PETG on Ender 3

I've been trying to print some eSun PETG on my Ender 3 with some questionable results. I am experiencing severe stringing. Attached is a photo of my first layer. My settings are:

• 250 °C hotend
• 80 °C bed
• 0.15 mm first layer
• 0.2 mm layer height
• No Z-hop/retraction
• 40 mm/s print speed
• 50 % fan speed

Any suggestions?

• Increase the first layer, PETG usually requires a larger height for the first layer. – 0scar Jul 1 '19 at 5:51
• Ok I will try that later – Sean McC. Jul 1 '19 at 5:56
• Furthermore, rpm has to be low to get PETG layers to bond properly. This depends on the used fan, 50 % can be a lot or not much depending on the fan duct and fan. An additional Z-offset (like leveling the bed with a thicker piece or multiple pieces of paper) is reported to work for many people (note that some slicers can add a Z-offset, e.g. through a plugin). – 0scar Jul 1 '19 at 10:26
• From my experience, stringing like that is due to a restricted filament path. Have you taken a look at the feeder setup: extruder gear, boden tube, and nozzle? Look for clogs. – ifconfig Jul 1 '19 at 12:40
• The bed may also be too high. The texture for the skin fill makes it looks like that's a possibility, and it would restrict flow, making the stringing more likely. – R.. GitHub STOP HELPING ICE Jul 1 '19 at 17:25

It looks to me like you're using Cura with the default Ender 3 custom start gcode. The priming line there tries to cram about twice the amount of filament through the nozzle as what it should, so unless your material and temperature can handle really fast flow, you'll build up pressure in the bowden, the retraction before the move to start printing will fail to actually back the filament out enough to stop flow, and you'll get a string. This will continue until sufficient oozing has happened to dump all the excess filament.

Going back and forth over the same line is also problematic, as it will pick up any blobs that got dropped off the first time over, melt them on the nozzle, and drag them into the print area. PETG really hates that. Whereas with PLA it just tends to leave the junk stuck to the model somewhere, with PETG it'll get dragged around and break things off the build plate or the model.

I replaced the priming part of the start gcode with:

G1 X0.1 Y20 Z0.3 F5000.0 ; Move to start position
G1 X0.1 Y200.0 Z0.3 F750.0 E18 ; Draw the first line


Note that there is no second line.

I also reduced the final retraction in the end gcode from 3mm to 1mm so that the filament is left in a position where it doesn't require a lot of advancement to start priming, comparable to what you get after loading filament manually. Otherwise, you need extra priming at the start to make up for the difference, and then after loading new filament you'll over-extrude during priming.

Oh, you also need retraction, regardless of material. I missed that you had it off. Anyone telling you to turn off retraction for your general settings is wrong as that will always cause stringing; it's just a matter of how much1.

1 - see discussion in comments.

• a little confrontional on the retraction side: under some circumstances (flex filaments) it can be better to turn it off. – Trish Jul 2 '19 at 12:30
• @Trish: I disagree strongly. I've seen that claim plenty of times, and turning it off can be a mitigation vs extruder mechanisms where the flex filament gets stuck, but turning it off with flex filaments will result in extremely bad print quality (and hard to fix in postproc due to properties of the material) unless your print has single components in all layers. The right solution is adapting the extruder to accommodate the material. – R.. GitHub STOP HELPING ICE Jul 2 '19 at 14:42
• Getting started with flex materials and with 3d printing in general, bad advice about turning retraction off was one of the most frustrating things I hit and wasted lots of time on. So if I'm a little bit confrontational over it, there's at least a reason. – R.. GitHub STOP HELPING ICE Jul 2 '19 at 14:44
• It's highly circumstancial, and in most cases, retraction is good or better, but for some small cases. As a general advice: yes, turn it on. However, one should be aware that there are some small cases where turning it off can help. I suggest turnign the Anything into an Anything* with a notion about some fringe cases - in those cases Stringing will happen, but you take the stringing to fight other, bigger issues. – Trish Jul 2 '19 at 15:01
• @Trish: Yes, I think that's right that it can be an intentional tradeoff to mitigate other issues. But general advice to turn off retraction that's not tailored to a specific situation and that's not framing it as a tradeoff, but rather "what you need to do to print this material" or similar, is what I'd call wrong advice. The only way "retraction off" could be generally right for a material is if the material had essentially zero compressability and zero flow without an applied force, and that's exactly the opposite of the properties it typically gets recommended for. – R.. GitHub STOP HELPING ICE Jul 2 '19 at 15:12