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I've got several examples like the image below where the perimeter either doesn't bond to, or doesn't reach the infill. I tried adjusting the infill overlap parameter in Slic3r from its default of 25 % to 30 %, but it doesn't seem to have made a difference. This is on a new Tevo Tornado that's all stock + a Petsfang Bullseye cooler.

Visible separation on perimeter of the inner box

Neither speed variations, nor temp variation seems to impact this issue. I'm beginning to suspect that it's related to some sort of play in the Y-axis, as if you look at the defect in the picture, it's the most pronounced running north/south in the picture, which would be layers along the X-axis (meaning their relative position would be impacted by Y-axis movement instability). I'm replacing the leveling springs with PETG standoffs tonight (I have a BLTouch) and will try again then.

I tried 25, 30, and 50 % infill overlap as per a comment request, and that (50 %) seems to have improved another issue where the infill on a first layer would often not reach the perimeter shells.

I tried the following print speeds with all of the following temperatures (nozzle/bed): 190/60 °C, 193/65 °C, 193/70 °C, with 3 perimeters.

Default parameters

That's default behavior. I've also gone to

  • Perimeters - 80 mm/s
  • Small perimeters - 20 mm/s
  • Infill - 90 mm/s
  • Solid infil - 25 mm/s
  • Top solid infil - 20 mm/s
  • Bridges - 70 mm/s
  • Gap fill - 25 mm/s

With no visible change in this outer perimeter behavior (the faster set of numbers is what I print with in general).

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  • $\begingroup$ 30% should be plenty, but did you try a higher percentage overlap? $\endgroup$
    – Davo
    Commented Apr 12, 2019 at 19:08
  • $\begingroup$ @Davo yeah - the default is 25, i tried 30 with no visible diff. $\endgroup$
    – kolosy
    Commented Apr 12, 2019 at 19:37
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    $\begingroup$ So you did not try anything higher than 30%? Please try 50% - not that I think this is the fix, but I'd like to see what (if any) visible effect it has. You can cancel after a few layers. $\endgroup$
    – Davo
    Commented Apr 12, 2019 at 19:42
  • $\begingroup$ please add if you have "print thin walls" $\endgroup$
    – Trish
    Commented Mar 18, 2020 at 17:00
  • $\begingroup$ Which material are you printing, considering the temperatures for the hotend I would guess PLA (bed temperature is rther high though). $\endgroup$
    – 0scar ♦
    Commented Jun 30, 2021 at 15:45

2 Answers 2

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This has nothing to do with the infill overlap, the image you've added looks as if the issue is related to non-bonding perimeters (it looks as if it is in between the 2nd and the 3rd perimeter), hence infill overlap doesn't apply here. If that is the case look into this question.

I've had this same issue, the problem is that if the perimeters do not touch, this is most probably caused by insufficient filament flow which can be a result of a too high of a print speed (or too low print temperature) of the inner perimeters. This is frequently seen when printing PETG. PETG has a limited print speed, the PETG I use (premium brand) has a maximum speed value of 50 mm/s, your values are for some values over that value. That would be fine for PLA, but high for PETG, the question is not clear on the material used for this print (the hotend temperatures hint to PLA, the bed temperatures are rather high though).

If it is not related to the material being printed, these gaps are also explained if the positioning of the nozzle is not correct, e.g. caused by loose belts. This is supported by the comment on the first layer:

where the infill on a first layer would often not reach the perimeter shells

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I had absolutely the same issue. And after some research I finally found that this is because of wrong pressure advance setting (In case of Marlin - linear advance) in the firmware. Without pressure advance (linear advance) will be more plastic at the end of the travel rather than at the start. As result the fast full infill will have uneven distribution of the plastic with more plastic close to the perimeters that usually produce rounded corners. The pressure advance makes it better and redistribute plastic flow more even with the speed however if you make this setting too big for your 3d printer and filament then this will result in what you can see on the picture with less plastic at the end of the travel. Basically too big pressure advance parameter will result in less plastic near the perimeters and especially near corners where change in speed happening.

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    $\begingroup$ ...result in less plastic near the perimeters and especially near corners where change in speed happening The image of the OP shows the exact opposite of what you describe, the image shows filled at corners and free at the wall perimeters. $\endgroup$
    – 0scar ♦
    Commented Mar 18, 2020 at 22:10
  • $\begingroup$ In the middle of the image where the square part is, clearly visible that perimeters are clearly separated from infill. This is it, the fast infill has less plastic extruded and not touching perimeters. This is not happening everywhere actually because of variations in speed. Also tuning different parameters result in all possible effects but the worst part when weird things happen like infill is good but all perimeters are fully separated even from each other. $\endgroup$
    – Serge Rabyking
    Commented Mar 19, 2020 at 18:37
  • $\begingroup$ Of course, decreasing the speed will also decrease pressure advance effect which is actually introduced for high speed. Actually low speed is a cure for most problems but everybody wants high speed. I also originally solved my problems with lowering speed but good guess and proper tuning of pressure advance parameter made me lucky to print now with good quality and twice less time. $\endgroup$
    – Serge Rabyking
    Commented Mar 19, 2020 at 19:17

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