I printed a model of the bust of The Hulk. Green PLA, nothing special.
It looks like ablob of PLA intermittently drags across the model for a short distance, leaving what looks like a scratch, then the blob disconnects from nozzle and sticks to model.
But the part I do not understand is that the scratches/blobs are not consistent.
If you look at the model as a cube of six sides, Top, Bottom, Front, Back, Left, Right.
Bottom, Top, Left, Right, Front are blob free, Back is littered with these blobs.
See these.
No, I did not.
I’ve made models of different objects that would have been the same general volume but have never seen this before.
The texture of the model is sort of unusual which I attribute to how they went from an animated cartoon character to a 3d solid model
Seams are white.
From above front.
This was an overnighter to try and give the 3 AMS rig some run time and I probably would not have noticed it because of how it primarily impacted the back of the model.
Firmware does not affect the seam supports, that’s solely in the slicer.
The likely issue is that pressure advance is not properly calibrated. To really diagnose this, it would help to understand the underlying infill and wall layers. If a nozzle is, for example, traveling to the edge of the infill and the walls are set to 1 or 2, the nozzle can sometimes overshoot the runway and leave a blob if there’s too much filament in the nozzle.
There’s another theory, but it’s usually seen only on Clipper machines. Several articles discuss blobs/zits caused by the processor being overwhelmed. Given the size of your model, you might be pushing the limits of G-Code processing. Although Bambu is not running Clipper, one possible Bambu-specific cause could be SD card corruption. If there are bad sectors that the MPU has to re-read, it could cause stalls in nozzle feed and movement, which would mimic what we’re seeing here. A simple test is to take a different SD card (not the one you’re currently using), format it, re-send the print, and then compare the results side by side. It’s only theory so keep it in mind.
The only thing that throws a wrench in the dry filament theory is that it is on just one side of the print. If you unwind the print, it is like one long string of filament loops with a portion of each loop being moist rather than the entire spool. It seems more like in every linear foot of filament, between inch 3 and inch 5, the filament is moist (for example)
This model was a random choice based on consuming the tail end of some olive green PLA
That suggests that your use of the auxillary fan may be a factor. Try rotating your model and see whether the zits move on the model surface but otherwise remain facing the same part of the printer.
Or, it could be that overhangs in that part of your model are a lot different than the other sides of the model, in which case your part cooling fan may be blowing on it differently. You can check for that by looking at the line types of those regions in the print preview after slicing. Overhangs will have a different color (usually dark blue in my experience). You can also use the fan view in the after-slice print view to check for differences in part cooling fan speed.
Which slicer view is this? It looks almost topographical. I’ve never seen one with that kind of appearance before.
These blobs:
Sure do look like bubbles. I wouldn’t be surprised if they’re somewhat hollow inside.
I’d blame that on (a lot of) moisture in the filament.
Randomness also supports that conclusion. These are not bad PA and random Z seams or there’d be a lot more of them.
These trails are because steam in the hot end blew a bubble of plastic out, so until the extruder catches up with the void that the bubble created just inside the tip of the nozzle, there’s little or no plastic flowing.
Having removed the blobs with an exacto knife, and filed down the remains, I can confirm they are solid.
I’d be more in the moisture camp except it all happened on one side of the print. If the filament was saturated evenly, the blobs would be throughout the print.
I think a portion of the filament is saturated, the rest isn’t but I’m open to suggestions as to how I can test that theory.
You could certainly soak or dry a spool and get all the filament uniformly saturated or dried. But in an uncontrolled environment, moisture levels are going to vary. One side of the spool sees more sunlight, or a stronger draft, that side is going to be drier than the other, for example.
Drying isn’t the cure for every issue. But it’s often the cause of many. If you’re not drying, even though it’s PLA, drying is the first thing to try.
What I might suggest is to do a simple spiral vase mode on a large cylinder in order to replicate the motion of the object. In fact, here is a model that may serve as a possible test candidate. It is two cylinders, 150mm in diameter that have been Boolean merged. The model is only 0.5mm thick so it shouldn’t be able to render more than one wall and as such should produce a motion similar to what your are currently doing.
Click to zoom to visually see where the seams will land.
Although plate #4 has scarf joints enabled, it should not work any differently than plate #1 because for scarf joints to work, you need more than one layer but in this case it’s simply a test.
Scale the height or the entire model if you don’t want to use all this filament but you may run into resolution issues and the slicer won’t render if it’s scaled too thin.
