too much plastic when nozzle does U turns: gap fill horrible

Discussion in 'Calibration, Help, and Troubleshooting' started by R Design, Mar 17, 2016.

  1. R Design

    R Design Well-Known Member

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    What to do in the following situation (still haven't figured it out a week on)?

    - perimeters OK
    - infill OK

    but bottom layers (on the inside!), top layers and especially gap fill are all problematic

    It looks to me like whenever the nozzle does a U turn there's extra plastic left behind and that rapidly builds up into little piles which are pretty horrible to find on the top layer and make the nozzle bounce on the inside.

    Initially I thought it was because I'd set a wide extrusion width but even on the Simplify auto setting (0.4mm +20%) just the same.

    It's like I can't wait for the bottom layers to be out the way and onto regular infill. Then whenever a patch of gap fill comes up my heart sinks.

    It wasn't nice with PLA but with XT it's horrible.

    What do I need to adjust?
     
  2. Rob Heinzonly

    Rob Heinzonly Well-Known Member

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    There's a guide on the Simplify3D site that will help you in these cases (link)
     
  3. R Design

    R Design Well-Known Member

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    Thanks @Rob Heinzonly.

    It's a good guide, but I don't find my case there.

    The pile-ups occur only when there are rapid U-turns like in Gap fill and at the end points of top and bottom layers?
     
  4. Spoon Unit

    Spoon Unit Well-Known Member

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    It sounds like a case of over-extrusion.
     
    Chase.Wichert likes this.
  5. Rob Heinzonly

    Rob Heinzonly Well-Known Member

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  6. Chase.Wichert

    Chase.Wichert Well-Known Member

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    Have you calibrated your E-Steps/mm, Mine stopped doing that after I calibrated. And corrected the Z Offset
     
  7. R Design

    R Design Well-Known Member

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    The really nasty stuff is inside the parts and seen during printing (no photo).

    But here's

    a) an abandoned print - shows a bit of interior and extrudate sloshing on a corner (not even that abrupt a corner);

    b) the top surface of first attempt with light gray XT;

    The effects will have doubled up on the underlying layers (3 perimeters) and you can imagine on a narrow area of gap fill the effects are really nasty.

    I calibrated and verified 320 esteps/mm for this roll.

    If it was Z offset then I guess it might affect the first layers but then work itself out by higher up the part.

    What else?
     

    Attached Files:

    #7 R Design, Mar 17, 2016
    Last edited: Mar 17, 2016
  8. Chase.Wichert

    Chase.Wichert Well-Known Member

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    320 seems like a lot, why would it matter per roll?
     
  9. goose117

    goose117 Member

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    I had something similar, Using Simplify3D? There was a setting for the PLA profile only that was something along the lines of "Extra Restart Distance". It pushes out this many mm of filament after every retraction. The .fff file had this defaulted to 0.25 for PLA and 0.00 for ABS. Take a look.

    https://forum.simplify3d.com/viewtopic.php?f=8&t=1980

    I had some terrible results when I switched from ABS to PLA, setting this to zero helped tremendously.
     
  10. Chase.Wichert

    Chase.Wichert Well-Known Member

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    From his images it doesn't seem like a retraction thing.
     
  11. PsyVision

    PsyVision Moderator
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    The second one looks like over extrusion
     
  12. Spoon Unit

    Spoon Unit Well-Known Member

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    @R Design , I did two e-steps measurements on two different materials, fed the numbers in, and ended up with over extrusion both times. My solution is to learn to tune the flow rate myself. Knock up a small 2mmx2mm square and watch like a hawk as it draws the first few layers. The base layer alone isn't always the absolute best guide, as it's often printed a little thick anyway, but you can still have a feel for it. On the LCD, go into Tune -> Flow and push the number down until you like what you're seeing. Not you know the flow rate for that material combined with whatever your esteps is, which I no longer ever alter. Give it a whirl.
     
  13. Dr Jeep

    Dr Jeep Well-Known Member

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    Is the height of printed objects coming out as expected what looks like over extrusion could be squashed layers possibly ? If you ask the Z to move 10mm does it actually move 10mm ?
     
  14. R Design

    R Design Well-Known Member

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    Great ideas everyone.

    @Spoon Unit did as you said.

    With flow at 90% it began to print layered inner material acceptably.

    Since I'm not speaking to Marlin at the moment, took the figure and put 0.9 in S3D for the extrusion multiplier instead.

    Test cube is well dimensioned and test part prints much better than before. It seems to be a VERY fine line between under-extrusion (little gaps) and over-extrusion (plastic piling up where you don't want it). Fine to the point where you're going to get a bit of one or a bit of the other and it's a compromise. Is that right?

    With hindsight it's apparent the the roll of E3D PLA that was spot on 304 e-steps/mm needed an extrusion multiplier (flow) < 1 as well. Implying that the supplied BB pro profile is not quite ready to go for PLA. (However not all prints / slicings will reveal that...)

    Where does this multiplier come from? Since matter is not being created or destroyed, is it to do with thermal expansion? That PLA and Colorfabb XT expand a good bit in the meltzone and so there's more coming out than you put in and that must be compensated for?

    We have the title "What they didn't teach you in the BB Build Manual" - who's going to write it?

    ;-)

    ps what kind of compensation factors is everyone else using?
     
  15. Spoon Unit

    Spoon Unit Well-Known Member

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    I'm really no expert at this yet, but I do watch what's happening a lot as that's the most direct feedback method. Underextrusion gives you holes in your print between the infill and outline lines. Overextrusion gives you too much material on the bed and, from the right angle you'll see straight away that there are little tufts of material above the build layer. Tweaking it on the fly via the front LCD panel, or via OctoPrint (Flow Rate, not Feed Rate) let's you tweak it until you're dead on. I then write that number on the sticker on the spool. In theory, flow rate is just a GCODE that you could include in your profile (if you really a profile per material) or tweak at the last minute (I always still seem to quickly scan through and tweak at the last minute).

    I've currently got red e3d everyday PLA printing. I think the eteps are 292.3 (from the last time I ran an actual measurement) and at present I think I have the flow rate at 88.

    Part of the challenge is that the first layer is always printed thicker to a greater or lesser extent in order to assist with bed adhesion. Two thick and you'll loose any detail on the bottom (embossed lettering in the case of the Benchy). Too thin and your Benchy will be sailing a little too soon.
     
  16. mike01hu

    mike01hu Well-Known Member

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    So much depends on the dimensional stability of the filament, which can vary substantially over the length of a reel for lower grade products; even good stuff can vary but hopefully not too much. My experience (K8200) to date has been with 3mm filament and variations on that are more noticeable during printing than with 1.75mm product i.e. a diameter change on 3mm filament means more volume for a given length than the same diameter change on 1.75mm stuff. It is good practice to print test pieces with each new reel and I have never had to retune the steps for PLA to correct for extrusion variation other than by tweaking the extrusion multiplier up or down a % or two.

    For the base layer it is important to have no gaps between filament lines for good adhesion and to try and ensure those edges are fused but without too much spread; I usually print a single layer test piece to check this. Any bottom layer features are easily cleaned if slight over-width traces occur.
     

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