ABL not working properly

Hey, this is my first post here in the forum as I haven’t found the right solution to my problem yet. I’ve had a Snapmaker 2.0 A350T for over a year and mainly print with it. But for larger prints I have never had a satisfying first layer.
I have spots all over the print bed that are perfect, spots that are too far away from the printing plate and spots that are printed too close. I have recalibrated countless times, from normal ABL to manual bed leveling to ABL with 11 x 11 measuring points. Nothing was successful. In the meantime I have really calibrated everything: E-steps, flow, temperature, retraction, speed, acceleration, linear advance and many other settings in my slicer (Cura). But the first layer is never good enough. In the meantime, I always execute a series of G-code commands at the beginning of the print for automatic leveling, so that it is at least right in the middle. Here is my Cura start code:

M104 S210 ;Set Hotend Temperature
M140 S60 ;Set Bed Temperature
G28 ;home
G90 ;absolute positioning
M109 S210 ;Wait for Hotend Temperature
M190 S60 ;Wait for Bed Temperature
G1029 P7 ;set leveling grid size
G1029 A ;start leveling
G91; relative positioning for Z offset move
G0 Z-1.85; Device specific Z offset, reduce to bring print closer to the bed
G1029 S ;save data
G1029 D0 ;end leveling
G0 Z10; move up 10mm
G90; restore absolute positioning

I have attached a photo of my current print, I have marked the places that are too close (blue), too far away (red) and just right in green.
But where is the problem now? Have I missed something? I’m starting to get the feeling that the printer isn’t using the height map at all. I also use the heigt map of OctoPrint. The variance is not too big: min: -0.05, max: 0.4719 → variance: 0.5219.
Or is it because of Marlin? I have already found a few articles on this on the Internet.
Am I the only one with this problem or does someone already have a solution and I’m missing an important point?
I would appreciate many helpful suggestions!

Thanks!

Luca

There are a few things which influence the first layer.

  • Leveling the hot bed, let it stay on temperature for at least 30min, maybe 60min.

  • Height of the first layer, I use 0.2mm to 0.3mm

  • First layer width, depending of elefant foot I use between 0.4mm to 0.56mm with 0.4mm nozzle.

Your picture seems not so bad but it’s hard to see. In general a bit overextrusion because of too near to the bed would be over printed in the next layers and is not visible on the top of the model.

There is a lot to find in the forum (perfect first layer). If you don’t want to level manual you could shim under the screws of the bed but this would only make sense if you have the Quick swap kit (so it stays there if you do a tool change).

Thanks für your reply!

The print ist finished, I see a bit of underextrusion on the bottom layer, but I don’t understand why my top layer ist over- and underextruded too.
I printed at 0.2 mm layer height with 0.4 mm line width (0.4 mm nozzle).

On the first-layer-problems: Most likely a bed levelling thing. See this thread for guidance!

You need to use the
M420 S
command to turn on the bed leveling mesh for the print. I would probably add it immediately after your G1029 D0 command.

When leveling is done from the touchscreen, it is automatically tuned on, but not when done using the G1029 commands.

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Although in this case I think the advice you’ve been given (to make sure the mesh is activated) is probably a root cause, don’t forget to also look at any pull resistance of feeding the filament. (I say this because your underextrusion all looks like its to one side like maybe the far side of the axis from the spool, when your filament was under more tension.)

I don’t think having the spool just ‘hanging on a rod’ is good enough to provide uniform extrusion, and mount mine on skate bearing arrangements to reduce the rolling friction of the spool so the extrusion gear never really has to fight harder than normal to feed.

Image below, you can see where I’ve added the hubs. The supplied filament holder is inverted at left because I have a shelf above my SM2 A250. The one at right usually has a threaded knob that holds the bearing-mounted-hub in place, but I removed it so you could see better.

(Too little friction can also be an issue if the spool ‘freewheels’ after a tug and you get filament jumping off of it and wrapping the mount rod, but that’s usually only a problem right at the beginning of use of a brand new spool.)

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