Nozzle gets smashed against the bed

fcwilt

Hi,

The trigger height is simply the Z position when the probe triggers.

You can execute the a G30 S-1 command to show what the trigger height is, assuming the probe is working.

Frederick

Phaedrux

3.2mm seems quite high for a BLTouch. When mounted correctly as described in the BLTouch install instructions the probe body should be 8mm above the nozzle tip. This should result in a trigger height of ~2mm.

Here is how you find your trigger height:
https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#Section_Calibrate_the_Z_probe_trigger_height

And general instructions for the BLTouch: https://duet3d.dozuki.com/Wiki/Connecting_a_Z_probe?revisionid=HEAD#Section_BLTouch

Phaedrux

@MJCT said in Nozzle gets smashed against the bed:

M558 P9 H0.5

Your dive height is also WAY WAY too low. H0.5 is telling the firmware to only raise the nozzle by 0.5mm before trying to probe the bed. That's not going to end well. H5 for 5mm is far more reasonable to be safe. After you have things working it can be lowered slightly to reduce the amount of needed travel, but it's still going to need to be more than your trigger height. Think about it. You need to raise the probe high enough above the bed for the pin to drop down below the nozzle.

Phaedrux

@MJCT said in Nozzle gets smashed against the bed:

G31 P500

Try P25 instead. This is the trigger sensitivity.

MJCT

@fcwilt said in Nozzle gets smashed against the bed:

mmand to show what the trigger height is, assuming the probe is working.

Tried G30 S-1 before posting. It didn't worked very well, but I thought that it was due to a previous mistake, and I still believe that the problem is more upstream.

fcwilt

@MJCT said in Nozzle gets smashed against the bed:

@fcwilt said in Nozzle gets smashed against the bed:

mmand to show what the trigger height is, assuming the probe is working.

Tried G30 S-1 before posting. It didn't worked very well, but I thought that it was due to a previous mistake, and I still believe that the problem is more upstream.

In what way did it not work?

Have you made the setting changes that others have mentioned?

Frederick

MJCT

@Phaedrux thanks (again)

I will try your’s several advices tomorrow. Unfortunately I don't have the printer here right now

MJCT

@fcwilt
It said that the probe didn’t touch the bed, if I’m not mistaken
I didn’t try the settings changes because I was commuting home. I will try it firs thing in the morning

fcwilt

@MJCT said in Nozzle gets smashed against the bed:

@fcwilt
It said that the probe didn’t touch the bed, if I’m not mistaken
I didn’t try the settings changes because I was commuting home. I will try it firs thing in the morning

Well the dive height setting likely caused that.

Frederick

MJCT

Ok, I followed yours instructions and it all worked fine. G30 S-1 gave me 0.212 0.213 0.213 Pretty consistent, right?

Than run a Mesh Compensation that showed -0.008 to 0.138mm. I guess I can live with that, at least for now.

Then I started a print. A test cube sliced on Cura 4.2.1 with REPRAP on settings.

The problem is that it starts to print far above from the bed. The tool position in the status show Z 0.30 which should be all right because my first layer in the slicer was 0.3mm. Then I tried the same cube with 0.2mm in the first layer. The status shows Z 0.2 but again it prints far above the bed.
What I’m doing wrong this time?

; Configuration file for Duet WiFi (firmware version 2.03)
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool v2.1.3 on Thu Nov 28 2019 16:04:13 GMT+0000 (Hora padrão da Europa Ocidental)

; General preferences
G90 ; send absolute coordinates...
M83 ; ...but relative extruder moves
M550 P"AA 300x300x600" ; set printer name

M669 K1 ; select CoreXY mode

; Network
M551 P"AA" ; set password
M552 S1 ; enable network
M586 P0 S1 ; enable HTTP
M586 P1 S0 ; disable FTP
M586 P2 S0 ; disable Telnet

; Drives
M569 P0 S1 ; physical drive 0 goes forwards
M569 P1 S1 ; physical drive 1 goes forwards
M569 P2 S1 ; physical drive 2 goes forwards
M569 P3 S0 ; physical drive 3 goes backwards
M584 X0 Y1 Z2 E3 ; set drive mapping
M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
M92 X80.00 Y80.00 Z4000.00 E96.94 ; set steps per mm
M566 X900.00 Y900.00 Z12.00 E120.00 ; set maximum instantaneous speed changes (mm/min)
M203 X6000.00 Y6000.00 Z180.00 E1200.00 ; set maximum speeds (mm/min)
M201 X500.00 Y500.00 Z20.00 E250.00 ; set accelerations (mm/s^2)
M906 X1750 Y1750 Z1750 E1750 I30 ; set motor currents (mA) and motor idle factor in per cent
M84 S30 ; Set idle timeout

