'Thick line' issue with Anycubic Mega 2.0

Hi,

I've now had three Mega 2.0 machines, and they each have an issue with printing. Around 8-10mm into a print, they produce a thicker wide band of material, no matter what file I print. The machines have been setup to the instructions, I've made no changes in Cura etc, and I am using the profile provided by Anycubic themselves. I've even tried other settings in CURA and every time I get the issue.

I contacted Anycubic support when I had the issue with the first machine, and they said it had to be an issue with the Z-Axis thread, so I returned the machine but have now had the same issue with TWO other machines.


I purchased these machines from Amazon. Do they have a dodgy batch in at the moment, as it's the only reason I can come up with as even the tech support person at Anycubic said getting three machines in a row with the issue is like "winning the lottery".

I've attached a couple of pics so you can see what I mean.


Any ideas or possible reasons/fixes would be much appreciated.


cheers

Sam

If the cube had no top and bottom (or just no top) and no infill, perhaps the same number of walls, does it bulge outward or does it bulge inward and outward?

Hi,

On this other print which also had the same issue (this was the owl.gcode which can with the printer), you can see the same bulge line on the inside wall of the print as well.

It essentially bulges the same distance in and out. The bulge line is around 1.5mm tall.

Attachment 16136

The only think I can think it being is that the print essentially 'slows down' at that height, and lays too much filament down?

I'm not a g-whiz g-code guy, but if you can attach the g-code file, I'll take a look at it to see if there's something strange in the slicer output. Consider also to use another slicer (PrusaSlicer is a good one) to see if you get the same results. If you do, it's hardware, if not, it's slicer.

Good call on the alternative slicer, that will be interesting to see.

I've uploaded the gcode from the file I printed last night which also had the issue.

https://paste.pleaseignore.com/index...NhqMWBIZONpCmW

The g-code looks good, which points to a hardware problem. Are you able to observe the nozzle temperature when it reaches the level of the bulge?

Yeh, I'm assuming it must be hardware, but that's three printers all with the same issue I have yet to see anyone else experience?.

I've never really looked for the nozzle temperature, but I'll check to see what the Mega Zero 2.0 can tell me when printing and see if anything fluctuates.

I didn't look at the nozzle temps in the g-code and I didn't examine it to every single entry. The "directives" in the g-code aren't telling the machine to move outward for the bulge. Even a change in the extrusion speed isn't something I examined, but could be a factor. With all these "not examined" factors, a test using PrusaSlicer sounds like a better idea.

Prusaslicer will be first to try this evening. I'll send over the results when complete.

and odd one, because it olooks like a progression. over a number of layers.

Now I get something similiar with my i3. and on that you can see the extruder carriage actually swinging in and out.

So check the sides of the frame in case there uis something the x gantry is moving over that is pushing the gantry in and out.

If all the printers come from the same batch - and it's a machine error. that would make sense.

Hmm. so it's basically an ender 3 with dual z axis. (I'll just rant in silence).

Check the z axis wheels are all tight and also properly round.
But it definitely sounds like a batch manufacturing flaw.
Particularly as it's always at the same height.

Everything seems nice and tight, nothing in the way of the X gantry etc. It MUST be a batch issue.

Interestingly, the listing on Amazon which was in-stock has currently gone out of stock. I wonder if they had a few returned with the same issue?.

try this.

print a block 11mm high say 20mm on a side.

LEAVE it on the bed.
Then print something else 20mm high on top of the existing block. ie starting at 11mm
And see if you get the problem at 11mm on the second print.

If you do - then somehow it's in the software/firmware. if the second print is fine - then it has to be a mechanical error.

Well you can't do it in prusaslicer, annoying. it's a piece of piss in simplify3d.

see if cura will let you do it.

It needs to be two totally seperate print jobs, not two things stacked in the same print job.
We need the software to think it's starting a new print.