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Nozzle touches bed during Auto Bed Leveling calibration

Posted by Hauser 
Nozzle touches bed during Auto Bed Leveling calibration
May 11, 2018 11:32AM
Hi all,

Today I did something I wanted to do for a long time and that is, check whether or not my auto bed leveling works ok. I wanted to do that because during printing I never noticed the Z-axis moving. I'm aware that that could be because of the bed being already well leveled, I just wanted to make sure everything was ok.

I purposely tilted the mirror I use as printing platform adding two M3 screws between the mirror and the heating bed. Then I proceed to print a very small piece just to see what the printed did during calibration. To my surprise, the nozzle touched the mirror in nearly all of the 16 probing spots. It tried to get deeper on the side of the mirror which was higher due to the screws. I let it print to see what happened next. To my surprise, the Z-axis did move this time around, but the nozzle was touching the mirror so nothing could come out of it.

The probe I'm using is a 10mm capacitive probe and the printer is an Anet A6, still with the original board. The firmware I'm running is Marlin 1.1.8 and I'm pretty sure I set up the bed leveling feature correctly. The Z-offset was well calibrated. Previous to this test I printed a small piece and the first layer was quite nice. Aside from noticing a noise when the nozzle was in some area of the bed, which was what made me suspicious in the first place...

Has somebody experienced something similar? Any insights will be appreciated!

Thanks in advance!
Re: Nozzle touches bed during Auto Bed Leveling calibration
May 11, 2018 09:08PM
Could be a lot of things, if the bed is heated it can cause expansion which would do that. Capacitive sensors are also affected by humidity and temperature which could also throw off your auto probe or z offset causing the collision. Also you should try setting z offset when the nozzle is hot because the nozzle can sometimes expand when hot and cause a collision with the bed due to heat expansion. You could also try adjusting the field of the capacitor with the screw on it. There's a lot of variables as to why it's hitting the bed.

Edited 1 time(s). Last edit at 05/11/2018 09:08PM by Fiyero88.
Re: Nozzle touches bed during Auto Bed Leveling calibration
May 18, 2018 01:21PM
thanks a lot for your input and sorry for my delay.

I took into account all that you mentioned and I finally found the problem... which was much more simple that I was expecting. The problem is the offset. While the probe was measuring a given distance, the nozzle was somewhere else a little higher... (falcepalm)

So, what I get from this experience is that bed leveling is useful, but within some ranges, the bed must be leveled already and the auto bed leveling can compensate for punctual irregularities...

thanks again!
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