Help with Flex v2

I sent this inquiry to Support, but since it’s a weekend I’m hoping someone with more experience than I have using flexible resins might be able to offer some pointers.

I’m having trouble with a specific print in Flex v2 resin:

(photo above from second-last attempt)

It suffers increasing layer shifting as you get further from the build platform, along with eventual delamination. Also some of the interior support structures fail, although I’ve managed to mostly mitigate that issue.

I’ve made four attempts, each time enlarging the contact point sizes and adding in extra supports manually where it looked like they were needed. Here are photos of my latest attempt.

Here’s the corresponding .form file, and screenshots:

(screenshots above from latest attempt)

I generated the lattice using default 1.5mm contacts, then threw in a ton more of them by hand, as well as several larger 2.5mm ones (the larger dots). The print was done using the latest Preform and firmware.

If you’re interested, here are more photos of the previous attempt.

Unfortunately due to the size and shape of my part, and the need for it to be a single print (it’s a custom remote control sleeve), I can’t reduce the angle or height of the model (I realize this is why Formlabs recommends shallower angles and shorter parts). I can live with a bit of layer shifting but need the print to finish so I don’t end up with a corner missing:

I had great initial success for very small models like these ~1cm diameter tires but more recent attempts at larger models are seeing repeated failures as above.

Ideas would be greatly appreciated!

(ps. Unfortunately I don’t yet have any Flexible 80A or Elastic resin to see if that magically solves it)
(pps. These are printed on my Form 3; I haven’t tried them on the Form 2 as I don’t have many spare tanks and assumed LFS is the way to go for flexible)

Interesting. I know a model like this in the Form 2 would be challenging because of the shear forces during peel but thought the Form 3 would handle large flex prints like this better.

Does it fit ok the build platform vertically? If it does, might be something to try such that all forces are in tension only…but it doesn’t look like it would fit given your images.

Formlabs support told me at some point that there’s a general rule of thumb for height on elastic parts for the Form 2. This makes sense, as once the height exceeds that, you start getting significant problems due to hysteresis during the peel since your part deforms and doesn’t bounce back to the right spot. Again, thought it would be better with LFS and the elimination of shear. Even though that was for elastic I’m sure it also applies to flex. Even though the F3 is peeling in tension, depending on the orientation of your part you might still get shear forces which could deform the part and prevent it from registering properly at the next layer. Maybe add some more supports all around the sides to help keep it’s shape?

I haven’t yet done anything this thin and tall with flexible, but I’ve done a fair amount of prints with both flex and elastic…including some larger, bulkier parts. In all instances I’ve noticed much better results on the F3, specifically around cupping, support sizes, and a reduction in deformation during peel.

I also know that flex v2 gets really thick and starts to separate if left for a long time. You may want to try scraping thoroughly mixing the resin in your tank. If it’s left in there a while, at least on my old F2, it would cloud the base and you’d have to gently scrap that off to get better prints. The built in mixer in the f2 wasn’t really good enough to mix that well (same thing happens with rigid resin).

Anyway not sure if any of this helps, buy good luck! Worst case, you can split the part in two I guess.

Thanks for the suggestions.

I’m up to 2mm contacts and 1.25 density, with extra touchpoints everywhere I could fit them. Added a ton of supports around the sides. I think this print could work if I were able to generate a more robust and laterally reinforced support structure. The stock lattice out of Preform just seems too wimpy for this resin. I might try out some 3rd party tools for that or even model something myself (ugh).

Here’s an example of how the supports themselves are failing:

One of my issues is that increasing the contact size doesn’t seem to result in a corresponding increase in the opposite points at the base of the internal support. That’s one straightforward thing Formlabs could improve (at least for this resin).

I don’t think the part would fit straight vertical, and alas I want to keep it as a single unit.

That looks pretty crazy. It almost looks as if those areas aren’t separating from the film during the peel.

I just printed some small parts in flex and they came our really great at 1mm touch points.

Are you checking your tank and filtering the resin after these failures?

Yes, small parts are fine. The tires came out perfect with 0.5mm contacts (along with a couple 0.85mm ones near the first layers). I don’t think the failures flaked - they left nice, clean pancakes behind and I don’t see any contamination in the resin in the tank, but it’s a good suggestion and I’ll try filtering before the next attempt for good measure.

Given how the problem exacerbates the further you get from the platform, I think it’s mainly due to the height and insufficient support structure. From what I’ve been seeing I’m convinced Preform could use some “smarts” to better tailor the lattice for flexible prints. Specifically:

  • Larger contact points at the base of internal supports - ideally proportional to the contact size at the other end. It’s no good putting a 2mm contact on one end if there’s nothing more than a couple say ~0.8mm contacts providing it’s fixture at the other end.

  • More lateral bracing. I recognize peel “hysteresis” can’t be eliminated, but I suspect a more robust structure would help significantly. (I’m actually envisioning something like shear walls for my custom attempt).

  • Thicker columns. I think an early version of Preform (in the Form 1 days) used conical columns, I’d love to try something like that for this resin.

I’ve also observed contact points nearer the build platform can afford to be smaller, with larger contacts necessitated as you get further away.

Loads of opportunity for Preform to improve with regard to this.

I, too, was really hoping LFS would let me push the envelope more with this kind of material.

Anyway, here’s that last result after some rough sanding:

I agree more lateral support would probably help.

I’d at least start a ticket with FL support so that it shows up on their radar internally and potentially promotes this for the next revision of Preform.

I feel your pain though. Flex and Elastic can sometimes be so hard to work with…I printed this huge Elastic hinge last year on the F2 which failed so many times until I got it right…and just today I pushed my luck and printed something with really thin walls with no supports and thus the ultra thin wall sections deformed. Guess I deserve it haha.

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