Isolated islands of material in thin air

[ChristianSi]

Slic3r sometimes sets isolated islands of material into thin air, when there is nothing under them and no connection to the rest of the layer to support them.

The following screenshots show this problem at layers 95, 173, 174, 267. That's from the Yoda bust http://www.thingiverse.com/download:46150 sliced with the following settings:

; generated by Slic3r 0.9.9
; layer_height = 0.2
; perimeters = 3
; top_solid_layers = 3
; bottom_solid_layers = 3
; fill_density = 0.35
; nozzle_diameter = 0.5
; filament_diameter = 2.88
; extrusion_multiplier = 1
; perimeters extrusion width = 0.80mm
; infill extrusion width = 0.80mm
; solid infill extrusion width = 0.80mm
; top infill extrusion width = 0.80mm
; first layer extrusion width = 0.80mm

[kefir-]

Did you enable support?

[ChristianSi]

No. I know that it can be argued that Slic3r simply does its job by faithfully rendering what's in the STL, even if that results in unprintable islands (when not using support). True enough, but as I understand Alessandro it's still not supposed to do that.

In my opinion it would be better if Slic3r simply omitted these unprintable islands, even if that results in a less accurate rendering of the STL. Alternatively, it could at least emit a warning along the lines of "You need to enable support to correctly print this file".

[jfpion]

i've got the same sometime
stl : http://jean.francois.pion.free.fr/upperfan.stl
gcode : http://jean.francois.pion.free.fr/upperfan_slic3r.gcode

with this results:

look like it is connected to thin wall as it is at the verge of a sharp edge

[jfpion]

an another example

[lordofhyphens]

At best I can see a warning if unsupported islands are generated may be warranted.

I prefer to think that our users aren't idiots and if they want to generate a slicing pattern with unsupported pieces, they know what they are doing and can live with the consequences. Might be able to repurpose the support-generation gcode and fire off a UI warning if the model would get support added (using autodetection, etc).

Of course we'd also want a method (probably in Preferences) to turn such things off.