Second layer floating in the air

[hapklaar]

Description of the bug

I just started using PrusaSlicer after being a Cura user for many years. After going through the learning curve, I think I should be able to use it now like a fairly advanced user.

From time to time I still have some very weird problems, this is one. I have a box with rounded edges on the bottom and PS refuses to support the overhang and I can't find out why. PS starts printing lines in mid air without any support being under it. I already tried setting the overhang threshold to ridiculously low values to see if it would make any difference, but alas.

Bottom layer:

second layer:

These are my support settings:

Project file & How to reproduce

Dim Bulb Tester Base.zip

Checklist of files included above

• Project file
• Screenshot

Version of PrusaSlicer

2.9.4

Operating system

Windows 11

Printer model

RatRig V-Core 3

[neophyl]

Because it can't. Its simple physics/geometry. Curves of that type are basically like nearly full overhangs, the problem is that they are too close to the bed, there isn't enough room to put support under there and have the required gap you have configured (0.2) between the support and your part.
Assuming you are printing at 0.2mm layer height then the first layer it can realistically support is the third layer. First layer of support 0.2+0.2 gap means only a layer above that ie 0.6mm will get support under it.
That's just for the Z height. You also have the X/Y part gap it also has to take into account. That pushes support out away from the layer too. So push it out and its not below the part to be supported.
Its why those curve types are not recommended for 3d printing in that orientation and a 45 degree chamfer is preferred (or a hybrid type).

You can play around with the z gap and layer heights but without soluble supports if you don't have the gap its going to be hard to remove them and you will end up sanding/post processing that area anyway. So just as much if not more work than not having the support. Basically just design a part for 3d printing in the first place.

[hapklaar]

Thanks for replying. I'll play around with it some more, however I found that Cura has no issue with it. It does put support under it and I also use a layer height of 0.2 there. Here are the first 2 layers seen from the bottom in Cura

Seems to me PS could do better? The second layer angles shown in PS are actually not there, it expands out gradually and Cura handles this correctly. I attached the original STL for reference.

Dim Bulb Tester Base.zip