COMPLETE Print head priming GCODE

Discussion in 'Guides, Mods, and Upgrades' started by Spoon Unit, Nov 13, 2016.

  1. Spoon Unit

    Spoon Unit Well-Known Member

    Sep 6, 2015
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    A while back I was watching one of Tom's videos and heard him say something about modifying his prints to create a priming line at the edge of the print bed instead of using a large skirt. It occurred to me that this is really just a question of teasing some GCODE from an existing print, doing a few calculations for extrusion and then setting my scripts up as part of my slicing step.

    Given that this essentially means modifying your script for (almost) every print, it may not be for you if you just want to select a profile and go. No problem. For me though, it seemed like a neat way to get another level of control into the printing process.

    I started by creating a 100mm long straight thin piece then, setting that up to print, then looking at the GCODE. This was my starting GCODE:

    G1 X115 Y200 Z0.3
    G1 X215 Y200 E5.9868 F600

    I added this immediately after the undocking step. In S3D you can see in the preview how this now shows where that prime line will be:


    This didn't work quite as well as I wanted, and I realised this was because the longer the move step is between two points, the more likely that, particularly at the start of a print, you'll have a moment to wait before extrusion fully restarts. So the next thing to consider is how you've set up your layer start points. Much of the time I'm using a specific point in order to collect the seams, but regardless, you can use the S3D viewer to see where the start will be:


    Now you know where your print starts, you can control that initial GCODE line to end close to where the print will begin. i.e.:

    G1 X265 Y100 Z0.3
    G1 X165 Y100 E5.9868 F600

    Which then gives us this:


    Making a specific length of extrusion rather than guessing the number of skirt lines for small objects, or completely overdoing it for large objects seems to make a lot of sense to me, and gives you back the entire bed (minus your prime line).

    Oh also, you don't really need to fiddle with my numbers too much, or alter it for the layer height of your model. The beginning of your actual print will lower (or raise) the head to your selected layer height. Actually, come to think of it, the nozzle size will be a factor here. I get this from using a 0.4 nozzle. Glad I've thought of that as it'll need adjusting if I go up or down nozzle size.

    Anyway, there's a process there you can follow if you really want to. Hope it helps someone.
  2. Stefan

    Stefan Well-Known Member

    Feb 17, 2016
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    hmmm ok... but I would like the Slic3r feature where you can define "print a skirt of min XY mm" is S3D.

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