Auto-leveling Questions

Bill Arnold

1974
Staff member
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Thomasville, GA
It looks like auto-leveling is working on my A8 now that I got the firmware updated, etc. A couple of questions:

The default leveling in Skynet is LINEAR but some think BILINEAR is better. What say you?
//#define AUTO_BED_LEVELING_3POINT
#define AUTO_BED_LEVELING_LINEAR
//#define AUTO_BED_LEVELING_BILINEAR

To adjust the offset between the auto-level reading and the actual position of the hot end, is G92 the correct command? How much offset do you use?

Thanks!
 
I left my z offset at 0 in the firmware, then changed it in the menu on the printer, then stored it in the eeprom.

He covers how to figure out the offset in the video below, but I have my sensor mounted about 1/4" above the nozzle, and it picks up the bed when the nozzle is about 1mm away. I then zero (G28), run the auto level (G29, then set the offset after the auto level runs. Basically tell the printer to go to a height of 0 (G1 Z0), then use drop down .1mm at a time until you are touching your paper as you would normally do to calibrate it. I then go to Control>>Motion>>Z offset(?) and adjust that stored number to be the amount (mine is about -.9mm). Then go back up one level in the menu (under Control still) and Store the values in eeprom. You should be able to run G28 and G29 again. I then set Z to 1mm and step down .1mm at a time to verify the offset is still correct.

https://www.youtube.com/watch?v=rP12HVm-aKA
 
I left the firmware settings as they were in Skynet.

I found that Octoprint has a plugin for reading and writing the Marlin eeprom values. When it didn't appear that G92 was doing anything, I began tweaking the Z-Probe Offset value. I have it at -1.62mm now. Test prints are looking pretty good so far. My test probe is about 5-6mm higher than the nozzle. I adjusted the trimmer in the end of the probe until I got consistent illumination of the LED on the glass.
 
Cool. I've been having really good luck with mine since replacing the carriage plate. I did have an adhesion issue the other day, but don't blame the auto level as it was even all the way around. I had decided to play with the temps with the filament I was using and made a bad choice to not run warmer on the first layer. The entire right row of parts pretty much popped loose one at a time over the last few hours of the print. Eventually the spaghetti blob got big enough it knocked my X axis off by about 1mm and ruined the rest of them.

2017-03-03 20.02.15.jpg

Edit: BTW, the linear vs bilinear may need to be changed if you're finding areas of your bed aren't quite printing correctly due to a twisted bed. I'm running linear and minimized my readings to just the 4 corners since my bed seems to be flat now. The x/z axis needs to be parallel to the table also from what I've found, which is easy to do now that you have the dial gauge adapter.
 
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I'll have to look at the higher temp on the first layer and see what happens.

I ran a test cube box and got the best bottom layer ever. Dimensions of the 20x20x20 box came out at 19.98X by 20.02Y by 20.00Z. Not gonna try for anything better - yet!

On the linear vs bilinear, I got the same idea from what I read. Since I'm using glass, I'm pretty sure it's flat so I'll stay with linear. I printed a set of three test squares that are 153mm, 143mm and 133mm, so they cover a lot of territory. They look perfect all around the plate.
 
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