top/bottom before shell

[ungutknut 4]

Hi,

 

is it possible to have top/bottom printed before shells?

 

There's "outer before inner wall", "infill before walls", but no "top/bottom before wall" which would be necessary to have a uniform printing order for the whole model. And because top/bottom often occurs at overhangs, these get printed in bad quality because the walls print first. At least that's my theory.

 

I'm currently on Cura 3,6 64bit on Win10 and Linux.

[Miech 0]

Good question. I was asking myself the same. Anyone?

[Slashee_the_Cow 265]

I don't think it's possible. There's a few reasons why it prints walls first anyway:

• Geometrical accuracy - if you print the top/bottom first (which is more likely to end up inaccurate, since it consists of more lines) and then the walls, the walls may be forced out of position by the top/bottom plastic which has likely already set (and has probably expanded a bit in the process). If you print the walls first, then the top/bottom is forced to stay within the walls.
• Visual consistency - due to the aforementioned problems with potential inaccuracy, it might make your walls out of alignment with each other where they touch top/bottom. There's also the possibility for small bits in a single layer to stick out, if a single top/bottom line didn't stay quite within its bounds.
• Overhangs - Most overhangs aren't printed with top/bottom at all, unless they're at a very shallow angle (which is probably going to need support anyway), with the exception of bridges. But the walls are still printed first because the top/bottom consists of many lines, which if unsupported is likely to sag under its own weight. The walls are lighter and more likely to stay in position (depending on how quickly your filament sets and the angle), and then they provide something for top/bottom to hang on to and spread the load.
• Strength - if some layers are printed walls first and some aren't, the walls aren't going to bond as well as if they're all printed first. This effect will be especially pronounced on layers just above or below the start of some top/bottom.