Automatic threshold setting fails to create support when needed

[harriv]

Support is not generated when needed when using automatic settings.

Files:

https://drive.google.com/folderview?id=0Bw1VY8X1WZhdbTNaMVlnWDdlMnM&usp=sharing

Command line: C:\Program Files\Repetier-Host\Slic3r-1.1.3\slic3r.exe --load "C:\Documents and Settings\harriv\Local Settings\Application Data\RepetierHost\slic3r.ini" --print-center 75,74 -o "C:\Documents and Settings\harriv\Local Settings\Application Data\RepetierHost\composition.gcode" "C:\Documents and Settings\harriv\Local Settings\Application Data\RepetierHost\composition.obj"

Using Slic3r 1.1.3 32 bit on Windows XP.

[harriv]

#2072 is similar.

[hyperair]

Have you tried printing it? It might actually print the overhang fine, depending on your perimeter extrusion width to layer height ratio.

I think it's unrelated to #2072, because #2072 is about elevated islands, i.e. where the first layer of that section doesn't start on the layer 0.

[hyperair]

Hmm, this is weird. I just looked at Slic3r 1.1.4's code for automatic overhangs, and it looks like this:

                    $diff = diff(
                        [ map $_->p, @{$layerm->slices} ],
                        offset([ map @$_, @{$lower_layer->slices} ], +$fw*2),
                    );

Shouldn't that be $fw/2 instead of $fw*2?

[harriv]

@hyperair No, I didn't try to print it this way, because it looks so unstable. Center of gravity is so far away from support surface, which is very tiny..

[hyperair]

It's a little far overhung, but if it was a 45° incline, that model would actually print fine with --support-material-enforce-layers=10. Basically enforce support on the first 10 layers to ensure a decently sized footprint on the build platform. It doesn't matter that it looks unstable -- it's meant to stick to the platform for the entire duration of the build.

[harriv]

Yes, of course it would print if the support is manually forced. I think this is special case which has not been considered when designing the current automatic support generation.

[hyperair]

But that's what the enforce-layers option is meant for -- if your print isn't capable of getting an appropriate first layer stuck to the bottom. This could be just as easily mitigated with a brim, I think.