Auto Bedlevelling – the final part.

So, my printer now has automatic bed levelling. Aren’t I swish!

Following up from my last post about getting the probing working, I’ve now had a bit more of a faff with the printer (pretty much 4 or 5 hours of fettling).

First thing was to upgrade the bed. Rather than the FR4 that came with the printer I’m now using a 326mm glass build surface and a 300mm 220V silicon pad stuck to the stock bed. I did consider putting a post up on how to wire it, then thought better. It’s relatively straightforward but if you need instructions to do it you probably should use a 12/24V system with less chance of killing yourself. </preachy>

Anyway, onto bed levelling. I started off with the bed mounted as low as it would go on the supports. Unfortunately it looks like one of my Z screws is bent, so I had to move the bed up to not mis steps when it’s near the end of the travel. This has meant that (at least until I replace it) I’m stuck with only 375mm or so of Z travel. Not that that’s really a huge inconvenience.

I also needed to play around with where the machine thinks it is after homing. My E3D mount puts the hotend about 8mm in Y and 3mm in X away from where it should have been. As such I have changed my alpha_min & beta_min settings to adjust:

alpha_min -4 
beta_min -11

There is some extra fat in the numbers in order to avoid accidentally printing off the edge of the bed. The max Y travel is also reduced to about 320, so that needed changing as well.

Ultimately my plan is to bolt everything together rigidly and leave it, however, whilst I’m still tinkering I want to do the level every print. A full 49 point grid takes ages (relative to calibration prints), and since the buildplate is already pretty flat (just not level) I’ve decided to use 3 point levelling for now. My config for this is as follows:

leveling-strategy.three-point-leveling.enable true # Set to true to enable the leveling strategy that probes three points to define
 # a plane and then keeps the Z parallel to that plane. This is useful if 
 # your Z plate/bed is not perfectly aligned with your XY gantry
leveling-strategy.three-point-leveling.point1 80.0,80.0# The first probe point (X, Y)
leveling-strategy.three-point-leveling.point2 160.0,240.0 # The second probe point (X, Y)
leveling-strategy.three-point-leveling.point3 240,80.0 # The third probe point (X, Y)
leveling-strategy.three-point-leveling.home_first true
leveling-strategy.three-point-leveling.tolerance 0.03
leveling-strategy.three-point-leveling.probe_offsets 0,0,0 
leveling-strategy.three-point-leveling.save_plane false

This seems to be giving me a good result.

Lastly, I needed to setup Cura to actually level the bed. I put this in my start GCode.

G28 ;Home
G1 X80 Y80 Z10 ;Move the platform to Z=25 & the first probe point
G32; Probe bed level
G1 X0 Y0; back to the corner then prime 5mm
G92 E0
G1 F200 E5
G92 E0

The test print I’ve tried works well, although I think I need to get some anti-backlash nuts as well as the replacement screw, since you can see some artifacts from the bed tramming. Hopefully the boat from china isn’t too jammed up with 11.11 stuff to get me it in a reasonable time!


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