Bug? in 1.5 B2.20 and earlier

[OldRick]

I'm getting the darndest reproducible error with KS on an important product that I manufacture on my Ultimaker 2.

I need to use KS because it is the only slicer that allows me to hide the path start/ends by placing them in an internal curve, but it is giving me odd results: reproducible blivets that protrude near the top and bottom of the piece. (see picture)



The image shows several of my tests - the one on the left is from Cura, the rest are KS. Each of the KS pieces has three distinct blobs where the head pauses briefly and squirts a blob. Also near the top of the piece there are slight bulges at the start/end points, and near the bottom in the first half-dozen layers there are also blobs being created.

The blobs are not in the model, and occur with versions of KS beta back to the Sept 14 version. The model does not show any errors that could cause the issue, and nothing odd is visible in the Paths view in KS.

Even changing the layer height still produces the blobs in the same places. I've tried every combination of settings I can think of, and spent the last two days trying to get rid of the raspberries - when I change settings, they sometimes move around a bit, but they don't go away.

I've attached the .stl and the gcode showing my settings in the hope that someone can help (unzip the files after download). Bug or Not?
https://dl.dropboxusercontent.com/u/338 ... ng.stl.zip
https://dl.dropboxusercontent.com/u/338 ... .gcode.zip

[Dreide]

The problems seem to correlate with layers that have small pieces of crowning in it, although I would have no idea how crowning could cause the problem, especially given that the crowning is printed after the perimeters. But maybe switching off crowning all together or at least using a much higher crowning threshold would help.
The problematic layers are also rather small, so not sufficiently cooled down material can be pressed more easily against the perimeters in case there is any overextrusion. Sometimes, KISSlicer does weird things, like in this layer: the inner loops are printed almost on top of each other, which is weird enough already, but KISSlicer still adds crowning paths. All the excess material has to go somewhere...

[OldRick]

Interesting thought - I'll try turning off crowning. If nothing else, perhaps it might help reduce the bulging ring that KS creates where the interior changes from 50% fill at the bottom to open space inside a 2.5mm wall.

[OldRick]

No - no improvement from crowning threshold set to 6mm. It did remove an artifact caused by repeated blobs one layer under the skin, causing a vertical scar-like bulge.

[IceMan]

Just printed your STL file and can't really see any of your problems in the print itself.
This was printed on an i3 using Marlin firmware and sliced with KS 2.20 x64 Pro
0.2 layer height
3 loops per to inside
20% fill
ABS

[frozen.rabbit]

You turn off Crowning by setting it to -1, not a larger value.

[OldRick]

I tried both directions on crowning: any value left a shallow "seam" where the internal crowns outdent the surface, and with no crowning at all the "seams" went away. No other effect.

I've finally stopped trying to make these pieces look molded, and gone with .48 layer height. To me it looks 3D printed, but to others, it gives better grip...

[OldRick]

Just printed your STL file and can't really see any of your problems in the print itself.
This was printed on an i3 using Marlin firmware and sliced with KS 2.20 x64 Pro
0.2 layer height
3 loops per to inside
20% fill
ABS

Yeah - at .2mm-2.8mm, the blobs don't show up on my Ultimaker 2 at all, only at thicker layer heights. I've concluded that I'm at the limits of the UM2 extruder and n.5mm nozzle with anything thicker. I'm anxiously waiting for an on-order direct-drive printer to see if it handles thick layers better.