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Posted · Small unwanted bubbles

Good morning everyone. I'm banging my head against a problem for which I can't find a solution:

Printer: flsun SR

Slicer: Cura

Material: problem with any ABS, PLA, PETG.

ISSUE: at the end of the initial purge in a semicircle and at the beginning of the print (whether with brim or without), the printer releases a blob of material that often gets dragged along by the nozzle, ruining the first layer, sometimes irreparably.

I've attached here below the last profile I unsuccessfully used to fix the problem and a couple of pics.


Where is the mistake?

Thank you in advance.





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    Posted (edited) · Small unwanted bubbles

    I think your first image shows this one at the end of your StartUp Gcode.

    M82 ; absolute extrusion mode.


    G92 E0

    G1 E-1.5 F1800 ;This is a retraction of 1.5mm

    G0 Z0.5 ; move the Z 

    G1 E0 F300 ; this is a prime of 1.5 while the nozzle is still at the end of the purge arc.


    Put a semi-colon in front of that last line and see if it makes a difference on the end of the purge line.

    An option would be to change the "G1 E0 F300" line to "G92 E0".

    To check the skirt/brim problem you need to post a gcode file.  Changing that last prime line might fix it if Cura is adding a prime at the start of the skirt/brim.


    Edited by GregValiant
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    Posted · Small unwanted bubbles

    Dear GregValiant,

    Thank you very much for your response. I immediately tried your suggestion and obtained a significant improvement. However, I also realized that I can no longer avoid delving into the analysis of the G-code if I want to be aware of the problems and how to solve them.

    So, here I go! I started studying the various commands and interpreting at least the first lines of settings of the various programs. Among other things, I use various CNC machines (lathe and mill) for which knowledge of G-code could help me understand and solve various issues.

    Now back to the main problem. Your proposal has solved the issue to a large extent (let's say 90%). However, the problem arised again at the beginning of the brim, with an abnormal filament extrusion. In fact, the function you made me removing with the "semicolon" is repeated at the beginning of the brim:


    G1 F2400 E0


    So now I have two questions:

    1. Analyzing the command, I simply expect it to extrude zero material and set a speed of 2400 mm/min for subsequent movements: is that correct? If yes, then why does it extrude material?

    2. Is the extrusion considered relative or absolute? I think it's the latter... I ask this because if I've given a retraction command in the preceding lines (for example, -6.5mm), giving E0 will either push the filament forward by 6.5mm or "reset the variable," and the next command will extrude from -6.5mm?

    I hope I've been clear, and thank you for your valuable support.


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    Posted · Small unwanted bubbles

    Look down farther in the gcode.  If the E numbers keep incrementing upwards, you are in absolute mode.

    Since you are fooling with Gcode, Start at the beginning and look for M82 (absolute extrusion) and M83 (relative extrusion).  Cura uses Absolute by default but it can be changed in the "Special Modes" section.



    Cura doesn't "read" the StartUp gcode.  I just sort of pastes it into the file.  Then the print starts with some defaults from Cura like an initial retraction and prime.  If you have done something in the startup that affects where the filament is in relation to the nozzle opening, then the follow up default commands can cause problems.

    Retractions and primes must alternate in the gcode.


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