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Hollow outer shell using Cura 2.3.1: Looking for advice


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Posted · Hollow outer shell using Cura 2.3.1: Looking for advice

I'm having issues slicing a 3d model I created with openscad. My outer shells/walls are hollow. They should be 1.2mm thick, so with my nozzle of 0.4mm I was expecting a wall 3 lines thick. However, when I slice it with Cura 2.3.1 the outer wall becomes two 0.4mm shells with a 0.4mm gap between them. I've used meshlab to verify that there are no manifold issues with my stl. So I'm at a loss to understand why Cura 2.3.1 is slicing it in this way.

Some additional confusing things: I don't see this issue when I use other slicers such as slic3r or even with I use an older CuraEngine that is part of Repetier-host. These slicers create the outer walls as three 0.4mm lines as I was expecting.

Anyone have any ideas or having a similar issue??

Attached is a picture of Cura's layer output mid-way through the object where you can see my problem on the outer walls.

oshell-hollow-cura231.thumb.jpg.e42bb61439751fec115488e306ae619a.jpg

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    Posted (edited) · Hollow outer shell using Cura 2.3.1: Looking for advice

    I've seen similar issues and never gave it much thought - I assumed Cura is trying to preserve filament.

    But now that I think about it - and see your settings - I have to assume it's a bug.

    No solution, though, sorry.

    [edit]I think this is the same issue: https://github.com/Ultimaker/Cura/issues/1303 ?

    Edited by Guest
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    Posted · Hollow outer shell using Cura 2.3.1: Looking for advice

    Hi,

    Two thoughts.

    1) Try line width 0.38 instead of 0.4 and use multiples of that for shell width to get your 3 shells. SO 0.38x3=1.14mm shell. It might be enough to add the third shell.

    2) When I design with openSCAD, I have discovered that it is better to think of the nozzle as 0.41mm or 0.42mm and calculate wall widths that way. So 0.41*3=1.23mm. That way it covers any floating point rounding issues that Cura might have. I have had 0.4mm walls not slice but 0.41mm walls slice just fine as a single wall. Basically, add in a tolerance fudge factor to your designs and you should be fine.

    Also, the plastic will shrink a bit (PLA is roughly 0.1 or 0.2mm) when printed anyway, so you might want some tolerance added for that too if you need high dimensional accuracy. Depends on the plastic though.

    Hope this helps. Good luck! :) And welcome fellow openSCAD user! :p

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