Automatic bed level issue

[Vinculum]

Hi all,

I've just finished my build of the Kossel Mini by Johann Rochol's design. The build is (almost) exactly like his and the software is unchanged except for the definition of electronics type, thermistor and LCD.
It runs the auto calibration and can print very well out of the box. But...
The autolevel does it's job but it appears that it doesn't do anything with the measured data. As you can see in the attachment when i print something fairly big its to high near the front (bottom of picture) and digs in the tape at the back. I've tried to raise the bed at the front to compensate but the slope moves with it. That contradicts with my statement that it doesn't do anything with the measured data.
You can also see that near the frontright corner it dips again fairly quickly. Does anybody have an idea what's wrong?

[edward]

I'm not sure you are going to get many responses here as the auto-level feature is quite new and most RostockMAX users run the Repetier firmware, of which the 0.90alpha version does contain an auto-level feature, but not an interpolation one like Johann's Marlin branch.

However, there are a few of us, and I am one. I get a similar result. I've had trouble accurately measuring it, but my suspicion is that I have a geometry error somewhere that causes the effector to tilt a bit. Since my probe is offset (-13,-13), this means that that tiny tilt could cause enough of an error in the reading of the probe and the actual height of the nozzle to give this effect. I've found my probe to be repeatable to (I can't remember exactly) ~0.02mm, so you could see how this would make a difference. And, with 0.2mm or lower layer heights, it doesn't take much to be too thin. Again, I've haven't made very good measurements to test this idea as I am instead in the process of trying to use some offline analysis code to locate the error.

Fingers crossed

How is your printing without the probe enabled (remove the G29 command)?

[Vinculum]

I'm fairly imbarresed right now. I switched marlin branches and Johann changed one of the geometry settings from 145 to 139 and i didn't see it.
So changed it back and now it prints perfect flat. I'm impressed.

[edward]

Ahh crap. And for a moment I thought it wasn't me

Glad you got it working!

[Vinculum]

Haha sorry. The bed level can compensate but only to a certain degree apparently. If the geometry is off to much it can't fix it enough hence the strange results.

[edward]

That the fear that has been confirmed. I'll get it