Mysterious defects...

Hello everbody.

My printer keeps giving Me these weird defects. They appear where the printer stops to move the z-axis up. I have tried to correct it, but I dont understand what is causing it. My settings are:

Extruder: 225 degrees Celsius(the thermisto is a Little off - at 215 it barely prints). Lower temps seem to help, but only slightly and at the expense of quality.
Heatbed:60 degrees
Flow rate 100%(i have tried everything from 70%-100%, and it helps - but only slightly)
I have tried the coasting settings 0,5-5mm(doesnt help)
Higher printing speeds seems to help as well, but again - only slightly.

Anybody have any idea what it could be?

A few things. If using PLA temp is to high. I run at 180 and 70. You should check your "Retract" settings in Slic3r. I run 2mm @ 40mm/sec. And possible overextrusion. Might need to drop your "Extrusion Multiplier" in Slic3r. Mine is down from 1 to .98.

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Maye
Hello everbody.

My printer keeps giving Me these weird defects. They appear where the printer stops to move the z-axis up. I have tried to correct it, but I dont understand what is causing it. My settings are:

In which case, my best guess is that it is retraction settings as most slicers default to using retraction on layer change. For small objects such as that shown, you might get away with disabling retraction on layer change. If not, try progressively reducing retraction. On my particular set up, I haven't found a single "do all" retraction setting and I have to use very low retraction on small objects but have to set it higher on larger objects with big non-print moves otherwise I get "stringing".

Looks like over extrusion.

Print a single walled cube. Measure the wall thickness and then compare it to your extrusion thickness (for perimeters) in your slicer.

Edited 1 time(s). Last edit at 05/01/2016 03:15PM by MrBaz.

I will try that. It seems counter-intuitive to use less retraction when trying to avoid defects, but as my experiments with increasing retraction hasnt exactly helped(anything from 1-6mm even) I would say that its worth trying at least. I will also investigate over-extrusion as well.

Retraction IMHO is a funny and misleading thing
You use it to prevent having plastic where you have to clean it later as inside a model it makes little good use.
Problem is that all this needs to be finely tuned and calibrated as otherwise it can bring more problems than solutions.
In any case it requires a tuned extrusion rate and the right speed - too low and the retraction move takes too much time, especially if you also lift the nozzle.
You want the retrction speeds slightly lower than what the extruder can safely handle.
It is also helpful to know where retraction is helpful and where you can do fine without.
For example a properly tuned machine should not need any retraction for closed areas without holes.
And even for the holes you do without if done right.
Retraction is really helpful every time the nozzle has to start a new section that is not attached to the previous, like arms or legs on a statue.
Here it will make sure there is no unwanted plastic on the nozzle when the first line starts and also that the filament comes out as soon as the print move starts.
Once you can print a nice cube without retraction and no real surface defects it is time to get the retraction right, do it before and the "mess" might only get worse

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Maye
I will try that. It seems counter-intuitive to use less retraction when trying to avoid defects, but as my experiments with increasing retraction hasnt exactly helped(anything from 1-6mm even) I would say that its worth trying at least. I will also investigate over-extrusion as well.

Well you said in your OP that "They (the defects) appear where the printer stops to move the z-axis up." The only thing that happens here is retraction and then un-retraction, so that's why I suggested your retraction settings might be causing the issue. The purpose of retraction is purely to stop filament oozing on non print moves so as a general rule, use the least amount that you will prevent oozing. Good idea to investigate over extrusion as well though. I always use the single wall cube test method on any new roll of filament and then stick a label on that roll with the appropriate extrusion multiplier to use.

Make sure there is no value set in the "retract-restart-extra" settings and the retract speed is sensible say 40.
Though I assumed the small zits elsewhere were due to the layer change. Is this with a Bowden tube?
Make sure the Bowden is secure at both ends.
Are you sure you have the correct size nozzle and have calibrated the extruder.