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?