Bed levelling woes
One of the effects I have noticed during testing is that although I now have ABL set up and (seemingly) working, it doesn't seem to be as accurate as I'd expected. I have analysed the mesh and the right side of the bed is slightly lower than the left. By watching the printer I can see that the Z axis is certainly moving during a single layer of a print, so something is clearly happening.
Despite this, the print quality is very poor on the right side, whereas the left is very good.
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| Left side of bed |
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| Right side of bed |
To test this further, I created a test model (I know that there are hundreds, but I couldn't find one which was quite right for what I wanted) and printed that several times. Each time, the right (lower) side of the bed was printing with much poorer quality than the left.
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| My test model |
My first thought was that perhaps my Z steps/mm were wrong and the printer was simply not moving the correct amount. I re-calibrated and tested this twice, but everything seemed OK.
My next thought was that this was due to software endstops. That is, the right side is technically below Z=0, so maybe the firmware was stopping the extruder from moving down sufficiently. This didn't seem logical, but I tested with endstops off anyway and it made no difference. However, on closer examination of the print, it was clear that the nozzle was too close to the bed, not the other way around. At this point, things seemed very weird indeed. Essentially, the ABL was over compensating for the lower side of the bed.
I did some reading around of articles and found at least one on the Marlin Github pages which may match and seemed to imply that it is actually a bug in Marlin. So, it looks as if my planned Marlin upgrade needs to be pushed up the to-do list a little.
Of course, if anyone knows differently, please comment!
I have published the test model on Thingiverse, if it is helpful.
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