PETG settings - just struggling with crumbs/blobs no matter what I try

[shudman]

Being a Newbie, to 3D printing, I started with PLA and PLA+…and feel pretty comfortable with printing with those. PETG, even though I seem to have read every article and tried many settings, I still get blobs, but only on vertical surfaces.
I have been trying different settings with a very simple test model

- and as you can see on the vertical face, there are lumps and bumps along the way…to me, just obvious over extrusion - I can see it during printing, on the hotend itself.
I have tried temperature towers, and 230 or 240 seem to give the best results - I have tried the Snapmaker PETG, Sunlu and eSun filaments (all dried to 50’C in a dryer)
I have no issues with the initial layer going down…that looks beautiful (with a Z offset of +0.1). I also have no issue of it coming off the bed after print.
I am using Luban, and the vertical wall (back and front is seen as an outer wall)
I have tried increasing print speeds from 20, up to 55mm/s
I have tried decreasing flow rates from 100% to 80%
I have tried increasing travel speeds, up to 110mm/s
I have tried different temps from 255’C down to 220’C
I have tried retract at layer change
I have tried Retract distance from 3 to 7mm
I have tried Retract speed from 30 to 80mm/s
I have tried enabling Z-hop from 0.5 to 2mm
Fan at 30%-100%
and combinations of all of the above.
Interesting that Snapmaker’s own spec says to print PETG at 40-100mm/s, but reading on here, that seems fast)
The slower speeds (15-25) definitely give very fine stringing (and I mean very fine), but if I read correctly, then PETG will always seem to do this. Faster print speeds seems to reduce this, but not the blobbing
The base and the side of my test model are 100% perfectly smooth - no issues there, whatsoever

Anyone help me out of my misery here ?

[bobby4718]

A couple of questions, just to get some more information.
Do the blobs only occur at layer changes, or do they occur randomly?
What slicer are you using?
How long do you dry the filament for?
Have you tried disabling z-hop?
Have you tried enabling wipes?

[shudman]

It’s really hard to determine if it is just at layer change. Like I said, the side verticals, both inside and outside are fine/smooth. The layer change happens at the two front points, I believe.
Slicer is Luban - latest version.
Filament drying…5 or 6 hours at 50’C. I bought a dryer purposely, as I thought it had to be that - nope, absolutely no difference.
Yes, initially had Z-hop off
I have no setting for wipes in Luban.

It is not just this test object…I have other box-type objects that exhibited this blobbing (and that is why I just quickly drew up this model, to test different settings).

Appreciate the reply…it is doing my head in now

[ElloryJaye]

Any chance the hole in the tip of your nozzle is abraded out of shape? (This can happen if you use brass nozzles with wood, glow-in-the-dark, and other fancy types of PLA that incorporate other substances.) Note: clutching at straws.

[bobby4718]

Could you upload your gcode? The easiest issue to solve would be if it is at layer changes so I want to make sure this is not the case.
Also, are there strings connecting to these bumps? Could be another indicator of what the issue is.
Finally, I don’t think bad retraction settings are the issue, but sometimes retract distances of less than 3mm work best, try starting at 1mm and incrementing from there. A long shot, but you never know.

[shudman]

@ElloryJaye - no, I don’t think so. It has never hit the bed, and only used “regular” PLA and PLA+.
@bobby4718
testthing1_1649098582554.gcode (155.9 KB) attached the G-code. I have tried to watch meticulously, and up until the 10th layer or so, it is absolutely perfect (the layer is smooth, with zero defects), then as the nozzle goes back on the LHS wall to the corner, then along the longer “back” straight and I might see a tiny tiny piece appear on the nozzle, then it will do the right hand vertical, and on return, you might get a very very fine hair, and then it may crumb. Then it may be fine for a layer or so…then the same behaviour.
Interestingly, and experimenting more, making the wall 3 mm thick (oppose to 2mm), significantly reduces the problem.
I can try reducing retraction again, but as running PETG at 240’C, makes it kinda gooey…and <4mm made it worse, from memory. As you can see…I am trying:

[Arcfay]

Any update on working with the PETG materials? I’m having a similar issue.

[MikeG2]

I have been using PETG for a little while now. I like the durability better than PLA. I usually print as “precise and strong” on my upgraded A350 with dual extruder. I have modified the default materiel settings for PETG and sometimes get some small wispy threads but overall things seem to come out okay. This is my settings export for PETG that I use currently. I do think the fan setting is too high at 50% so I might change that.
PETG-Blue.def.json (4.3 KB)

[MikeG2]

Oh, and I have not received and installed the dual extruder upgrade kit yet so I don’t know if that will make a difference or not with these settings.