Blobs, Blobs everywhere !

Hello,

I'm facing an annoying problem, may be two but I think they are linked.
1- The top layer of my part is ugly. There are strings everywhere and mainly, the plastic is pushed by the extruder like if there was too much plastic extruded... Even in some locations, I can see the nozzle trajectory in the plastic

I though that the problem was linked to the parameter in Slicer: "Top infill" in advanced parameters. However, I have tried the range 0.1-0.4 without success. Here is a picture of an example:




And then, on a 2nd example, a little cylinder, the last layers are completely crazy, the plastic is pushed outside the perimeter. Here is a picture:



For that, I have tried to disable "Retract only when crossing perimeter" in Slicer without a change. I tried that because this plastic blob is appearing exactly when the extruder is retracting.

Finally, I think these two problems are related because fundamentally, it's like extruding too much plastic just on the last layers !


Do you have some ideas to solve that ?


Thank you for your time !


My config:
3d printer: K8200 with homemade extruder + E3D V6 3mm
Plastic: green PLA (really old)
Slicer: Slic3r 1.1.7
Software: Repetier 1.0.6

Edited 1 time(s). Last edit at 07/10/2015 10:14AM by Lmecano.

If your seeing scores on the print as the extruder travels across it would seem your print bed is too high, which would catch the top layer and push to wall out as it moves. Have you got a Z hop set?

I think you've diagnosed your own problem - you're over extruding. The reprap wiki has some excellent advice for fine-tuning e-steps per mm to combat this. [reprap.org]

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[3DKarma.com] - suppliers of quality, affordable 3D printer kits and filament for the UK market.

I noticed that Slic§r has problems getting the extrusion right in some cases if the extrusion width is not defined.
When I leave all to the default "0" ther is no real problem in 90% of the prints, but for the rest it is a lost print due one of the follwing:
1) not enough filament for infill or top layer, but in return overflowing plastic during bridging.
2) top layer is overfilling for no reason, the layer underneath is already smooth as but during the top infill far too much plastic is used.
3) Small perimeters are filled up. Holes of under 3mm in diameter will sag and creep to a solid during printing.
After defining fixed values for the extrusion these problems disappeared completely.

Quote
ChavasRegal
If your seeing scores on the print as the extruder travels across it would seem your print bed is too high, which would catch the top layer and push to wall out as it moves. Have you got a Z hop set?

I understand what you're talking about but why my Z altitude won't change just at the end of the printing except if a mechanical failure occurs, I think. I'm not using the Z-hop feature.

Quote
3dkarma
I think you've diagnosed your own problem - you're over extruding. The reprap wiki has some excellent advice for fine-tuning e-steps per mm to combat this. [reprap.org]

Yes and no ! I checked my settings and correct the plastic wire diameter (beginning of the spool: 2.93mm VS end of the spool: 2.87mm)

Moreover, I have seen the test for fine tuning the Estep but I don't recommend it. The test is based on the presence or not of tiny gaps. The problem is that these gaps are also function of the extrusion width parameters, so it's not reliable.
And also, if I follow the procedure, this test will take 6h and 7meters or plastic

Quote
Downunder35m
I noticed that Slic§r has problems getting the extrusion right in some cases if the extrusion width is not defined.
When I leave all to the default "0" ther is no real problem in 90% of the prints, but for the rest it is a lost print due one of the follwing:
1) not enough filament for infill or top layer, but in return overflowing plastic during bridging.
2) top layer is overfilling for no reason, the layer underneath is already smooth as but during the top infill far too much plastic is used.
3) Small perimeters are filled up. Holes of under 3mm in diameter will sag and creep to a solid during printing.
After defining fixed values for the extrusion these problems disappeared completely.

Really interesting to know because I have the problems 2) and 3) ! Automatic parameter are not always the best apparently...

This is what I'm already using, there are some gaps in a 10% honeycomb but it works well for 100% rectilinear infill. I have a 0.4mm nozzle.



I think I have figured out the problem.... The part itself ! For remember, I'm printing the part with 10% with honeycomb infill

I have tried to:
- Change the Temperature (195-210°C)
- Change the Estep (399-410)
- Change the extrusion width parameters

And nothing changed. Then I have tried to slow down the printing speed at 40% and surprise, the perimeters and the top layers are better. Not perfect but better.


The point is that, if I'm printing a cube, a mechanical part that I have designed or even Yoda, I don't have any problem.... So I think the part is mainly the problem even if my printer could be better setup to handle it. May be I should try with a 0.25mm nozzle.
Cube:


Mechanical part:


Yoda:


Thank you again for your time !

The nautilus gear isn´t that hard to print.
I tried it myself a while ago and even with X & Y scaled down to 50%. I got pretty good results. ( with Cura )
Isn´t it common sense, that slic3r is better for big parts and Cura for small parts?
-Olaf