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  1. #1

    Surplus Threads in Print

    A picture is worth 1000 words. I often see these "threads" appearing in a print. They are, I assume, due to the print head continuing to exude plastic is it makes rapid transitions about the piece.I am still playing with it but am open to suggestion. My expectation is that the plastic is too "fluid" at 210 degrees and keeps dripping when it should not. Reducing temperature however has other effects such as bed adhesion issues. I checked with the vendors (SUNLU, Techbears) and I am within their temperature specs. Other thoughts--the GCODE is making transitions that I don't quite understand-a more contiguous pattern would be nice. I have seen GCODE that does a slight retraction during transition's. I don't see that in this code (from Fusion).Ideas welcome!fritz
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  2. #2
    There are a few methods used to reduced stringing like this. The most common and important one is retraction. When printing, the molten filament in the nozzle and hotend is under a fair bit of pressure (e.g., you'll often find extruder systems mention how much force they can apply - often quite a lot). Retraction reverses the filament movement when the print move finishes, releasing the pressure and reducing oozing and stringing.

    A few notes. Too large a retraction setting can drag molten plastic into the heatbreak, resulting in a clog.
    More advanced techniques of dealing with pressure at the nozzle include linear advance (Marlin) or pressure advance (Klipper). Both of these offer a more advanced pressure control than just retraction and can under some circumstances remove the need for retraction altogether.
    Setting retraction on bowden systems can be challenging, as there can be a bit of slop between the extruder and hotend (especially with longer bowden tubes).
    Make sure when setting restraction that everything in the system is well secured. Particularly the ends of the bowden tube, and any other PTFE tubes between extruder and hotend.

  3. #3
    OK--got to the lab this weekend---- my default GCODE (Fusion 360) sets retraction at 0.5mm. This seems a bit low from my reading--Based on all the advice here I put it as high as 7mm and a lot of stringing goes away. But it still is there. Honestly I don't mind spending a bit of time with a blade and cleaning up--but it leaves nasty "spots" wherever you cut away plastic.

    Maybe try higher retractions (I have a Bowden system). Not sure how much I can control speed between dead passes for short distances--probably will have to look at the GCODE here and maybe make up a few false samples that test this-


  4. #4
    Over coffee this morning I had a little time to do some tests as shown. The 3 assemblies have Retraction set at 0.5mm, 7mm and 15mm.The results of threading are pretty clear. In the last, 15mm, example I placed the test post closer together and still no "threads". The distances between posts is 0.1" and 0.75" in the last example.One thing I noticed--the travel between posts is very slow--about 10mm/4seconds. I have "travel" defaulted to 200 in my GCODE generator (Fusion 360). This is fast --I know-- but at any rate I wonder if I am setting this in the wrong place?CheersFRitz
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  5. #5
    15mm retraction is huge, even for a bowden.
    If you can post the gcode file, we can check the feedrates, but just check that fusion is working in mm/sec. it may be working in mm/min, cm/min, or in/min. If it's set to in/min, that would be about 8.5mm/sec

    Also, if it's running in inch/mm then double check that retraction number. It may not be in mm either.

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