Why is there a minimum distance between walls?


i try to understand, why nearby walls melt together. Is there a heat effect at the borders of the walls that the resin between thes walls melt together`? The minimum distance in the design guidelines is 0.5 mm, i had successfull prints with 0.3 mm. But i’m trying to understand why the clearence can’t be less.

Best Regards

The 0,5mm min guideline is a conservative value. The Formlabs design rules are general and you may achieve better values. I have read a couple of times (in this forum) that Black seems to provide a very good resultion.
You will have to do some testing.
Presume the resin hardens once the photointiator recieves a critical dosis to start the a localized polymerisation. A dosis is spread over the laser spot width. The amplitude of the laser point can be envisioned as a gaussian curve. So depending on the amplitude and the beam waist diameter there will be an effective spot size. Apparently the Form2 width size in 140µm, measured from half ampliture to half amplitude.
According to Form2 in-house testing there is a feature resolution of 150µm.
All in all this may mean with the 25µm setting and optimal positioning of the walls (I am not sure if that means tiliting 45° oder not, for example) there may be an optimum minimum wall difference.
Make a line & spaces test of your own and show us the results.
Another way of testing resolution, which I haven’t seen done with a 3D-printer, is with a Siemens star. This lets you see the minium wall resolution accross all directions on a planar surface. This is used for measuring the resolution of a lens - ccd system. I have used it for measureing microstructure resolution (with advanced x-ray lithography) and can recommend it here as well.
Based on my experience I would expect 0,3mm minimum distance possible. However, the resin is viscous and capillary action will clog these up. I brush fine features with IPA during my rinse to brush out resin before the post-cure.
I don’t think there is a “heat effect” that you mention in your assumption.

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There’s other things that can affect it as well–at the very least, the pigment in the resin will bounce the light within the resin and cure a bit more than usual(so White and Grey will have that issue the most). Clear won’t have as much of an issue with that problem since it doesn’t have any pigment. Besides that, if the laser beam is not parallel to the walls being printed, then the laser itself will extend beyond the current layer and cure extra material between those surfaces.

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