strange extruder skipping steps

Even when printing solid infill when there is quite large amount of plastic extruded my extruder is coping well, no problems. But, when print gets to a first solid layer on top of infill, which is shown in prusa slicer as bridging

extruder keeps skipping steps. This bridging layer is printed at the same speed as infill (infill prints with no problem)

For some reason prusa slicer shows much higher volumetric flow for bridging than for perimeters or infill.

I don't really understand this as flow rate for bridging in prusa slicer is set to 1, which I presume means that it is the same as for perimeters and infill. Why speed and flow rate are the same, but volumetric flow is much higher? I have no idea how it is possible.

My current marlin 2.0 settings related to extruder are:

#define DEFAULT_ACCELERATION 600
#define DEFAULT_RETRACT_ACCELERATION 1000
#define DEFAULT_TRAVEL_ACCELERATION 1000
#define DEFAULT_MAX_FEEDRATE { 300, 300, 8, 25 }
#define DEFAULT_MAX_ACCELERATION { 1200, 1200, 200, 10000 }
#define DEFAULT_EJERK 5.0

I am planning on tweaking the extruder settings. Should I start by reducing the EJERK or the acceleration? Is there something that I should try before messing up with Marlin settings?

I am running LV8729 set to almost 800mA on my Anet A6 stock motor and extruder. My LV8729 came with 220 resistors and I have set Vref to 0.87V

Hi, I'm not sure if 800mA is enough. I'm not sure if it depends on your stepper driver, but I think not. My Delta printer stepper driver (TMC2208) had to be set to at least 1000mA to stop it from losing any steps during printing. It runs really well now though.

Still this doesn't answer your problem, I am having the same kind of issues with my MendelMax printer for some obscure reason and that one uses A4988 that are set to high mA. I can extrude as much as I want manually, but during printing it somehow loses steps. For me I have planned to completely overhaul the electronics for my machine such as shortening the stepper cables to the minimum needed because they are now all 1M long. I think this is wasting unnecessary amounts of power (DC 12v) and I hope this might help me solve this problem by rebuilding the electronics and basically rebuilding every aspect of the machine. But first I have to finish the machine I'm still building harhar.

Anyway, try a higher amperage and see if that helps. 800mA on an extruder stepper is still kinda low.

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http://www.marinusdebeer.nl/

I have done some more testing today. My extruder can comfortably extrude up to 420mm/min. I can even go above 1000mm/min but I think filament is slipping at such high speed, but there is no skipping from the extruder. I printed the same little test cube as in the pictures above with the linear advance off (K value set to 0) and it printed no problem with no skipping from the extruder. With linear advance on, extruder just skips at the end of each line of the first solid layer on top of infill In this first solid layer (which is treated as bridging in prusa slicer) lines are not next to each other. It seams that extruder is printing long line then skips at the end of it when it changes direction to print a very short section and then skips again on another change in direction just before printing another long line. During long line printing there is no skipping.

When linear advance is on my K value is 0.12. That's the value I have got after running Linear advance K value calibration

maybe it would be helpful to see pictures of what the problem is on your printed object.
additionally maybe you should ad your slicer config bundle. There are more parameters that matter for extrusion.

I think I have fixed the problem. I have done 2 changes in marlin.

1) Changed JUNCTION_DEVIATION_MM from default to 0.04 which seems to be the correct value for my acceleration of 1000 according to this: [blog.kyneticcnc.com]

2) I have also set #define MINIMUM_STEPPER_PULSE 0 (as I am running TMC2208 on XYZ and LV8927 on extruder)

With this 2 changes in marlin no more extruder skipping steps on direction changes. At least not during first few quick print tests. I hope I am not celebrating too soon and that it will stay that way.