IDEX - How to Set Z Offsets?

RogerPodacter

@RogerPodacter to clarify, basically it appears that my G10 offset values are completely ignored for the U carriage right 2nd Toolhead. whether i set positive Z , negative Z, small or large value, it is always ignored and the U carriage is 0.5mm higher than the X carriage. i tried searching the forum but all similar posts dont seem to actually help make a difference when i attempt solutions.

droftarts

@RogerPodacter this sounds like the same issue as in this thread https://forum.duet3d.com/topic/32245/idex-right-head-z-adjustment-using-g10
By measuring off the shorter tool, you’re trying to go below Z0 with the second longer tool. I’ll check with @dc42 if there’s any other reason Z offsets are not being applied.

Ian

RogerPodacter

@droftarts ok yes this is exactly what is going on, and after reading so many threads on this topic, i think i finally understand. it appears for toolchangers or IDEX machines, there is a limitation of which Head Reference Point HRP point you chose, and you should always select the "shortest" tool as your zero point. Unless i am misunderstanding, but this could be added to the documentation and would make an enormous improvement for the offset parameters. or at least add it as a footnote? apologies if its already stated and i just missed it.

EDIT: i am attempting these different methods:

set my Euclid Klicky probe G31 X0 Y0 Z0 as the HRP, then set T0 and T1 offsets accordingly.
G31 X0 Y0 Z0
G10 P0 X28 Y20 Z-9.21
G10 P1 X28 Y20 Z-8.81
Set my Z probe with its true offsets:
G31 X-28 Y-20 Z9.21
G10 P0 X0 Y0 Z-0.4
G10 P1 X0 Y0 Z0
Compensate my true Z offset by 1mm to encompass both nozzle heights
G31 X-28 Y-20 Z8.21
G10 P0 X0 Y0 Z-1.40
G10 P1 X0 Y0 Z-1.00

none of these cases seem to work correctly for me, and i'm always stuck with the 2nd carriage Z offset being "ignored" in the negative direction. the shorter nozzle just can never go low enough to the bed.

droftarts

@RogerPodacter That's odd, I would expect the second one of those to work. What firmware version are you running, on what hardware? Or just M115 output.

Ian

RogerPodacter

@droftarts i just modified my post to add a 3rd condition i attempted, but it still didnt work. what is happening is that once the software registers the Z trigger during probing, in all cases it simply ignores any offset going below that physical actual probe point it registered. so even if i select my HRP as the shortest nozzle, it is still ignored and restricted from going in the negative direction as an offset.

the only method i havent yet tried is making the U axis have a -0.44mm offset using the M208 command. but this feels so wrong to me for some reason.

here are my outputs:

5/12/2023, 7:52:49 AM 	M115
FIRMWARE_NAME: RepRapFirmware for Duet 3 Mini 5+ FIRMWARE_VERSION: 3.4.2 ELECTRONICS: Duet 3 Mini5plus WiFi FIRMWARE_DATE: 2022-09-13 15:14:33

I have 2 toolboards 1LC and an expansion board 3HC but i dont think those have any impact on this issue.

dc42

@RogerPodacter said in IDEX - How to Set Z Offsets?:

set my Euclid Klicky probe G31 X0 Y0 Z0 as the HRP, then set T0 and T1 offsets accordingly.
G31 X0 Y0 Z0
G10 P0 X28 Y20 Z-9.21
G10 P1 X28 Y20 Z-8.81

If the Z offsets are negative, that means the nozzles are lower than the klicky probe. Is that right? If so, how do you probe without the nozzles hitting the bed before the probe?

dc42

PS - a possible source of confusion is that for historical reasons the G31 Z parameter is the trigger height of the probe, i.e the height of the HRP when the probe triggers. This means that the G31 Z parameter is in effect the negative of the Z offset of the probe; whereas the G31 X and Y parameters are positive offsets.

RogerPodacter

@dc42
UPDATED
i actually already tried both positive and negative versions of those offsets with no success. so i dunno what to think anymore.

EDIT: to confirm, after trying both positive and negative numbers, the behior remains unchanged. what is happening is that phyiscally the shorter toolhead 2 simply will not go lower, and any offset applied from G10 either positive or negative, it simply zeros the Z height displayed in DWC to be that tool's offset value, but physically the nozzle never can go lower and reach the bed. unless i'm doing something wrong.

RogerPodacter

@RogerPodacter i ultimately fixed my issue by using method 3. The G31 must be manually compensated to artificially add height to the Z offset. Since i have the Z probe on the left carriage, but the right carriage is the shortest, i had to artifically add that difference to the G31 command.

G31 Z9.21 plus 0.5mm = G31 Z9.71

Once this is done, now i get success with the following:

Compensate my true Z offset by 0.5mm to encompass both nozzle heights
G31 X-28 Y-20 Z8.71
G10 P0 X0 Y0 Z-0.40
G10 P1 X0 Y0 Z0.00

I think updating the documentation with a footnote of some type might greatly help people with Z offset issues.

Another way to think of this is the HRP should always be set to the shortest toolhead nozzle, even if the Z probe is on a different toolhead, because the firmware limits negative direction offsets, even if you set it in the G10 command.

Also one risk with this method is that when manually moving the left carriage you have the ability to run the nozzle into the bed by 0.4mm (or whatever your difference height is for your setup). so just need to be mindful of this.

droftarts

@RogerPodacter thanks for replying with your working setup. I was going to try and test this on Monday. I’ll add a section on Z offsets to the documentation

Ian