settings or 3)model issues (although we previously had no issues, it could be a factor).
These are the two parts:
Results:
Gray V3 printed out perfectly fine - no issues here so I did not even bother to put a picture up.
Things however get interesting when we come to Clear V2 printed with V2 settings and Clear V4 printed with V4 settings. V2 came out perfect and V4 failed. So I printed one more set with Clear V4 but poured in an empty V2 cartridge and using V2 settings - and guess what, part came out exactly the same as Clear V2 parts. See for yourself:
(parts are updside down)
I did not test V2 with V4 settings since we are really behind our deadlines in our production⊠But considering these results it is pretty obvious that there are STILL issues with V4 print settings and they ARE NOT identical to V2 despite what @Frew said here and here.
I also read there was a bug with V4 resin settings that is supposedly fixed in Preform 2.14 but that is irrelevant since this was the same exact issue that also occoured when I used Preform 2.14.
On top of that there was a new thread created on the same issue here which states that guy is having issues printing V4 at 0.05mm even with supports. This correlates with my issue.
As for technical information: Preform 2.13.1 / Formware rc-1.14.21-154 / .FORM file
For now we will just pour V4 in our remaining single V2 cartridge since we just threw out remaining ones just a week ago but this is not acceptable for a long term solution! Hopefully this will be fixed soon 
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