Auto Bed Leveling Issues

I think I might be having some leveling issues using the BLTouch. It appears as if it's not working. I have Marlin 1.1.8 on a D-Bot CoreXY machine. The reason it caught my attention is that I printed a sacrificial tower off to one corner for a print this evening and it took 2 layers or so before the first layer would lay down on the bed while the center print started at layer 1. I started watching the Z position during the print head moves and it never changes from the center to the corner! When I say that I mean I am watching the LCD and the Z-coords stay the same across the print. It should be changing??? That tells me something isn't right. I am using a BLTouch and have adjusted my z-offset using this video, [www.youtube.com] The z-offset and the bed leveling G29 are done with both the nozzle and bed hot.

Here is my S3D start script,

M280 P0 S160 ; BLTouch alarm release

G4 P100 ; delay for BLTouch

G28 ; home

G29 ; auto bed leveling

G92 E0

G1 Z0.1 F1000

G1 X8.0 F2000

G1 Y280.0 E4.0 F1000.0 ; prime

G1 Y240.0 E8.5 F1000.0 ; prime

G92 E0



When I do the bed leveling here are the z coords it shows

11.31/11.32----11.23/11.23----11.09/11.1----10.99/11.01----11.01

11.25/11.26----11.29/11.29----11.33/11.33----11.06/11.06----11.05/11.05

11.25/11.25----11.14/11.13----11.11/11.11----11.08/11.09----11.1/11.1

11.21/11.21----11.23/11.23----11.07/11.08----11.11/11.1----11.07/11.09

11.12/11.13----11.23/11.23----11.18/11.17----11.16/11.15----11.22/11.21


Upon starting a print the BLTouch does go through a 5x5 grid. EEPROM is active. Suggestions?

Edited 1 time(s). Last edit at 06/20/2019 12:15PM by SmithSith.

Ran an M48 and in one corner the standard deviation was .005, the opposite corner .001. So the BLTouch is reading and the deviations are good. Probably loser on the first corner because I loosened up the rail to make sure it wasn't too tight.

I need someone to verify if Z coords even reflect the autobedlevel changes at all...It might not even supposed to show on the LCD screen.

However, i did a G28, G29 from Ponterface and got this.
0 +0.065 +0.156 +0.067 +0.071 +0.134
1 +0.086 +0.052 -0.026 -0.007 -0.009
2 +0.125 +0.016 +0.000 -0.037 -0.020
3 +0.120 +0.151 +0.184 -0.064 -0.051
4 +0.184 +0.094 -0.057 -0.132 -0.134

I then sent M500

I then started a print using
G28
M420 S1

This time it did print in the corner somewhat correctly, but I need to verify above before I can say that worked. Maybe I need to do an M500 after the G29 on my S3D prints? I know I don't HAVE to do a g29 every time, but it doesn't take too long.

The Z coordinates shown in the LCD will not reflect the bed leveling at all - so for example if you move from left to right on a tilted bed the head will move up or down to compensate but the displayed Z value will be constant.

If you have enough flash space available on your control board you can try enabling G26_MESH_VALIDATION - that adds the G26 gcode that will print out a pattern on your bed showing all the mesh points so you can verify that they are being corrected appropriately.

What bed leveling method are you using? Bilinear or UBL?

Another possibility is code like:

G0 X0 Y0 Z1
G0 X220 Y0
G0 X220 Y220

(for a 220x220 bed) and observe your Z leadscrew to see if it moves as the nozzle moves. If it does, then the corrections are being applied. This will at least serve as a "smoke test" but it's still useful to use G26 to make sure the mesh is correct.

Edited 2 time(s). Last edit at 06/20/2019 05:48PM by MMcLure.

Thanks for verifying that. Something wasn't sticking though with how I was doing it to begin with. So I originally set this at the beginning of every print.

M280 P0 S160 ; BLTouch alarm release
G4 P100 ; delay for BLTouch
G28 ; home
G29 ; auto bed leveling

However, as I said the corner didn't print right. I removed all of that from my S3D code and did the following:
From Pronterface
G28
G29
M500

Then in my S3D code
G28
M420 S1

I think downloaded a bed level stl from Thingiverse and the entire print across the bed to all 4 corners and across diagonally printed correctly. You can look at post 3 above to see that the mesh for that front left corner is higher, which would have made my print closer to the bed and the nozzle wouldn't lay down filament until it moved off of the bed. It also shows my 0.00 at the center that proves my Z-Offset is there and holding. Something in the way I was running that leveling code from S3D originally just isn't working. The only thing I can think of is following the G29 with an M500 and M420 S1...but from BLTouch's website and what I've read...that shoulnd't be necessary?

Quote
SmithSith
The only thing I can think of is following the G29 with an M500 and M420 S1...but from BLTouch's website and what I've read...that shoulnd't be necessary?

I think it depends on what leveling method you use. The good thing is that now that you have the mesh saved you can probably avoid having to regenerate it each time and just need M420 S1 at the start of the print.