Gaps in top and bottom layers, no under-extrusion

[lukasz_b_g 0]

Hi,

I know this question has been asked before, but no other thread that I looked at answered my question.

Recently i started getting gaps in my top and bottom layers, I can't say exactly what I changed when this started happening. I thought it was under-extrusion, even though the walls were fine, so I re calibrated my extruder to ever so slightly over-extrude, and no effect. I decided to count the lines on the bottom of the cubes.

I calculated that: It's 20x20, so the hypotenuse is ~28.29 (the top/bottom pattern is diagonal)

The cube (yellow) cube has 2 perimeters, so 28.29-2*2*0.4=26.68

26.68/0.4, because the lines should be 0.4mm amounts to almost 67 lines on the top and bottom.

I took a strong magnifying glass, and tried to count the lines with precision tweezers. I counted 32, so there are probably 33, which would be exactly half of what the should be.

The blue cube is sliced in cura 2.5 beta, and the yellow in 2.5.

The setting are the same in both slicers.

Both cubes are in pet g.

[DaHai8 70]

Here are some possibilities:

1) Partial clog: Try a Cold/Atomic pull method to clean the hot-end

2) Incorrect Nozzle/Filament size set. Make sure nozzle size is correct for you printer and Line Width is the same, or slightly larger than nozzle size

3) Printing too fast: try a slower overall Print Speed

4) Slipping/Gummed up Extruder gear: check/clean the extruder gear and idler wheel of any gunk built up on it. Also try tightening the pressure knob. Of course, it could be too tight and the filament is not sliding past on the idler wheel.

5) Printing PETG too hot or its contaminated with moisture: Do you hear popping when you're printing? Do you see little explosions of vapor when it extrudes filament? Is the filament rough (not smooth) when you manually extruded a few centimeters? These are all signs of either printing too hot or having filament that's absorbed too much moisture. There are multiple Googleable sites on how to dry out PETG. Or try printing 5-10c cooler

6) Printing too cold (yes, could be that too): do your parts delaminate easily? If you are printing too cold, then the extruder has difficulty pushing the filament through and can under extrude (even if the sides look OK). And if the filament is too cold out of the nozzle, it will not laminate properly to the under layer.

7) Your hot-ends thermistor is going bad and not reporting the temperature correctly: This can cause an overheat or underheat and show the same results. Had this happen to be and had to replace the thermistor and recalibrate.

That's all I can think of at the moment!