Please document behavior of first 0.8 mm CLEARLY

Dear Formlabs team,

we had to learn the hard way, that:

  • The first 0.8 mm of any print will always be print with 100 µm layer height (to aid adhesion I would assume), ignoring any other setting.
  • The profile / laser scan path of layer 7 is copied to layers 1-6, ignoring ANY features which reside in these first 0.6 mm. BTW: This makes printing directly on the build surface so much less attractive!

Please do document this behaviour somewhere obvious! Imho this is important to know when preparing any print, which does use your new “on build platform” supports feature or is printed directly on the build platform. TY.


Part dark blue with light blue laser lines on top, ignoring the arrow feature:

PS: I am not sure, whether I should report this behaviour as a bug or not. When printing something on the Build platform directly, it should not be altered at all tbh!

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I know it is stated in a few places that the first 0.5mm is compressed by the z axis to ensure it adheres to the build platform

Thanks for the feedback. Because the part is compressed into the tank, though, I think you’ll find that if you print features like that arrow with earlier versions of PreForm, the arrow still will barely come out. On the flip side, this feature makes it possible for you to print parts that for various reasons aren’t quite planar (such as textured parts or parts that in their STL file are almost but not quite axis-aligned) directly on the build platform, without having surprise issues with adhesion.

Dont get me wrong, I understand the motivation behind this very clearly. And the above example is certainly nothing I was expecting to come out of the printer as designed (it was part of a bigger test print with various orientations / support options). But in other cases this “feature” of copy/pasting layer 7 down is quite hindering and good to be known of.

This is not a feature request in terms of “do that in another way” but rather “please tell more clearly, what the software is actually doing”.

You are talking about the hardware pushing the build plattform ~ 0.5 mm into the resin tank with Z=0. I am talking about the software modifying the printed layers to achieve better / more consistent adhesion.


Thanks for the reply. Documentation aside, would it be less surprising or look more intentional if the fill were capped by a blue polygon so you didn’t see laser paths floating in free space?

Imho seeing the individual laser lines is very helpful in a lot of cases (fine features, thin parts) and disposing of this view would do more harm than good. So no, a filled polygon would not be any better from my point of view.


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By the way, while I realize it’s not in the UI explicitly, we did mention it in the PreForm 2.18 release notes “Early layer unioning improves adherence when printing without a raft.”

So this is a new feature? … well… perhaps add an opt-out in the next version under the advanced support options? Just as an idea…

Still, putting this feature into one of the release notes with a one-liner is not the same as communicating such behaviour clearly in one of your documentations.

Dear Ben,

another question regarding the same topic:
Your (Formlabs) sample parts (these ones: are printed on the build platform directly with methods to hide the first layer defects to some part (i.e. 45° fase on the bottom for instance). Do these methods still work with Preform 2.18? For example, a 45° fase will be straightened out for the first 0.7 mm, which is quite significant and striking. How do you solve these issues for your sample parts? By not using PreForm 2.18?

TY and BR,

They should. That first 0.7 mm will be almost if not entirely eaten by compression.

Nice to see you guys working to give us more support options. I made a related suggestion over here regarding layer unioning: Fine tuning Early layer unioning height

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