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Trouble with Cura and stringing

Posted by jbernardis 
Trouble with Cura and stringing
November 14, 2014 12:38PM
I try to use cura as much as possible because I get better results as far as dimensional accuracy goes. It also handles thin walls well. It does have its warts though. I think bridging could be improved a bit, and for the life of me I can't solve the stringing issue I am seeing. On virtually every print, I have to use an xacto knife to trim off all of the hairs. I have increased the retraction distance to 4.5mm as suggested by the tool tip within Cura, but it is still a mess.

Since I have absolutely no stringing with slic3r, I decided to take a look at the G Code that gets generated when the head moves from one object to another on the same layer and compare that to Slic3r's G Code. The object I used was simply 2 10x10x10 cubes 10mm apart. I went to the same layer for each slicer and located the point where it moves from one cube to the other, and here is what I see:

For Cura:
G1 F900 X113.963 Y102.835 E31.50598
G1 F1800 E27.00598                                       <== Retraction of 4.5mm
G0 F9120 X94.160 Y104.160
G1 F1800 E31.50598                                       <== Reversal of retraction
G1 F900 X85.840 Y104.160 E31.63550

For Slic3r:
G1 X106.244 Y96.204 E3.78236
G1 F1800.000 E1.78236                                 <== Retraction of 2mm
G92 E0
G1 X91.124 Y104.173 F7800.000
G1 E2.00000 F1800.000                                 <== Reversal of retraction after axis reset
G1 X85.827 Y104.173 E2.08056 F776.572

Nothing appears out of the ordinary. Slic3r does an axis reset, but that's fine, and cura uses a G0 instead of a G1, but Marlin treats these commands the same.

The only other theory I have is that the Cura travel speed of 9120 mm/m (152 mm/s) might be too high. Perhaps the travel is not complete when the retraction reversal starts??? Slicer is using 7800 mm/m or 130 mm/s. It doesn't seem like much, but it's easy enough to try. When my current job finishes, I'm going to do that.

Can anyone think of other things I can change??
Re: Trouble with Cura and stringing
September 18, 2015 04:37PM
I'll throw out a few.

The retraction (and all other commands) completes before the next gcode is executed. I don't think the travel speed is involved, but you could make them the same and test it.

Are you sure the printing temps are the same?
Are the retracts always happening?

Are you using a Bowden extruder? If so that retract distance may be on the lower end, try increasing the retract distance.

Your retraction speed is only 30mm/sec. Can it retract faster? Generally retraction can be faster than un-retract due to back-pressure on the filament.
One reason to retract faster is that the nozzle is stationary all the time it is retracting, and the longer it takes, the more of a blob is formed at the end of the segment (depending on many factors) - possibly this could contribute to stringing.

My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
Can you answer questions about Calibration, Printing issues, Mechanics? Write it up and improve the Wiki!
Re: Trouble with Cura and stringing
September 22, 2015 03:05AM
The thread started in November 2014, Paul grinning smiley
Re: Trouble with Cura and stringing
September 22, 2015 11:51AM
Not sure how I missed that. Can't delete it now...
Re: Trouble with Cura and stringing
September 22, 2015 10:18PM
I'm still here smiling smiley

I'm still in the same situation with cura, but it's a minor issue to me. As slic3r has advanced. in my mind it's gotten better and better. I rarely use Cura anymore.
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