Changing Z offset with BLTouch

cbrunnem2

@BoA bed mesh was complete. see below. bed is not heated during this process and is very much room temp. the below mesh is after adjusting things so that the BLtouch triggers at 2.31mm. issue is still present. this time i had to jog to -1.7mm for the nozzle to just start grabbing a piece of paper. below is also my starting Gcode. i did have a z offset of .35mm in cura in my gcode as i was under the impression that was needed for cura but i have since removed it as it appears to make it worse.

lastly, i agree that if i have to babystep so much i should adjust the z trigger... the issue is... as i typed this, i started another print and i had to babystep to -1.4mm to get a good first layer. it seem to change and drift over time.

G91                        ; Relative Positioning
G1 Z-1                     ; Move Z down 1mm
G90                        ; Absolute Positioning
G28 XY                     ; Home XY
M561                       ; Clear any bed transform
G1 X100 Y100            ; Move Probe to middle of bed
G1 Z10 F6000             ; Move Z to 2
G30                        ; Do a single probe
G29 S1     ; Load heightmap (you can use G29 S1 instead)
G1 Z2 F6000             ; Move Z to 2
M572 D0 S0.05 ;

bed mesh.png

BoA

@cbrunnem2 So You changed in config file

G31 P500 X27.6 Y18.7 Z2.31

as 2.31 was reported by G30 S-1 and You need to baby step even more?
If You manually dial to position where Z=0 (nozzle should be just barely touching bed) is that actually the case?

BTW - IMO Z should be homed and bed probed at printing temperature, as that might affect bed shape.
What kind of printer You have?

fcwilt

@cbrunnem2

You are aware that G30 S-1 only yields a correct result if the starting Z position is correct?

Frederick

OwenD

@cbrunnem2
As @fcwilt has alluded to, it sounds a bit like you're procedure may be a little off.

If you are running RRF 3.5 try putting the two attached macros in you macros folder.
Ideally create a folder > 0:/macros/bl_touch/
Then run start_calibration.g

It will step you through the calibration and carry out 10 cycles to determine the correct Z offset.
The result is saved in config-override.g (or you can edit config.g if you wish)

start_calibration.g
calibrate_BLtouch.g

cbrunnem2

@OwenD im trying to run this. my firmware is messed up or something. i am installing.... hopefully 3.5rc1 right now using that blue button at the bottom of this picture.... that i didnt see before....

hopefully this gets rid of the error when trying to run that macro saying i need to be on 3.5 or newer...

cbrunnem2

@BoA i dont run a heated bed as i havent needed to for PLA.

im in the middle of a firmware update BUT if i remember correctly, after getting the bed to grab a piece of paper, i would set that as z=0. if would grab a piece of paper if i moved and came back.

cbrunnem2

@fcwilt i am not sure what you mean exactly but i would only ever run G30 s-1 after homing x/y and after setting z=0 when the nozzle grabs a piece of paper.

Phaedrux

@cbrunnem2 said in Changing Z offset with BLTouch:

my firmware is messed up or something

Try these files

https://github.com/Duet3D/RepRapFirmware/releases/download/3.5.0-rc.2/Duet2CombinedFirmware.bin

https://github.com/Duet3D/RepRapFirmware/releases/download/3.5.0-rc.2/DuetWebControl-SD.zip

fcwilt

@cbrunnem2 said in Changing Z offset with BLTouch:

@fcwilt i am not sure what you mean exactly but i would only ever run G30 s-1 after homing x/y and after setting z=0 when the nozzle grabs a piece of paper.

Setting Z=0, using the method you mentioned, should insure that the Z position at the start of the G30 S-1 is reasonably correct and thus the value reported should be reasonably correct.

Frederick

cbrunnem2

@Phaedrux Thank you. that did it. for whatever reason, whenever i uploaded the zip files, it would fail half way through

cbrunnem2

@fcwilt thank you. i tried the macro above and it reported 2.5mm which is different than the 2.31 i got BUT what is interesting is that it said it would save it in my config.g but didnt... its properly in the config-override.g though.

even further, i still had to jog down the same amount basically as before. the issue is becoming more consistent. its basically me having to jog down to -1.25 to -1.3mm every time including this time. that is still a larger difference than between 2.31 and 2.5mm.

should i just add the 1.3mm to my 2.31mm and call it a day????

as i am writing this, i realized, some of my error is in not zeroing the bed at the correct nozzle temp but that is not 1.3mm of error. my math says its about .1mm of thermal expansion. i can fix that in the future calibrations.

BoA

@cbrunnem2 Can You upload gcode that You are trying to print? Are You sure, there is no offset set in slicer or something?

