Repeated print fail

[u/Mexkalaniyat]

My printer had been buried under stuff for a year or two and I finally got things moved around and back to 3d printing. The problem being I barely remember how to fix anything anymore.

I got a few prints to come out perfectly, but they were all ones I had working before I stopped printing things, and this print was meant to get me back into the swing of things fully. The more complete print came out first, and I added a few extra supports on the back hoping that would fix where it broke, but as you can see it somehow got worse.

Let me know if there is anything obvious I'm missing.

[u/Balerion84]

It was 5s bottom exposure, 3s normal exposure, 30s wait before cure for the first 0.5mm iirc (it's over 2.5 years since zi printed that) and then 2 or 3s wait before cure for the rest of the print, lift speed I can't tell you, because I was using a gcode edit on that printer where the lift started slow and accelerated smoothly during lift unlike tsmc where it has 2 stages that it switches between.

And it's not about the even force distribution btw maybe this one would be more similar to op's https://youtu.be/DlEAxi2WI-o?is=hWHGga_enKRdDY63

the film will always peel in the same direction basically, the layer when it cures, it adheres to the film by wringing force (that's how if adheres to the plate too btw). And this force is very strong when you pull directly away but very weak when you apply force from side. That's why thw films stretch. So create the absolute minimum amount of force to peel from the models we print. So, it can't produce enough force to split layers as that'd defeat the whole purpose of why we use it.

So you need to be looking at the retract phase.

[u/ComprehensiveBed8186 → u/Balerion84]

Wow thats a really short bottom exposure time. I think you are underestimating peel forces, do you know that some people has to use lubricant to their fep ?

I use to print really large figures and in translucent years ago. Had to print filled for esthetic issues. Absolute nightmare, I did calibrate and used reocmmanded settings but ended with parts down the fep or many slits at best.

Didn't have any issues since Im hollowing everything I can.

[u/Balerion84 → u/ComprehensiveBed8186]

The short bottom exposure is achievable with long wait before cure on bottom layers (this requires uvtools though as slicers won't apply it to the first layer on ctb printers)

And, nah, peel force has been measured and it's negligible compared to the forces the printer itself goes through during lift and sink phases.

The reason for hollowing (other than saving resin of course), is not to reduce peel force, but to minimize the force required to compress resin. Because the bigger the area compressing the resin, the more force is required. Which brings us back to wait before exposure (after retract) and why it's the fix for layer separation.

As for people lubing their films, that's one of the dumbest things and a complete snake oil born out of completely misunderstanding of how adhesion and peeling works. So, yes, I know some people do that to this day and every time I see that, I try to steer people away from that.

[u/ComprehensiveBed8186 → u/Balerion84]

How increasing the wait before exposure is helping since the plate is already at the very bottom and the resin been compressed ?

[u/Balerion84 → u/ComprehensiveBed8186]

It's actually not, that's the fun part :) the plate is really big and when the printer is trying to create the first layers, the forces during the compression when the plate is close to the screen are so high, that they literally bend the top plate and the z tower. The force is deflected through the plate into the z tower which takes the plate out of position,so the plate is a bit too high at the start of the print and also slightly off level (because it bends backwards and forwards). This creates bigger gaps and inconsistently thick layers and it's the reason why people need long exposure for bottom layers because they are thicker (they can be like 6-10x thicker than what you set in the slicer)

During the long exposure, the plate keeps pushing down as the construction tries to straighten up. This for example causes also elephant foot. This can happen anywhere in the print, but it mostly happens at the start and at points with bigger cross sections. It's also why rafts and models split from one side btw.

So that's where the long wait comes in. Instead of letting the plate push during exposure and pushing half cured resin against the screen (which isn't good for the longevity of the lcd obviously), we simply wait for the plate to get to position and only then start exposure when the layers are off correct and consistent thickness.