Getting odd marks on prints

Overall I'm pretty happy with the quality of prints but seeing more of these little points sticking out.

In the first pic attached they are quite clear and on the second picture, the other side, it had less marks.

Any idea's why this is happening?

I believe this has something to do with retraction speeds which also leads me to query the firmware default settings.

The default maximum retract rate is 5000 and maximum retract acceleration also 5000. I have been meaning to ask nophead whether these values (particularly acceleration) require lowering.

Anyway, those figures aside, it could be that the slicer retraction speed is too high and filament is not actually being retracted so when retraction compensation is applied too much plastic is extruded.

This link seems relevant. Here the retraction speed was lowered to 300mm/min which equates to 5mm/s. That is considerably lower than nophead's profile setting of 20mm/s.

Addendum: The X-Y Jerk setting also appears to have an effect on these blobs but I would want to be sure the retraction settings are optimal before modifying that value.

Regards,
Neil Darlow

Edited 5 time(s). Last edit at 01/08/2014 03:04AM by neildarlow.

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

You could try making the infill speed the same as the outline speed as is the case in the Skeinforge profiles I supply. If infill is done at higher speed it needs a higher nozzle pressure. When it retracts, moves to the outline and un-retracts the same distance then the plastic will start at the same pressure it stopped at. This will be too high if the outline is slower than the infill and will therefore extrude too fast to start with, giving a blob.

If you still get blobs it would indicate you need faster un-retracts or a lower temperature to increase the viscosity of the plastic.

If the retract speed or acceleration is too high, such that the extruder motor stalls then you get much bigger errors than those blobs. If it retracts say 1mm then that corresponds to about 56mm of 0.4mm filament. If the retract stalls then the un-retract will make a big loop or blob. If the un-retract stalls you will get a big gap.

Whereas the retract should be as fast as possible, the un-retract speed is critical as too fast will not allow enough time for plastic to start flowing and too slow will allow too much to flow on the start spot. The correct speed will just extrude enough to fill the gap between the nozzle and the layer below and depends very much on plastic viscosity and the outline speed. Unfortunately I don't think any slicers allow the un-retract speed to be different from the retract. They also don't recognise the distance should be different when changing flow rates, hence why I set infill and outline speeds the same.

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[www.hydraraptor.blogspot.com]

I am using the profiles you supply and I have not changed them (PLA0.2, PLA0.3).

I have these little blobs on everything I have printed including using the green PLA supplied with the kit. I'm using PLA from Faberdashery and have used many colours over 10. As I always had good results from each colour (other than the odd few little blobs) I have not changed temperature.

Would you recommend I try lowering the temperature first to see if that helps?

No don't reduce the temperature below 185C. Try increasing the retract speed and or acceleration in the firmware and on the Dimension tab.

It is hard to eliminate them completely unless you start outlines on the inside of the part. You could try altering to loop order on the fill tab to do the inner outline first. That may reduce the dimensional accuracy but give smoother walls.

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[www.hydraraptor.blogspot.com]

Hi,

Quote
nophead
No don't reduce the temperature below 185C. Try increasing the retract speed and or acceleration in the firmware and on the Dimension tab.

Related to increasing the retract speed, some time ago there were a few posts where people were experiencing a clicking (someone described it as clunking) from the X-carriage area. I have just experienced this clicking and noticed it occurs when the extruder changes direction for retraction.

I have been doing some experimentation with retraction settings and you might find that increasing those values introduces this clicking for you. I do not know if it is detrimental to printer operation but it is a little alarming. As a quick test I determined that reducing the retract speed in the slicer causes the clicking to stop.

Regards,
Neil Darlow

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I try to write with consideration for all nationalities. Please let me know if something is unclear.
Printing with Mendel90 from fedora 25 using Cura, FreeCAD, MeshLab, OpenSCAD, Skeinforge and Slic3r tools.

It is just the backlash in the gears. As they wear down you can move the motor to reduce it. It doesn't cause a problem other than being noisy.

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[www.hydraraptor.blogspot.com]

Whosa Whatsis recently updated Marlin to adjust retraction and un-retraction speeds in firmware. I'm not sure if this is preferable to having these set in the slicer but it's possible now at least.