When You set Z trigger height, home XYZ, and the jog to Z=0. Nozzle should be just touching printbed.
(Home XY, Home Z with probe, then jog to position where Z=0)

fcwilt

@cbrunnem2

You must always set the Z=0 Datum, using a single G30 as a fixed XY location, before creating the height map and before loading the height map to print.

And when determining the G31 Z Trigger Height, by whatever means, you need to use the same fixed XY location.

Some folks like to use a point of the height map grid. I use the center of the bed.

And you need to be sure baby-stepping and mesh compensation are disabled when doing either of the above.

Frederick

engikeneer

@cbrunnem2 to add to what @fcwilt had said, you should also reset your z=0 datum after performing bed levelling (and before loading/creating your heightmap).
When it does the bed levelling, it can shift the datum depending on how level your bed is. Hence the need to rehome z with your z probe at the same xy position

cbrunnem2

@BoA i appreciate your help and everyone elses. Thanks. Gcode below. Just the start.

;FLAVOR:RepRap
;TIME:2435
;Filament used: 3.38708m
;Layer height: 0.25
;MINX:48.526
;MINY:92.173
;MINZ:0.25
;MAXX:84.309
;MAXY:127.954
;MAXZ:25.5
;POSTPROCESSED
;Generated with Cura_SteamEngine 5.2.2
T0
M104 S230
M109 S230
M82 ;absolute extrusion mode
G91                        ; Relative Positioning
G1 Z-1                     ; Move Z down 1mm
G90                        ; Absolute Positioning
G28 XY                     ; Home XY
M561                       ; Clear any bed transform
G1 X100 Y100            ; Move Probe to middle of bed
G1 Z10 F6000             ; Move Z to 2
G30                        ; Do a single probe
G29 S1     ; Load heightmap (you can use G29 S1 instead)
G1 Z2 F6000             ; Move Z to 2
M572 D0 S0.05 ;
M83 ;relative extrusion mode
G1 F300 E-0.25
;LAYER_COUNT:102
;LAYER:0
M107
G1 F600 Z0.5
G0 F2400 X57.32 Y94.657 Z0.5
;TYPE:SKIRT
G1 F600 Z0.25
G1 F300 E0.25
G1 F600 X57.994 Y94.278 E0.03215
G1 X58.844 Y93.849 E0.03958
G1 X59.493 Y93.562 E0.0295
G1 X60.145 Y93.305 E0.02914
G1 X60.828 Y93.068 E0.03006
G1 X61.356 Y92.904 E0.02299
G1 X62.223 Y92.669 E0.03735
G1 X63.006 Y92.501 E0.03329
G1 X63.992 Y92.333 E0.04158
G1 X64.7 Y92.253 E0.02962
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G1 X74.047 Y126.246 E0.0481
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G1 X56.075 Y95.457 E0.02766
G1 X56.545 Y95.137 E0.02364
G1 X57.32 Y94.657 E0.0379
G0 F2400 X57.516 Y95.006
G1 F600 X58.305 Y94.562 E0.03764
G1 X59.383 Y94.035 E0.04989
G1 X60.292 Y93.677 E0.04062
G1 X61.076 Y93.409 E0.03445
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G1 X82.914 Y115.896 E0.03029
G1 X82.611 Y116.671 E0.0346

BoA

@cbrunnem2 Seems Your start g-code is a little messed up. Why not homing Z, but probing?
Seems this one will not execute home.z or home_all nor bed.g at all (might be wrong, but looks that way for me).

Probing and all other stuff is on purpose in printer files, so You can just execute G28 and G32.

cbrunnem2

@fcwilt i just powered on my printer. when its off, the bed sags a bit so i immediately homed xyz. height map looks good. babystepping was always at 0

i did the following commands:
G1 x100y100
g29 s2
G1 z0 (stepped down till nozzle is on bed)
G92 z0
g30 s-1 put that number in config.g under the g31 line
restarted board
homed xyz
G1 x100y100
g29 s2
G1 z0 (stepped down till nozzle is on bed)
g92 z0
g1 z10
g1 z0 (nozzle is still on bed)
G30 (it stops at 3.1mm which is what i have in g31)
g1 z0 (nozzle is too high.... by -.85 which ironically, is the about what the math would say my previous number should be at -2.31)

im at a lose here.... what am i doing wrong

cbrunnem2

@BoA should i be doing a whole bed mesh at the start of every print? is that what you are saying?

might be worth it if i can figure out this problem as a hole. check my last response. with the current issue, id be wasting so much time probing hte bed just to have to babystep or ruin a print.

cbrunnem2

@BoA also, there is a g28 xy so those axis get homed. G30 at x100y100 should mean my heightmap is valid to load and use?

cbrunnem2

i added a G30 before G29 in my bed.g to see if that would help. it did not. i assume this is good practice and should be left?