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I'm experimenting with my new Ender 3 V2 using PETG filament on the textured side of the included glass bed without any additional adhesives.

I'm been having trouble with adhesion until I found out that enabling raft on my prints helps solve the problem. However, I can't help to wonder whether skirts work any different than rafts.

In my test prints, all settings are identical except for the raft vs. skirt setting (using Cura as my slicer). However, the outer line of a raft adheres perfectly to the glass, while the outer line of a skirt fails to stick completely and moves around when the nozzle goes "around the corner".

Is there any difference between the outer border of a raft and a skirt as produced by Cura?

EDIT: I've managed to upload a video comparison of raft and skirt in the same project.

Nikolai Prokoschenko
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  • What is your bed and hot-end temperatures you use for PETG? First layer adhesion could be related to your Z-height offset as well. Can you share images of your slicer's first layers for both scenarios? This might help to explain adhesion. – Snympi Feb 21 '21 at 04:57
  • I've settled for 240C nozzle / 85C bed temperatures. I can try getting some images and/or videos, but since anything but the raft is just messy spaghetti, this might prove difficult. – Nikolai Prokoschenko Feb 21 '21 at 09:54
  • What is the skirt distance? I set it really close, below 1 mm from the printed object. And the bed on sides is for sure cooler than in the middle... (I got it, it's initial line.) – octopus8 Feb 21 '21 at 11:52

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The raft base (initial layer) is usually printed with very wide lines. Cura's default is double the nozzle diameter, so 0.8 mm with standard 0.4 mm nozzle. This is ridiculously high flow, especially with the default 0.3 mm thickness, which is why the raft base lines are (and must be, unless you have a seriously overpowered hotend) printed so slowly. So, each line has significantly increased (double) surface contact, more pressure against the bed, more forgiveness if the bed clearance is too high (since it will still smash against the bed, just spreading out less than the whole 0.8 mm width), comes out slower (giving it better opportunity to adhere), and does not involve any curves (where the nozzle may "pull" just-extruded material that's not yet adhering).

You may be able to get a lot of the same benefit with skirts (or brims) by increasing the "Skirt/Brim Line Width" setting and slowing down its speed.

R.. GitHub STOP HELPING ICE
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  • Thanks, will try this when my current print is done (it's a long one). However, I've checked Cura's settings and raft speed is 30 mm/s, while skirt speed is set to 15 mm/s, so basically it's already slower than raft. But yes, raft's width is 0.8mm while skirt's width is 0.38mm, so the explanation seems plausible. I assume there is no real benefit in increasing line width on skirt, since the first layer of the print which still not hold? Would changing "Initial layer line width" be sensible? – Nikolai Prokoschenko Feb 21 '21 at 19:01
  • I'm not sure if "initial layer line width" takes precedence over individual feature widths like brim/skirt one. I would think not; if it does, it makes them pointless. And while you could increase "initial layer line width" to get the same benefit for the actual print, you sacrifice the ability to print small details accurately in the first layer. In the worst case, printing of walls thinner than the increased width will be suppressed completely and the second layer will print in thin air. – R.. GitHub STOP HELPING ICE Feb 21 '21 at 21:04