BL touch seems doesn't adjust

fcwilt

Hi,

Perhaps DC42 will jump in here with some feedback.

I've wondered the same thing. I don't see movement on the Z axis where I think I should.

Maybe there are some conditions where there is no compensation.

Did you create the map with the bed hot? My "bed" is a sandwich of aluminum plate, glass and a build surface. I let it heat up at least 15 minutes before creating the map.

Frederick

felt342

@fcwilt yes seems strange. Moves what I have in the middle of the bed also a bit jerky on the Z-axis, expecting them a bit smoother.

I do probing with all heaters disabled. I didn`t saw big differences in the heightmap with cold and 80C heated, so left with a cold bed for all probings.

Phaedrux

Please share your homeall as well, though your start script only uses home X and Y and then you manually home Z with a G30, so that should be ok, but still post your homing files so we can see what all is happening.

Do you use G32/bed.g at all? If so, post that as well.

Things to try:

Send M376 H0 to ensure the mesh isn't being tapered off at all. If the bed and mesh is very flat and there is some taper applied, the amount of movement may end up being below the movement resolution of your Z axis.

How are you running G29? How are you homing first? Are you doing it with the bed hot? Same goes for measuring the Z probe trigger height.

You may also want to reduce your probing speed. 600mm/min is a bit fast for the Bltouch. Best accuracy and repeatability around 60mm/min.

Make sure your XYZ offsets are correct. https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#Section_Calibrate_the_Z_probe_trigger_height

Your trigger height seems quite low. When mounted as suggested by Antclabs the BLTouch body should be ~8mm above the nozzle tip which would lead to a trigger height of ~2mm. Also ensure the Bltouch is as vertical as possible and as close to the nozzle as possible, preferably inline with the nozzle in at least one axis, preferably x.

felt342

Hi @Phaedrux

Homing files:

; homeall.g
; called to home all axes

; Home XY for Z homing
;
G91                     	; relative positioning
M913 X50 Y50	 		; set X Y motors to 50% of their normal current for homing
G1 S1 X-321 Y272.5 F4000   	; course home X or Y
G1 S1 X-321 F4000              	; course home X
G1 S1 Y272.5 F4000              	; course home Y
G1 X2 Y-3 F4000             	; move away from the endstops
G1 S1 X-321 F200           	; fine home X
G1 S1 Y272.5 F200               	; fine home Y
M913 X100 Y100	 		; set X Y motors to 100% of their normal current

; Z homing section follows
;
G90				; absolute positioning
G1 X146 Y106 F4000		; Move x and Y axis over to bed center so probe is on top of bed

; Set lower speeds for homing
M566 Z5			; Set maximum instantaneous speed changes (mm/min) (Jerk)
M203 Z400			; Set maximum speeds (mm/min)
M201 Z100	 		; Set maximum accelerations (mm/s^2)

; Probe the bed
;
M558 A1 F350			; Set single probing at faster feed rate
G30 				; Do a single probe to home our Z axis
M558 A10 F100			; Set tripple probing at slower feed rate
G30				; Probe again to get a more accurate position

; Set normal speeds again
M566 Z400			; Set maximum instantaneous speed changes (mm/min) (Jerk)
M203 Z600			; Set maximum speeds (mm/min)
M201 Z400			; Set maximum accelerations (mm/s^2)

; Move X and Y back Home
;
G1 X0 Y0

; homex.g
; called to home the X axis

G91               		; relative positioning
M913 X50	 		; set X motors to 50% of their normal current for homing
G1 S1 X-321 F4000 		; move quickly to X axis endstop and stop there (first pass)
G1 X3 F4000       		; go back a few mm
G1 S1 X-321 F200  		; move slowly to X axis endstop once more (second pass)
M913 X100	 		; set X motors to 100% of their normal current

; homey.g
; called to home the Y axis

G91               		; relative positioning
M913 Y50	 		; set Y motors to 50% of their normal current for homing
G1 S1 Y272.5 F4000 		; move quickly to Y axis endstop and stop there (first pass)
G1 Y-3 F4000       		; go back a few mm
G1 S1 Y272.5 F200  		; move slowly to Y axis endstop once more (second pass)
M913 Y100	 		; set Y motors to 100% of their normal current

; homez.g
; called to home the Z axis
;
; generated by RepRapFirmware Configuration Tool v2.1.4 on Thu Jan 02 2020 22:17:48 GMT+0100 (Central European Standard Time)
G91                 ; relative positioning
G1 H2 Z0 F8000     ; lift Z relative to current position
G90                 ; absolute positioning
G1 X146 Y106 F15000 ; go to first probe point
G30 F180                ; home Z by probing the bed

; Uncomment the following lines to lift Z after probing
;G91                ; relative positioning
;G1 H2 Z0 F250      ; lift Z relative to current position
;G90                ; absolute positioning

And this how I do probing everything on cold bed, I took it from betruedk blog:
First home XY - position nozzle on the middle of the bed, then issue G30, move bed until its touching the bed, reset Z0, moving a bed down 10mm and last
G30 S-1 to get the Z offset. Setting it in config.g > restart > home all and start probing by pressing the button in the dialog:

This is my setup for BL touch I do have 8mm from the casing of BL touch till the tip of the nozzle - that seems correct?

And this is how it's mounted:

Now I start thinking, maybe my 3D model of BL touch is wrong? And from there is wrong height position

Phaedrux

@felt342 said in BL touch seems doesn't adjust:

Now I start thinking, maybe my 3D model of BL touch is wrong?

There's always a danger of using CAD for real world measurements. Best to verify.

The rest of your homing files look good. I see you're lowering the speed for probing, which is good, but the G29 will still be using your speed from config.g

You should also probably change your start gcode to just use G28 to call homeall instead of G28 XY and manually homing Z.

felt342

@Phaedrux

Hm yes, I did check very roughly measurement from BL touch casing till nozzle tip, it looks like 1.1cm... And I did also check the 3D model of BL touch it is shorter than installed one... This is there my measurements got wrong, the model was from Thingiverse downloaded a long time ago, and I just blindly used it...
However, I do have difficulty to measure it precisely how much I need to compensate is there any suggestion here? The nozzle tip and BL touch center is 45mm apart, quite hard to get it precise.

Phaedrux

I just measured like this. Maybe with your mount it's not that easy.

It says 8mm +- 0.5mm so there's a bit of range. And even a bit out of that might not matter too much. But I think it's more important than most people realize.

felt342

@Phaedrux

Hi,

Yeah that is harder with my way of mounting... But I will figure out something
What do you think is it better to have it a bit lower than a bit higher?

Phaedrux

@felt342 said in BL touch seems doesn't adjust:

What do you think is it better to have it a bit lower than a bit higher?

Well it's a bit of a balancing act. If you go too low, you risk the pin getting caught on the print if it curls. If you go too high, you risk the nozzle hitting the bed before the pin triggers.

felt342

@Phaedrux

Well, I did turn off mesh leveling during printing, only keep BL touch for Z homing as I don't have time to play with BL touch now.
And there is a result:

BL TOUCH:

Without:

I am quite happy what I am getting without Auto bed leveling, the top box is not squished enough, but I guess 0.050mm shim under right corner should do the job, guess leave it for now and maybe will get back to BL touch different time

I did print ABS with 100C degrees heated bed and 50C chamber, to make sure the bed is properly expanded.

Phaedrux

If your bed is flat enough that you don't need mesh compensation count that as a win.