Changing Z offset with BLTouch

[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
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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
G1 X65.726 Y92.18 E0.04276
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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
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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?

[BoA]

@cbrunnem2 I think You created a little bit of chaos in the files trying to solve the issue. Let's sort things out.

1. make sure homex.g and homey.g do only X and Y and Y homing, and nothing more.
2. make sure homez.g does only homing Z using probe. For example:

G91
G1 H2 Z5 F12000    ; lift Z relative to current position
G90                 ; absolute positioning
G1 X100 Y100 F12000
M558 F1200
G30                 ; home Z by probing the bed
M558 F120
G30                 ; home Z by probing the bed

3. make sure homeall.g is homing X and Y and calls homez.g For example:

G91                 ; relative positioning
G1 H1 X5.0 Y5.0 F1200
G1 H1 X-260 Y-221.5 F3000
M98 P"homez.g"
G90

After that calling G28 should home all axes, and going to Z=0 position like G1 X100 Y100 Z0 results in nozzle just barely touching the bed.

Next step would be to set bed/gantry leveling using bed.g
BTW - make sure

M671 X200:200 Y-133:567 S15

is correct. This seems a little strange looking where Your bed.g probes for bed/gantry leveling.

G30 P0 X5 Y100 Z-99999     ; probe near a leadscrew, half way along Y axis
G30 P1 X225 Y100 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors
G28 Z

should be enough, use screws coordinates that are correct for Your printer.

After that calling G28 and G32 should result in homing all axes and pribing bed in 2 (or more) points and bed leveled and re-homing Z axis.

Soo... in Your startup gcode in slicer You should have

G28
G32

sequence

If Z trigger height is set correctly, that should give You correct-ish first layer without babystepping.

After that works, You can call G29 S0 to probe the bed and save heightmap and after G32 add G29 S1 to startup gcode

[BoA]

@cbrunnem2 For reference my startup code in prusa slicer

G90 ; use absolute coordinates
M83 ; extruder relative mode
M144 S1
M140 S[first_layer_bed_temperature] ; set bed temp
G10 P0 R120 S[first_layer_temperature_0]
M116 H0
G28 ; home all without mesh bed level
G32 ; gantry leveling
G29 S1; mesh bed compensation

[fcwilt]

@cbrunnem2

So when you do that single G30 the nozzle is touching the bed?

What is the behavior you see?

Frederick

[cbrunnem2]

@fcwilt when I use g30, the bltouch triggers and stops the bed. if I then use g1 z0, I then have to move the bed up manually till the bed touches. it's about .7mm now.

[fcwilt]

@cbrunnem2 said in Changing Z offset with BLTouch:

@fcwilt when I use g30, the bltouch triggers and stops the bed. if I then use g1 z0, I then have to move the bed up manually till the bed touches. it's about .7mm now.

Keep tweaking the G31 setting until Z=0 results in the nozzle just touch the bed.

Because my printing surface is not hard like glass or metal I use Z=1 as my test position and have a 1mm thickness gauge that I use to check the gap. Otherwise the nozzle might just make an indent in the surface when I'm tweaking G31.

Frederick

[cbrunnem2]

@BoA Thank you for your response.

1. my homex/homey are exactly as you mention
2. i will fix my homez. i have no M558 calls in my homez. could be the issue? see below for my homez current gcode.
3. will fix my homeall file as well.
4. i will double check my M671 values. the printer bed is actually 400mm x 400mm but i am only currently using a small portion so i lowered my bed mesh size to get better results and speed things up. i believe the Y positions are correct. i know the x positions are correct.
5. should i do the bed leveling more than once? when reseting my board or powering it on, my bed has to be releveled as it sags a bit. typically 2 bed levels gets it super close.
6. on your last comment about doing a G29 S0... i should do that after fixing all of my homing issues and before a print right?

; homez.g
; called to home the Z axis
;
; generated by RepRapFirmware Configuration Tool v3.2.3 on Wed Jul 21 2021 18:08:02 GMT-0400 (Eastern Daylight Time)
G91             ; relative positioning
G1 H2 Z5 F3600  ; lift Z relative to current position
G90             ; absolute positioning
G1 X100 Y100 F3600 ; go to first probe point
G30            ; home Z by probing the bed
G32 ;
g30 s-1;
G29 s1;

[BoA]

@cbrunnem2
Ad. 2 - I have M558 just to change probing speed - first fast pass for less acurate, and second slower for better accuracy
Ad. 4 - The closer to leadscrews You probe the better the results will be (more accurate). This has nothing to do with area used for printing or mesh leveling. It is just to make sure bed.g will set left and right bed motors correctly too keep bed parallel to the gantry. G32 is not the same feature as mesh bed leveling. G32 makes sure the bed and gantry are parallel to eachother. Mesh leveling (G29) compensates for bed beeing not perfectly flat.
Ad. 5 - In general it should be fine doing it once, but nothing wrong with doing it more than once
Ad. 6. for homez.g put only homing z there.

; homez.g
; called to home the Z axis
;
; generated by RepRapFirmware Configuration Tool v3.2.3 on Wed Jul 21 2021 18:08:02 GMT-0400 (Eastern Daylight Time)
G91             ; relative positioning
G1 H2 Z5 F3600  ; lift Z relative to current position
G90             ; absolute positioning
G1 X100 Y100 F3600 ; go to first probe point
G30            ; home Z by probing the bed

that is enough for it.

Then in slicer You have a startup g-code, where You should have:
homing - G28
bed leveling - G32 (this will execute bed.g with probing next to leadscrews, and re-home Z)
mesh compensation enabled G29 S1

Bed probing before each print depends on how stable geometry Your bed has.