this post was submitted on 03 Dec 2024
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[Resin Printing] Any tests for finding the minimum lift height? (self.3dprinting)
submitted 1 day ago by papalonian to c/3dprinting
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Something I've noticed when watching my resin printer work is that a lot of time is spent every later lifting the plate well after I hear the model unstick from the FEP.

It's not a huge deal on smaller prints, especially ones that can be printed with "vroom" settings, but on larger models that are being printed at 1-2mm/s lift speed, several hours are spent just waving the model in the air for no reason...

I had the idea of making a test model that is essentially an intentional suction cup in the center of the plate (where FEP stretch is most prominent and required lift distance should be highest). I would print this model multiple times, with slightly lower lift heights each iteration, until it fails to release from the FEP. I'd add a safety margin and set my raise height to that...

Does anyone see any fault in my logic, or know of a better method of achieving what I'm after?

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[–] NickKnight 1 points 1 day ago (1 children)

I can see your logic and i can see Fribbtastic's objections. I am not sure immerse in a liquid a suction cup will be necessary. I would start out with a 20mm cube. A pure flat surface right in the middle of the filament where you're going to get the most flex of the film.

I would sincerely consider giving your film 50% slack for eventual failure and loosening but your idea is sound. I do think commenter is right though that this would be something to redo on every single film replacement AND every single resin you use.

I'd genuinely be curious to see time saved VS used up to dial it in.

[–] papalonian 1 points 22 hours ago

Time saved vs used is a pretty good argument against.

My previous printer (Anycubic Mono 6k) allowed you to change lift height and speed on the printer during a print, so I could just lower it until just above hearing the separation. My current printer (Saturn 3) doesn't have this capability, so it would have to be multiple prints, which would take a couple hours.

What might be a better solution, is to do a similar test, again with "worst case scenario" (ie a cup with no suction cup release hole, or a very small one), increase the result by a large margin of error, and go with that until I need to replace the FEP or prints start failing.

[–] Fribbtastic 1 points 1 day ago (1 children)

I can think of two problems:

First, not every Release Film is the same. You are talking specifically of FEP which is mostly used to describe the Release film and was commonly used for that but is the material that the Release film is made from. There are different types like the already mentioned FEP but also nFEP, PFA, ACF and probably others as well. Each of those materials has a different rigidity which would mean that they peel away from the Model sooner or later. According to this, FEP is much more flexible than PFA or ACF.

Second, the durability of the Release Film. Over time, the Release film will wear out and need to be replaced. They could become more flexible the more you use them. Cutting it too close could mean that your models will fail from one print to another.

Some other thoughts:

  • How much the Release film flexes could also depend on the surface area being printed. More surface area could mean that the layer is sticking to the release film longer
  • The same would apply to the Exposure rate because higher exposure rates make your layers stick more, including to your Release film
  • Assembly also plays a role in this. Since you need to replace the Release film at some point, you could add more or less "slack" on the film which would throw off your previous test massively.

While I like the idea, I think it would signal a false sense of confidence in your printer because if you "dial in" your lift distance and the model then fails, people could start looking in the completely wrong direction to fix a problem. I mean, with that many variables to consider, people still download the validation matrix without adjusting their bottom and transition layers based on the description and then ask why their exposure test doesn't work.

[–] papalonian 1 points 21 hours ago

All very good points. I think if I want to continue entertaining this idea I need to adjust my sights to a more general number than anything exact. Another user pointed out that time spent testing vs time saved would be a pretty close cut. I might devise a test to find a general minimum, increase it by a fair margin, and call it close enough.