At such low flow rates there should only barely visible changes on the print.
I print with flow rates as high as 40 and the flow rate changes for complex models are correspondingly large.
I see this artefacts happen every time the layer time changes too much AND every time the flow rate changes too much.
The first I try to explain with the pressure in the melting chamber and the hotend overshooting a bit.
CAN explain but shouldn’t have to because my other printers don’t suffer from this any way - use the Bambu ones.
The overshooting is only an issue for me with my high flow rates but won’t happen on the Bambu hotends with their low capacity flow rates.
On top of that comes the problem that physics won’t work this way!
The issue would have to be consistent in order to being a general one.
We are not talking about the minute amounts of plastic getting out too much due to the hotened design and flow changes.
We are talking about often OVER a millimetre sticking out from the model - this requires a change in the extrusion path to work!
There is quite a few topics about this in the forum where users also show pictures of the issue and how the printed model is so far out for certain sections that you can see the layer lines building up that angle.
A good calibration for the filament helps for the minor issues caused by flow rate changes and lowering the acceleration values a bit fixes the overshooting problem after sharp corners or small diameter curved paths.
Seems clear that for these cases we deal with pressure advance calculations not in line with the movement calculations.
For those really severe cases of things starting to literally poke out of the model I have to assume that something in the slicer is going wrong or that the printer firmware gets a hickup.
Changing to a lower layer height also changes ALL slicer calculations for the paths - so it is not a solution for the problem, just a workaround that costs a lot of time.
I downloaded the 3mf and try to print it now to give another comparison for the problem.
Will upload the pics once the print is done - about an hour or so…
Edit:
During the print I can see a strange thing.
When the front wall is done the move to the left pillar/post is MUCH slower than the other non-print moves.
I assume that since it is the longest distance the slicer uses it to increase the overall layer time.
With the pillar done, as it is quite short, this slow non-print move is gone as well.
The layer time goes down by quite a good amount.
As you can see by the preview pics the flow rate and speed does not really change that much.
So the main factor here is the loss of time for the layer.
The slim post in the back suffers from over-extrusion caused by the short length of the closed wall loops.
The filament just has nowhere to go and I know of no way to correct this without causing under-extrusion in other areas.
Can’t get a sharp pic from within the printer.
But here the shot from the build in chamber cam:
Will upload some pics of the print once out of the machine.
The result is of acceptable quality to me, all things considered.
For THIS model there does not seem to be any shifting happening, just the usual flow fluctuations.
In all fairness though: I used plain PLA here, not ASA as I had it in the AMS.
The result though should be the same considering the flaws I observe happen with all filaments.
As you can see on the front and back walls there is a well visible line.
In my case going into the model, not outwards.
You can also see that this line more dominant on one end - the END of the wall line, while the start is almost perfect.
The head speeds up and with that the extrusion flow goes down, resulting in this dinted line on the two walls and less dominant on the pillars.
My flow ratio and other calibration factors are good enough.
I can change this line’s appearance from what’s in the pics over being too much at the start all the way to being perfect at the end - but it is impossible to get a consistent line/dint effect.
With the over-extrusion so many users calibrate for this line would poke out - mostly at the start of it while towards the end it looks almost flush.
Without being able to adjust the PA settings I see no way for a user to get rid of these effects.
For the print I used lightning infill, 2 walls as the only change from the standard 0.2mm profile.
The print speeds for my hotend are increased evenly to result in a flow rate of no higher for combined infill and not exceeding 450mm/s for most print moves.
Outer wall is printed at 340mm/s, inner wall at 500mm/s.
