Printer under and over extruding??

Hi folks,
been trying to print some brackets for v-slot and the beast is exhibiting some strange behaviour.
The top surface appears be being over and under extruding in strips. Well either that or the
nozzle is oscillating between two different heights.

I've attached a photo but taking a picture of a black object is a bit of a bugger.

Any suggestions?

Andrew

What are you printing with?

Are you sure your nozzle isn't getting partially blocked? Heat creep for example.

Did you try slowing the print down (e.g. 20mm/s) and seeing how that goes?

The differences I see on the pic seems to be slicer related because they follow a pattern. Maybe you've set different extrusion_width for top infill and perimeters?

It shouldn't be a dirty nozzle. Only just a week or so ago pulled it to pieces and cleaned it.

The weird thing is, as o-lampe, noticed is the flat strips are symmetrical over the top.
If the nozzle can go from one side of the print to other, i get a smooth strip. But if the
nozzle is interrupted by, say a bolt hole, i get what appears to be over extrusion.

My settings.
Slic3r with default widths.
Extrusion multiplier set to 3 or so points under ideal
0.3mm layer
Printer 30mm/s 245^c
PETG, fresh roll

Since the Z height doesn't change and the hot end is actually moving to the correct positions it can only be an extrusion issue.
I don't expect this is due to Gcode (check if you want) so its about flow rate through the hot end.
With modern tensioned idlers on the extruder you can overcome grinding situations since the filament is pressed against the hobbed bolt regardless of the filament size. So this issue can be due to changes in the filament diameter or changes in the flow at the hot end.
Check the temperature at the hot end possibly increase the temperature. This would be my best guess. Check the heater is securely attached to the heat block. Check the thermistor is securely attached (less likely to be an issue).
If for whatever reason the nozzle temperature is cycling you may get periods where it extrudes easily and others where its to thick.
Remember that the temperature reported by the software is the temperature reported by the thermistor which is not the temperature of the nozzle. Hence the need to check the installation of the parts.

Actually MCCarmen, I have to disagree about the z axis not moving.
I use an inductive bed sensor, so the z axis/ nozzle height is constantly changing whilst printing.
So I can't rule this cause out.
The extruder, Bulldog Lite, what a rip off, likewise has just be readjusted when I redid the
hotend. It should be dialed it just right for PETG.
My filament, Torwell3d, is actually remarkably consistent for filament diameter. Definitely
worth spending more on filament.
But running a recalibration on the hotend is probably overdue. Just have to finish
wiring up a thermocouple.

You could setup a single wall print and experiment with temps and speed. Increase external perimeter width to 0.6 in slic3r. That'll be a stress test for the extruder.
If your extruder works like mine, you'll see a speed where the extruder starts skipping steps and the wall will be thinner then.

Okay,
an updated photo that worked. I've reprinted the file twice and the same
smooth/rough parts occur.
Changed slic3r from 0.5mm for all thicknesses to auto.

Trying the calibration cube with over thick walls should be an interesting test.

I suggest printing a single wall cylinder, for more constant print speed. Vase or not won't make a difference.

I've seen similar issues as well. It seems to be apparent after a retraction.

Are you using a bowden tube to feed the hotend? Do you have extra length on restart set to a non-zero amount in your slicer?

Hi folks,
tried everything but nothing helped.
Appreciate the help.


Andrew