too many retracts when slicing hollow object

Encouraged by Sublime's warrior princess print, I wanted to test slicing an object hollow with support in kisslicer.

My kids lost their yoyo, so I downloaded this from thingiverse.

When I slice it, after the solid layer prints on the bottom, I get an insane amount of destrings for the inside support. I actually stopped printing because I was afraid the extruder would just chew the filament up.

Attached is a screenshot of one of the layers.

I've used something close to the "normal" support from the Tantillus profiles:

; *** Support Settings ***
;
; support_name = Normal
; support_sheathe = 1
; support_density = 4
; support_inflate_mm = 0
; support_gap_mm = 1.25
; support_angle_deg = 75
; support_z_max_mm = -1
; sheathe_z_max_mm = -1
; raft_mode = 1
; prime_pillar_mode = 0
; raft_inflate_mm = 2

I tried sheathing, inflating support, but I didn't see any reductions in the retracts. What settings do you guys use for support for hollow objects?

Well a couple of things here.

Kisslicer does not generate support inside of an object as that is what the infill is for.

What you see in the picture of the paths is support but not support that should be there. That model is one of the worst I have ever looked at. It has all kinds of planes inside of it making shapes and voids that would impossible in reality. Since you are a capable modeller just quickly make a new version.

I tried to remove the inner structures and repair the model quickly and it was not possible in less time then it would have taken to redesign it.

Also that is not a shape I would ever print without infill. Domed tops like that need about 25% (or more) infill to turn out well unless you have lots of loops (10+).

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Thanks for the info on the support.

I thought you mentioned that you printed the warrior princess hollow, so I just assumed that the support would then take the place of the infill.

I never even thought about looking at the model, because it was generated from openscad and figured it would be a nice mesh. But you are correct, it's not a nice mesh. I guess the lesson learned today was to never assume!

No worries. Once I saw the picture of the paths I looked at the model in transparent view in Kisslicer but it did not show all the inner parts that were causing the issue. It was only when I started to try and repair the degenerate faces on the bottom in Blender that I found the inner parts. At first I thought oh this will be easy there is just a single plane across the entire model near the bottom of the nut traps and then found that there were far more planes inside that made no sense.

Also never trust anything that Openscad creates unless you make it yourself. It has to be one of the biggest sources of bad files in the world of 3D printing. There are a lot of people now that know how to generate good meshes with it but it requires fudging things a little. For example you can't have two faces on the exact same plane when performing a boolean. You need to move one object a few microns so the faces are out of plane and then it can figure out which face to use and not just leave holes or extra faces.

For the hollow printing I do it on artistic items more often than structural ones. I also pay close attention to domes and flat tops. If it has some domes I will add a perimeter loop or two and if it has a flat top larger than say 15mm x 15mm I will use infill to support it. I am not saying you need to follow these rules as you can print a large flat top without infill if your skin thickness is high enough that it can create a solid top surface on top of the broken bridge layers.

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver

Thanks for the tips about using support in KS.

I started with openscad because I was curious why others in the 3d printing community use it. A programmers' solid modeller sounded great, but I'm not sure that I fell in love.

It has a long way to go:

- the language is declarative. Fine with me, but it takes away a great deal of flexibility. (There is a project called OOML that wraps it in c++.)

- the gui is extremely primitive. It would be nice to at least have a measuring tool.

- exporting models is cumbersome. Not sure why this is not supported from within the language. (I'm currently using scripts to render multiple parts.)

- it is very time consuming to create things. I find myself spending a lot of time coming up with names for variables so later I can come back and be able to figure out how the design is put together.

- some of the most basic design tools like bevel or chamfer are missing and are near impossible to pull off.

- extremely slow. It takes 30 seconds to render an xy end similar to the one used on the tantillus, two unions and a handful of differences.

- but the one you mention above is the biggest: the underlying engine is incapable to decide if faces are coplanar, so every boolean operation has to be padded. This creates either broken geometry or a huge mess in the source files.

If you look at the scad file for the yoyo linked above, it's actually a pretty thought out model. It still comes out messed up. And to make something like this takes about five minutes in a 3d modelling application that has a gui.

I totally regret starting a large project with it. I wish I would've gone with freecad.