G92 Z0 doesn't save Z position

[PixelGl1tch]

Board: Duet WiFi 1.02 or later
Firmware: RepRapFirmware for Duet 2 WiFi/Ethernet 2.04 (2019-11-01b1)
Duet WiFi Server Version: 1.23

Delta Printer - Rostock Max - SE300 Smart Effector

The title kinda says it all... I can home successfully, and everything seems to perform normally. I bring the hot end down and bust out the paper trick to get my Z0 position, then execute G92 Z0, then home all (homedelta). G0 Z0 then takes me back to the exact same position I was in before my G92 Z0, quite frustrating... Any ideas out there?

[fcwilt]

Hi,

Well without seeing any of your files I would guess that the homing the follows the G92 Z0 is resetting Z to the homed value.

It's been awhile since I had my deltas but as I recall I adjusted in the configuration the height parameter to get the nozzle touching the bed to be Z=0.

Or you could move the G92 to after the homing.

Frederick

[A Former User]

Home resets the G92 position.

You might need something like G92 Z0 G1 Z400 H3 to zero your Z, and then measure the axis height and store as M208?

[PixelGl1tch]

@fcwilt

Here is my homedelta file...

; homedelta.g
; called to home all towers on a delta printer
;
; generated by RepRapFirmware Configuration Tool v2.1.2 on Wed Nov 20 2019 23:41:27 GMT-0600 (Central Standard Time)
G91 ; relative positioning

G1 H1 X478 Y478 Z478 F1800 ; move all towers to the high end stopping at the endstops (first pass)
G1 H2 X-15 Y-15 Z-15 F1800 ; go down a few mm
G1 H1 X10 Y10 Z10 F360 ; move all towers up once more (second pass)
G1 H2 X-15 Y-15 Z-15 F6000 ; move down a few mm so that the nozzle can be centred
G90 ; absolute positioning
G1 X0 Y0 F6000 ; move X+Y to the centre

[Phaedrux]

This is your guide to delta success: https://duet3d.dozuki.com/Wiki/Calibrating_a_delta_printer

G92 Z0 sets the current position to Z0, but that only holds true until the printer is homed again. When you home the XYZ towers, the position is going to be reset to the M208 maxima values. If everything is calibrated correctly, this shouldn't matter and you should still be able to return to Z0, but as you've found, you have a discrepancy, which means your homed height is off.

How are you calibrating?

[PixelGl1tch]

Thanks for the response, super helpful. So as I understand it now, M92 Z0 is really just for the purposes of finding a specific location relative to the one that you are at when you execute the command, not for actually storing anything for future use - please correct me if incorrect.

I have since updated the home height to the correct position based on the change required to Z after my M92 Z0 to reach my desired Z0 location, and b00m, back in business! Appreciate your responses, and this amazing community.

[droftarts]

@PixelGl1tch:
G92 sets position of where the nozzle is at the current time, it doesn't move to/'find' a location, that would be G1.

Note M92 sets the steps per mm! Make sure you type this in right.

Ian

[PixelGl1tch]

@droftarts

Ahh, good callout, fortunately just a typo on my part here and not anywhere else so far...