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over extrusion only at top infill?

Posted by o_lampe 
over extrusion only at top infill?
April 03, 2017 03:49PM
I've tested a volcano hotend with 0.8mm nozzle for the first time and I couldn't fix one problem:
The top infill is over extruded while perimeters are perfect. So it can't be e-steps related.

I've set all extrusion width to 0.8mm and even tried to set solid & top infill to 180% because the first layer looks perfect with 180%, but it's always over extruded.
I haven't seen this with the 0.4mm nozzle.

Is it because of the lower back pressure in the melt zone?

Maybe I should mention, that I use " infill every x layers" so the infill prints every other layer. But the final three layers are all printed separately.

Edited 2 time(s). Last edit at 04/03/2017 03:58PM by o_lampe.
Re: over extrusion only at top infill?
April 03, 2017 06:56PM
I have this EXACT same problem. All of my other extrusion widths come out perfectly, save for the solid infill layers. They seem to over-extrude.

Edited 1 time(s). Last edit at 04/03/2017 06:56PM by MrBaz.
Re: over extrusion only at top infill?
April 04, 2017 04:57AM
I updated to new 1.34 Prusa edition and it seemed to improve a bit.
At least the track width is wider than before and seems to match extrusion width.
I'll try different extrusion width's and report back.
Re: over extrusion only at top infill?
April 04, 2017 08:52AM
It is difficult to see on the photo, but it looks like there are only 3 lines of extrusion around the wall? If so, then it is a "thin wall" - i.e. a wall that is thinner than [extrusion width]*(2*[number or perimeters]+1). In that case there will be gaps if the wall thickness is not an exact multiple of the extrusion thickness and you do not have "gap fill" and/or "detect thin walls" checked where available - though AFAIK there is a bug in the gap-fill algorithm used by Slic3r (it grossly over-extrudes) so that won't work.

You can fix the issue by setting the perimeter extrusion width(s) so they are very slightly less than an exact division of the wall thickness. You could possibly also reduce the number of perimeters so that the gap between the perimeters is larger than the infill extrusion width.

Re: over extrusion only at top infill?
April 04, 2017 09:51AM
The Prusa / slic3r team seems to have debugged a few issues, including the gap-fill.
I still had a single line protruding above the others on the top layer ( with 0.4mm nozzle ) but not as bad as with the infamous V1.29

The left is sliced with V1.33 . It seems the nozzle has to shove through the fresh filament.
The right has the same parameters, but there are fewer and wider tracks.

Both infills are bulging out, but the right a lot less.

Edited 1 time(s). Last edit at 04/04/2017 10:06AM by o_lampe.
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