; Axis Limits
M208 X10 Y10 Z0 S1 ; set axis minima
M208 X300 Y300 Z585 S0 ; set axis maxima

; Endstops
M574 X1 Y1 S0 ; set active low and disabled endstops
M574 Z1 S2 ; set endstops controlled by probe

; Z-Probe
M307 H3 A-1 C-1 D-1 ; disable heater on PWM channel for BLTouch
M558 P9 H5 F120 T6000 ; set Z probe type to bltouch and the dive height + speeds
G31 P25 X25 Y0 Z0.213 ; set Z probe trigger value, offset and trigger height
M557 X30:260 Y30:255 S30 ; define mesh grid

; Heaters
M305 P0 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 0
M143 H0 S110 ; set temperature limit for heater 0 to 110C
M305 P1 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 1
M143 H1 S280 ; set temperature limit for heater 1 to 280C

; Fans
M106 P0 S0 I0 F500 H-1 ; set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
M106 P1 S1 I0 F500 H1 T45 ; set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on

; Tools
M563 P0 S"Extr 1" D0 H1 F0 ; define tool 0
G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C

; Custom settings are not defined

; Miscellaneous
T0 ; select first tool

MJCT

I now realise that Z in the machine control dashboard, should be pointing 0.03 in the first case and 0.02 in the second, not 0.3 and 0.2

Still need your help

droftarts

@MJCT said in Nozzle gets smashed against the bed:

G31 P25 X25 Y0 Z0.213 ; set Z probe trigger value, offset and trigger height

You've gone from a probe trigger height of 3.2mm to 0.213mm, which seems very close. Did you follow the guide here to set the probe offset? https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#Section_Calibrate_the_Z_probe_trigger_height

Jog the nozzle down until it is just touching the bed or just gripping a sheet of paper. If the firmware doesn't let you jog it down far enough, send M564 S0 to disable axis limits.
Once you have the nozzle touching the bed, send command G92 Z0 to tell the firmware that the head is at Z=0
Jog the head up by 5 to 10mm
Send command G30 S-1 to report probe offset.

The first two points set the nozzle at Z=0. The second two determine the probe offset.

Ian

MJCT

@droftarts
0.213 was the value reported by G30 S-1 command twice in three attempts. Should I cut one decimal and impute 2.13 at G31?

And yes, I followed the wiki guide. I always do. The problem is that the guides usually don’t help me much. In this case the guide doesn’t provide any real example, neither it states the units in which the information is provided by the G30 or the units you must input at G31.

That’s why I am so thankful to this community. You have been fantastic. I´m not lazy, is just that WIKI guides suck big time.

fcwilt

Hi,

If the reported value was 0.213 that is what you use.

But that value is only valid if the Z position is correct, meaning Z=0 has the nozzle just touching the bed.

Frederick

MJCT

Tried “G31 P25 X25 Y0 Z2.13” instead of “G31 P25 X25 Y0 Z0.213” ... no surprises, it smashed the bed again!

MJCT

@fcwilt
Yes I understand that.

droftarts

@MJCT All units are millimetres. You can change to inches with G20, but this is supposed to be used only in gcode files, not for machine calibration.

Can you check that, after homing, if you send a command like G1 X100 Y100 Z0, the nozzle is not slamming into the bed? Or that the reported position of the nozzle is sensible. If that's the case, it's a problem with the gcode file. Check you haven't set any Z offset in Cura. Post you gcode file so we can check it.

Ian

fcwilt

@MJCT said in Nozzle gets smashed against the bed:

Tried “G31 P25 X25 Y0 Z2.13” instead of “G31 P25 X25 Y0 Z0.213” ... no surprises, it smashed the bed again!

Is the pin dropping when you issue a G30 command? The probe has to touch the bed and retract for the motion to be halted.

Frederick

MJCT

@droftarts Yes I understand that we are using SI units, supposedly mm, but I not sure of anything right now

@droftarts said in Nozzle gets smashed against the bed:

Can you check that, after homing, if you send a command like G1 X100 Y100 Z0, the nozzle is not slamming into the bed?

Funny (not really), yes it did slammed into the bed. But I did everything by the book (or not). Nozzle at the centre of the bed, just barely touching the bed (paper can still slide under), sent G92 Z0, pull bed down 15mm, sent G30 S-1, changed G31, sent M999.

The only thing I didn’t do is the "config-override.g " thing, because I just can’t find that file any ware

MJCT

@fcwilt

@fcwilt said in Nozzle gets smashed against the bed:

Is the pin dropping when you issue a G30 command? The probe has to touch the bed and retract for the motion to be halted.
Frederick

Yes, sent G30 command, the probe deplyed, bed moved up until it touched the probe than stoped.