Bumpy first layer with PETG

  • When I print with PLA, I get a perfect first layer.

    However, when I print with PETG, the first layer looks like this:

    enter image description here

    I've read all the info that suggests reducing the temp, speed, and increasing retraction... I've done all that which has improved things a lot, but I still get this... I can't seem to work out what's causing it.

    How do I get a perfect first layer with PETG?

    The latest settings that I've tried, and produced what you see in the picture are, using Cura 4.3 standard Dynamic Quality 0.16 mm profile with these tweaks:

    • Temp: 220 °C

    • Bed: 65 °C

    • Retraction Distance: 10 mm (not that this would have any bearing on this flat first layer)

    • Print Speed: 40 mm/s

    One thought I had, does PETG need a different clearance between the nozzle and the bed than PLA?

    @0scar I thought the ° symbol was the exception, along with ' and " ?

    Ah no, you're right... ° " ' are only no space if it's used in coordinates, not temp.

  • 0scar

    0scar Correct answer

    2 years ago

    One thought I had, does PETG need a different clearance between the nozzle and the bed than PLA?

    Short answer: "Yes, for some it does".

    The results from your image are typically seen when the initial layer height for PETG is too small. PETG likes an additional gap on top of the usual that is used to print e.g. PLA.

    For me personally I don't experience this general consensus (I've printed kilometers of PETG filament at 0.2 mm initial layer height at a glass bed with 3DLAC spray without any problems), but it is well known that if you print PETG (and if you experience problems) you need to increase the gap between the nozzle and the bed. From "PETG Filament - Overview, Step-by-Step Settings & Problems Resolved" posted on rigid.ink, you see that they (usually) advise an additional 0.02 - 0.05 mm gap:

    Additional PETG gap

    Bottom line, if the normal gap doesn't work for you, increase the gap to see if that works better. Note that in some slicers you can add an offset in the slicer so that you do not have to do the releveling with a thicker paper (or if you are using auto-levelling). E.g. in Ultimaker Cura you can download a plugin (for recent Cura versions from the marketplace) from user fieldOfView called "Z Offset Setting" to get the Z Offset setting in the Build Plate Adhesion section. You can also do a little trick in the G-code by redefining the height so that you can put this in a PETG start G-code or something.

    I have a BL Touch that levels the bed, and I can set a z offset in the printer config. Do you happen to know the name of the param that can tweak in Cura so I don't have to fiddle with config files every time I change from PLA to PETG?

    @BG100 I have updated the answer to include your additional request. Hope it helps!

    I don't think this is the problem in my case, I've tried increasing the gap, but then the filament doesn't stick to the build plate.

    @BG100 what is the initial layer height?

    Initial layder height is 0.16 mm.

    @BG100 That is low for PETG, please use at least 0.20 mm, or a little more (0.24 mm or so).

    Wouldn't an increased initial layer height make more sense? Adjusting the offset will necessarily give wrong volume of material.

    @R..Yes, that is what I do, but an increased gap is reported to work. I've printed kilometers of PETG filament at 0.2 mm initial layer and never ran into such problems but there is a whole community that swears by an increased gap.

    3D printing is an endless source of folks who swear by things that make no sense...

    Sometimes it does, note that the whole leveling procedure causes your nozzle to be not at Z=0 but at paper thickness, so that implies a volume mismatch also, still most folks do this cause putting the nozzle at bed level when Z=0 doesn't work well.

    @0scar Thanks for your help. I actually gave up and switched back to PLA as I needed to get my project done, but I'll refer back to here when I try again when I've got some more time. I'm sure its just a case of tweaking the settings around z offset, layer height, speed, possibly esteps.

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Content dated before 7/24/2021 11:53 AM

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