• I am curious, what is the purpose of printing a single-height outline around the objects to be printed?
  • Also, how would it affect the outline if the object to be printed extends to (very near) the very edge of the print area?

finished print on print bed, with outlines annotated

Update, I received a hint that an existing question has the answer; that link was not really to my satisfaction -- but it did link to another one that did: What are main differences between rafts, skirts and brims?

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    $\begingroup$ Hi welcome to 3D Printing.SE! Note that this question is similar to "Random lines are being printed?", one of the answers discusses the purpose of the skirt. $\endgroup$ – 0scar Apr 20 '20 at 12:14
  • $\begingroup$ It's a skirt, skirts are a method of adhesion. I print without usually, but for very thin objects I use a brim $\endgroup$ – Trish Apr 20 '20 at 12:19
  • $\begingroup$ Does this answer your question? Random lines are being printed? $\endgroup$ – Trish Apr 20 '20 at 12:19
  • $\begingroup$ Thanks for the update, but the question you linked does not describe all the benefits of the skirt, it is a good question from the beginning of the beta days! $\endgroup$ – 0scar Apr 20 '20 at 12:46

I am curious, what is the purpose of printing a single-height outline around the objects to be printed?

The (equidistant) lines at distance from the print object is called the "skirt", the skirt is an option found under the "Build Plate Adhesion" options in your slicer. The primary function of the skirt is to get the flow going, but there are more benefits you can get from the skirt:

  • You can find out whether the bed is correctly levelled, or if the bed has concave or convex areas (the skirt should be a line, I prefer at least 2 lines, of consistent thickness, if not, this may hint to incorrect levelling;
  • You can find out if there is enough or a sufficient amount of adhesive (e.g. glue stick, hair spray, specific print adhesion sprays like 3DLAC or DimaFix, etc), if not the bed might be greasy or lacking the adhesion product;
  • You can configure the skirt height to use the skirt as a shield for draft or ooze and distance to product);

Also, how would it affect the outline if the object to be printed extends to (very near) the very edge of the print area?

Do note that a skirt limits the useable build area by the distance and width of the skirt.

Basically this has been answered (see this answer and this answer) in a different question ("Random lines are being printed?"), but it might be beneficial to answer this question rather than closing this for a dupe. This question is focussed on the skirt, the equidistant lines around the print object, while the other question focuses on the priming line.


My understand is that's is basically a purging extrusion, so that you get flow through the extruder before you start printing the object, as filament that's been inside the hotend during warm-up might have been "overcooked" by spending too much time in the hotend at temperature. It also helps stabilise the PID loop controlling the extruder temperature by allowing the PID loop to stabilise the temperature of the hotend as it's got filament flowing through it compared to it being idle.

It also shows the user where it intends to start printing, which is a useful check if something went wrong with Gcode generation.

  • $\begingroup$ Aha, so based on your first paragraph, it might as well be shaped as a squiggle in some corner of the bed, yes? The way it is usually presented means the amount of purging depends on the area of the base of the model. $\endgroup$ – KlaymenDK Apr 20 '20 at 11:43
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    $\begingroup$ Exactly, the idea is that the printer purging line handles most of the purging of the "bad" plastic, and the outline is just handles the "temperature stabilisation", which scales with the model for probably no other reason than that the slicer doesn't have to figure out where it can put the purging lines (since there's never going to be a print outside the models on the bed). $\endgroup$ – Stuggi Apr 20 '20 at 11:52
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    $\begingroup$ It's also a good check of whether the print bed is level/at the correct height. I frequently make small Z babystepping adjustments while the skirt is being printed so it's in the exact right position when printing starts. $\endgroup$ – Tom van der Zanden Apr 20 '20 at 12:25
  • $\begingroup$ @KlaymenDK: Indeed, I find a prime line along the very edge of the bed far better than skirts. Every time I've tried enabling skirt, the inconsistent extrusion at the very beginning (from the nozzle not being primed yet) causes some material not to adhere right and get dragged around, and in some cases this actually messes up the beginning of the actual print! Doing priming as nothing but a straight line ensures that nothing can get pulled around before it starts adhering. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 20 '20 at 18:14

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