BLTouch and UBL - bed skew and bad adhesion?

beata

Everything appears to work, bed is leveled at corners but topography map is high on one side and the validation pattern doesn't stick to the bed very well. I'd like a look over my calibration procedure before I go further.
I'm curious why the map is skewed when the corners are (supposedly) level. Something wrong with the mount?

I'm starting clean (M502 reset) and measured probe X and Y offsets previously. BLTouch and UBL are enabled in the configuration. The gantry is connected to the Z_MIN endstop and the BLTouch to the Z_MAX. Center homing is enabled. Control is through the Arduino serial monitor. LCD controller is disconnected.

After homing to Z_MIN  I move to each corner and adjust the bed to the nozzle using the thumbscrews, with a 0.05mm feeler gauge. I re-home (bed center and Z0) and measure with feeler gauges. My bed is approx 0.25mm lower in the middle. This fits with using manual mesh leveling previously. I then raise the nozzle and move the sensor to center position. I deploy the probe and then lower by 0.1mm until the probe triggers. I set this offset into M851 and run the mesh probe and print the validation.

code:
G28
G1 Z5
G1 X4 Y1; X304 Y1; X304 Y301; X4 Y301
G1 Z0
(adjust thumbscrews with 0.05mm feeler gauge)
(...)
G28
G1 Z0
(measure nozzle gap with feeler gauges. It's consistently 0.25 or 0.30)
G1 Z10
G1 X138 Y110
(my mount puts the probe at 14, 42)
M280 P0 S10
G91
G1 Z-0.1
(repeat until trigger)
G90
G1 Z10
M280 P0 S160
M851 Z3.2
M500

G29 P1
(wait a while)
G29 S1
G29 T
(here I have a global offset. Writing this I see I may need to negate the offset in the M851 command. Instead I zero the offset)
G29 P6 C-6.4
G29 S1

(make sure I have a clean bed first, of course!)
G28
G26 C B70 H205 P0 L0.1

(...)
And here the filament doesn't stick well to the bed.

And don't forget the bed topography report:
(the 0.667 is one of the bed clips)
Bed Topography Report:

(0,8)                                                           (8,8)
(9,303)                                                        (303,303)
 -0.030   -0.050   -0.045   -0.031   -0.024    0.036    0.094    0.184    0.271 
 
 -0.053   -0.082   -0.098   -0.073   -0.034    0.046    0.089    0.173    0.667 
 
 -0.083   -0.107   -0.120   -0.077   -0.047    0.014    0.111    0.179    0.286 
 
 -0.089   -0.127   -0.114   -0.060   -0.031    0.045    0.121    0.179    0.295 
 
 -0.099   -0.116   -0.093   -0.048   -0.018    0.048    0.122    0.171    0.277 
 
 -0.062   -0.076   -0.058   -0.009  [-0.000]   0.066    0.115    0.172    0.367 
 
 -0.012   -0.019   -0.034    0.023    0.068    0.083    0.135    0.174    0.280 
 
  0.045    0.050    0.052    0.066    0.083    0.115    0.151    0.193    0.325 
 
  0.148    0.143    0.155    0.159    0.147    0.161    0.171    0.213    0.309 
(9,42)                                                            (303,42)
(0,0)                                                             (8,0)
ok P15 B3

Der_Muck

M502

M500

M501

G28

M851 Z3.2     ; your z-offset value

G29 P1

G29 T

G29 S1

G29 F4

G29 A

M500

G1 Z15.0 F6000

G1 Z0.20 Y0 X0 F6000

G92 E0.0 ; reset extruder distance position

G1 X60.0 E9.0 F1000.0 ; intro line

G1 X100.0 E15 F1000.0 ; intro line

G92 E0.0 ; reset extruder distance position

Try that but ofcause I dont know if your slicer adds the pre heat code itself. My skript works well with S3D (the M851 is add from your code before)

If it stays the same, try to lower the M851 valve till you get a nice first layer.

Laser8302

Is your nozzle too far away from the bed when it starts the validation? Have you printed successfully with 70c bed and 205c extruder temp with the filament in your printer?

The z offset is critical. 3.2mm seems a bit large but I dont know what mount you are using. If it's not sticking I'd either try different temperatures, or a different z offset. Next up would be to use a different layer height. 0.1mm is a bit small for a first layer, maybe try 0.12?

I think a better offset method would be to use a 0.10mm or 0.20mm feeler gauge under the nozzle, turn off the soft endstop with M211 S0, see if you can get it to +/-0.01mm by using G90, G1 z-0.01 to move it down after you move it up 0.1mm when the feeler gauge starts catching.

Watch that your gantry isn't skewed by the z min endstop block.

beata

Frustratingly, I was able to print several objects (copies of drag chain segment, so same gcode), then the print stopped sticking.
I'm using https://www.thingiverse.com/thing:3078550 as the bltouch mount.

Laser8302

I guess I don't understand why use the ZMIN endstop of the gantry, but also have a touch probe?
If you are using the ZMIN I don't think you need an M851/Z-offset at all since you are using the Z-MIN endstop still?

I guess you would need it for identifying the mesh levels.

How old is the filament you are using? Is it dry?

Der_Muck

Ohhh I overread that, @Laser8302 your right, why is there a need for a Zmin endstop, I dont get that at all.

Laser8302

One more problem after reading again. After a G28 command, mesh bed leveling is turned OFF so it might not use the mesh to validate the mesh???
Do:
G28
M420 S1 ; turns on mesh
G26 C B70 H205 P0 L0.1