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I'm currently in the process of fine-tuning my cheap CTC i3 clone. I'm using Cura 3.1 for slicing.

After calibrating the extruder steps, I wanted to optimize the line width and flow compensation parameters. I am using a 0.4 mm nozzle and therefore set the line width parameter to 0.4 mm in Cura. I then printed a cube with 0% infill, 1 wall line and no top layers (basically an open cube with 4 bottom layers). The wall width I measured on the printed result is 0.52 mm. To correct for the difference I set the flow compensation to 80% and repeated the print. The wall width I got from this was 0.45 mm, which is much better than before. There is only one problem: the parallel lines in the four bottom layers do not touch, so the print is not watertight. Up to now I assumed that Cura would calculate the distance between the lines from the line width setting. So with 0.45 mm lines and line width set to 0.4 mm there should even be some overlap.

Why am I seeing this effect? Am I getting something fundamentally wrong here?

Sven Rusch
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3 Answers3

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That is very bizarre. Since GCODE describe each movement of the printing head (so, the printer does not get to decide anything in terms of printing strategy, it just executes), I can only see three possibilities that would explain what's going on.

The print is being scaled up at printer level. This could for example be due to your firmware having your steppers improperly calibrated and moving them too much for a given unit of measure (say you say 1mm, they move 1.5mm instead). This is easy to check: if this is the case, your cube will be scaled up (so - using the example above - if your cube is 10x10x10 it will come out 15x15x15).

You are printing with a raft. Then there is no problem with your set-up, the first layer(s) of a raft are not solid, but intentionally "grated". Check your settings to verify.

Cura is producing the "wrong" gcode. This could be really wrong (as in "you found a bug", in which case you should report it on their github), or just look wrong (as in "you found a weird combination of setting producing that gcode", in which case you should reset the settings to their default and see the problem disappear). Either way, if the gcode is "wrong", you should notice the gaps in the gcode preview mode in Cura.

mac
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It's impossible to get a true measure with calipers because of the bumps from layer lines. The printer/slicer is working on an average of the peaks and troughs but the calipers only measures the peaks. Thus, after measuring and compensating, you told it to under-extrude and it did.

Greenonline
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sam
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Cura does not adjust line width to account for lower flow (aka extrusion multiplier), they are independent settings. Therefore, if you have to reduce extrusion to get the correct wall thickness, then as you said, the lines may not be close enough together to fuse properly and you'll have a weak part. Try reducing the line width. First though, I would take the below troubleshooting steps:

  1. Calibrate e-steps in firmware
  2. Calibrate the actual diameter of the filament you're using
  3. Calibrate flow for the correct wall thickness
  4. Adjust line width in Cura if needed to get proper fusing

Lastly you might want to check for a partial nozzle clog which can cause under-extrusion, though that is usually not consistent

Samwise Ganges
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