Got everything working, in the end I just ditched the line M564 H0
and everything else stayed as it was - and it's printing!

Thanks.

I'm reading this thread and I have flashbacks - I started the same way, as you didi767, with an Ender3 and a Duet.
The first tihing I did after getting Duet up and running, I added second Z motor and lead screw, to get rid of Ender's sagging X-gantry issues.
After all my modifications, my Ender looked more or less like a some sort of Franken-Prusa, basically the frame was from Creality, gantry was
a Prusa X gantry and I had Ender3 bed. In the end I decided to build a closed COREXY and I have a Duet3, the
Creality frame is not meant for heavy-duty printing I think. The wheels need adjusting and the frame is too narrow.

Got everything working, in the end I just ditched the line M564 H0
and everything else stayed as it was - and it's printing!

Thanks.

@Phaedrux said in Modified Ender-3 behaves strangely when starting to print:

Where are you sending G92 Z0? I don't see that anywhere in your homing files.

When calibrating the Z height, I'm sending the command G92 Z0 to tell the firmware that the head is at Z=0,
it's not in the homing files.

I try to get access to the printer and go through the code once more.

@Veti said in Modified Ender-3 behaves strangely when starting to print:

@Tanel_76

so when you enter G28

and move to G0 Z0 then nozzle is above the bed?

No, and that's the strange thing. after resetting Z
I go G1 Z100 F400 and come down to G1 Z5 F400
the nozzle ploughs into the bed. When I move
down step by step, I see that the nozzle is above the
bed around Z55 which is not logical at all.

It's as if the G92 Z0 value is not entered correctly
and the Duet gets another value from somewhere,
which I can't find.

PS Im using this guide
https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe#:~:text=In Duet Web Control%2C go,Save the file.

And Duet seems to have the same symptoms, as if when you forget the M500 command after resetting Z in Marlin.
I have to go to config-override.g and check that there are no G31 commands, when I'm near the printer again.

@CaLviNx said in Modified Ender-3 behaves strangely when starting to print:

I have an operational config.g if you want a copy

Is it possible to see the conf.g that you are using?

The last conf file is here:
https://pastebin.com/npPJ2iSK

It's basically the same conf.g that I had uploaded earlier,
I just changed the M671 and also thermistor settings.

I copied the CaLviNx bed.g that he generously posted here.

When I start a print job, the nozzle goes down about 4.5mm,
I also recalibrated the Z height about 5 times,
the drop in Z height was constant every time.

Homeall
homez.g

I think these are pretty standard.

Hi,

I threw the start.g out, after that the anomalies disappeared.

The only issue is now the Z height, I have calibrated and reset the (G92 Z0)
got the trigger height 2.4 and I have it in mu config.g
Still, when starting to print, the nozzle goes like 4.5mm downwards
from the calibrated height.

I deleted the slicer start code (the initial line in Cura)
just to see, what's happening.

Got the machine calibrated,
it's homing fine, when starting to print, it homes all,
then starts immediately move upwards, until Z145
then waits and starts to come back towards the bed slowly.

Strange.

@Tanel_76 said in Modified Ender-3 behaves strangely when starting to print:

G28 ; home
G30 P0 X20 Y100 Z-99999 ; probe near a leadscrew, half way along Y axis
G30 P1 X180 Y100 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors

Hi,
I would like to see it, if possible.
I got the machine to properly do the x-gantry calibration, now
next thing to do is to the mesh compensation, after that I will try
to print the test cube again.