I've recently switched to PETG , and I'm using Cura as slicer and Ender 3 as printer.

I'm printing a model which Cura declares to be 35 g, but if I weigh the printed model it weighs 23 g.

I'm printing with just 1 line of skirt, so its weight is negligible on total weight. I've replaced the stock plastic extruder with a double gears metal extruder (3Dman 11 Dual Gear Extruder ).

enter image description here

I've also replaced the stock springs with metals ones.

I'm not having a quality problem, just I want to understand if this difference is caused by a bad configuration that could be improved.

Which are the corrections/checks that I need to do in my setup (both printer and Cura) for fixing this difference?

  • $\begingroup$ In case Cura is being stupid, look at the final E-axis value in the output gcode file to see how much material it's attempting to extrude. Multiplying it by 2.4 ((1.75/2)² × pi) will give the volume of material in mm³ which you can then multiply by the expected density. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 22 at 19:20
  • $\begingroup$ Also: Is it possible there's priming-line, skirt, brim, raft, or support material you're not counting? $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 22 at 19:20
  • $\begingroup$ Good guess, but I'm printing just 1 line of Skirt, just for clearing the nozzle... totally negligible, I guess. Btw I'm adding this information to the question, might be useful. I'm looking for the value you are referring to tomorrow and I'll post you back, thanks $\endgroup$ – Leviand Apr 22 at 19:23

The density of the filament can be specified in the material model of the filament in Cura (Preferences -> Configure Cura... -> Materials and click on the material/filament you are using to slice your model for PETG), look at the value behind Density, the PETG filament I use is using 1.28 g/cm³ (PETG Economy Black -> Specification >).

Cura materials window

This field is user editable, so you can change it to your needs. Cura calculates the weight based on the deposited volume.

  • 1
    $\begingroup$ Thanks for your answer: I've setted the density to 1.27 , but I'm now getting 37gr, which leads to a bigger difference. Is there any other possible problem? $\endgroup$ – Leviand Apr 22 at 11:24
  • $\begingroup$ This setting is used to allow the viewer to determine expected filament use for the print. As you've already discovered, an inaccurate figure will present a disparity between the displayed value and the weight of the print. Changing the numbers will only provide for a value difference, not an operational difference. The other answer (currently) is not likely to be correct, unless you are having model quality problems. $\endgroup$ – fred_dot_u Apr 22 at 15:22
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    $\begingroup$ @fred_dot_u actually I'm not having a quality problem: I'm only trying to understand if my printer is printing correctly or if something is not right setted. This difference has raised a warning in my mind... $\endgroup$ – Leviand Apr 22 at 18:09
  • $\begingroup$ I didn't think you were having a problem with quality, as that would have taken priority, in my opinion. The answer referencing underextrusion appears to be off-base for that reason. If you use trial and error to enter a weight value in the settings, until you get something that matches closely enough, you'll have done no harm. $\endgroup$ – fred_dot_u Apr 22 at 18:14

Likely underextrusion. The Ender 3's extruder is particularly bad at PETG and slips a lot unless you go really slow, like 3 mm³/s (about 40 mm/s at 0.2 mm layers and 0.4 mm line width) or lower.

For a long time I thought this was a limitation of the material, at least without a really powerful hotend, and wondered why anyone liked it. But after replacing the extruder on my Ender 3 with one that grips the filament much better (among other differences) I can extrude at several times that rate with no extrusion issues.

My extruder has a lot of differences from the stock Creality one that might be making a difference. It's (remote) direct drive, has a cut-out hobbed gear that wraps partly around the filament tensioned rigidly rather than with a spring, and has net 10:1 reduction gearing. I suspect the hobbed gear configuration makes the biggest different to increased PETG printing capability but I'm not sure. Here's a picture of what I'm talking about

hobbed filament gears

  • $\begingroup$ Actually I'm printing at 40mm/s , because that's the only way I've found to be able to work with petg and ender 3... and the first layer I'm lowering it to 10mm/s ... Which extruder are you suggesting to upgrade to? $\endgroup$ – Leviand Apr 22 at 12:38
  • $\begingroup$ I'm not making a particular recommendation because there are lots of factors to weight choosing what you want and product recommendations are off topic for this site. I have a flex3drive remote direct drive but it's some work getting it setup well. Mainly for this specific problem I suspect you need either double hobbed gears (both sides of filament) or a hobbed gear cut to wrap halfway around the filament. Mine uses the latter and I suspect it's the better choice. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 22 at 13:31
  • $\begingroup$ You might even be able to get away with just replacing the hobbed gear in the stock extruder, but some reduction might also be needed to increase torque too. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 22 at 13:33
  • $\begingroup$ I've already mounted a double hobbed gears... and actually I'm not having a problem of quality in prints (just some filaments)... how can I measure if my printer is printing the right amount of filament? $\endgroup$ – Leviand Apr 22 at 18:08
  • $\begingroup$ This should be another question/answer pair... letsprint3d.net/… will show you how to check the extrusion values for your printer. $\endgroup$ – fred_dot_u Apr 22 at 18:15

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