Cartesian - Z-endstop & homing (Max or Min)?

RGN01

I thought I'd add my bed.g file and explain another weird symptom. When homing Z, it is setting Z0 about 2mm above the print surface. My workflow to that point is (all using the IR Z-probe to home and probe and using the config.g above and bed.g below):

disable be compensation and mesh compensation using DWC controls
home all axes - after homing, head height displays as 2.00mm but is much more visually
drop Z to Z=0 DWC head height - it is still about 3mm above the surface
in effort to get it to a 'proper' Z=0, I run G92 Z10 - this to set an artificial position to allow the head to go lower
carefully lower head 2.3mm using DWC axes movement buttons until it just grips a sheet of paper.
run G92 Z0.2 to set the actual head height to 0.2mm to compensate for the paper thickness
raise the head 10mm
home all axes
head height is once again displaying as 2.0mm but is much higher

; bed.g
; called to perform automatic bed compensation via G32
;
M561 ; clear any bed transform
G28  ; home all axes
; Probe the bed at 5 points
G30 P0 X10 Y20 H0 Z-99999 
G30 P1 X10 Y230 H0 Z-99999
G30 P2 X210 Y230 H0 Z-99999
G30 P3 X210 Y20 H0 Z-99999
G30 P4 X110 Y120 H0 Z-99999 S

I must be misunderstanding the logic and missing something here but I can't see what I'm doing wrong so any pointers gratefully received.

Richard

Dougal1957

Try jogging the nozzle down to paper hight send G92 Z0 raise the nozzle say 5mm send G30 S-1 and read of the resultant Z Hight in the DWC.

Then adjust the Z Offset param in the G31 line of your Config.g to match

RGN01

Thanks, Doug, I've done that - it is how I got to the offset in the G31 P500 X9 Y21 Z2.43 line of config.g I did it a few times to check, too, and it was consistent and is about as designed on my own-design carriage (designed height was 2.5mm).

I've also removed the heightmap.csv file (well, renamed it) in case it was causing issues somehow. No change.

Richard

Dougal1957

um strange one

RGN01

Yeah, it has me stumped!

Richard

RGN01

Not sure if I mentioned, so adding the firmware version:

Firmware Name:	        RepRapFirmware for Duet WiFi
Firmware Electronics:	Duet WiFi 1.0
Firmware Version:	1.20 (2017-12-23)
WiFi Server Version:	1.20
Web Interface Version:	1.20

Richard

dc42

After you do Z homing, are you certain that if you command the printer to Z=0 the nozzle is just touching the bed? A very small number of users have reported that their IR sensors sometimes have a secondary trigger height some distance above the proper one. In such cases we have replaced the sensor.

RGN01

Thanks, David. It is perhaps easiest if I explain what I'm doing. I ran my homez.g:

;Z-Probe endstop
G1 X110 Y110
G91			; relative positioning
G1 S1 Z-250 F9000	; move quickly to Z axis endstop and stop there (first pass)
G1 Z5 F6000       	; go back a few mm
G1 S1 Z-250 F360  	; move slowly to Z axis endstop once more (second pass)
G1 Z2 F4000      	; raise Z again
G90               	; absolute positioning

After running that, the nozzle stopped about 4.5mm from the bed but the Z-height displayed on DWC was 2.0mm. Issuing G1 Z0 dropped the nozzle to about 2.4mm above the bed but DWC height shows 0mm.

The measured heights were measured using a stack of Post-It notes and a vernier so there is a reasonably large margin of error!

I tried this with bed compensation enabled and disabled and it made no noticeable difference.

Running bed compensation immediately after this returns "Mean error: -2.591 mm" but the bed is very close to level.

Was the false detect of those IR probes about 2 to 2.5mm greater than the main trigger distance?

Richard

RGN01

OK, I think I have found the issue - somehow my homeall.g, did not have G30 in it. Not at all sure how I lost it but added it back and it seems to be working correctly.

I'm sorry for the confusion - I've been battling this for days and somehow overlooked that missing G30!

Richard

dc42

I'm glad you solved it. Your homez.g file should also be using G30, not G1 S2 Z moves. See https://duet3d.com/wiki/Configuring_RepRapFirmware_for_a_Cartesian_printer#Homing_Z.

RGN01

Thanks, David. I've now reverted to the Z-max endstop and am using the probe for probing prior to a print. I will write up my settings etc. in a new thread as it may help someone else get this combination working (e3d Chimera, IR probe and Z-max endstop).

I really do appreciate you help - thank you!

Richard

SputnikOC3d

Interested in the settings needed to get Z max endstop with Z min [ probe ] workign correctly. my current config doesnt actually stop the Z+ movement when the endstop is triggered

RGN01

@SputnikOC3d:

Interested in the settings needed to get Z max endstop with Z min [ probe ] workign correctly. my current config doesnt actually stop the Z+ movement when the endstop is triggered

Details of my printer and the config files are here https://www.duet3d.com/forum/thread.php?id=4306

Hope this helps.

Richard

SputnikOC3d

@RGN01:

@SputnikOC3d:

Interested in the settings needed to get Z max endstop with Z min [ probe ] workign correctly. my current config doesnt actually stop the Z+ movement when the endstop is triggered

Details of my printer and the config files are here https://www.duet3d.com/forum/thread.php?id=4306

Hope this helps.

Richard

Thanks Richard … Im looking at this ..

; Endstops Z-probe
M574 X1 Y2 S1 ; Set active high [ NC ] endstops
M574 Z2 S0 ; set active low [ NO ] endstops
M558 P1 H6 F300 T8000 ; Set Z probe type to unmodulated and the dive height + speeds
G31 P500 X9 Y21 Z2.2 ; Set Z probe trigger value, offset and trigger height
M557 X10:220 Y25:220 S20 ; Define mesh grid

Is it possible I need a NO normally OPEN type switch for this to work when using a probe on this axis? Mine is currently NC. I cant understand why that would be … but - ya never know ...

Also may I ask another probably dumb question ... How did you determine the X/Y offsets off the probe on your G31 code? My BL touch mounts into a Prusa MK2 extruder assmbly.... and I dont think the thingiverse creator of the add on probe mount took any time to CAD that data out ... and Im not sure how to accurately measure these offset ... Is there a tutorial or a guide somewhere _ive looked - no find ...

PS - I noted your max speeds and current settings are far greater than mine ... NEMA 17s on this printer? My Z is kinda noisy and my speeds arent all that exciting. Was hoping to get quieter and faster ... think I need 24v vs. my 12v PSU ... and to uptick the power and speeds ...

Thanks for any help you could share here

All the best,

Steve

Stoop

@dc42:

Yes, except:

1. You probably want something more like G1 X100 Y100 Z5 so that bed probing starts from 5mm height.

2. You should not use G92 to set the Z height after the G30. Use the G31 Z parameter instead.

So, I'm VERY new to 3d printing.
WHY don't you wanna use G92 after G30?

dc42

@Stoop:

WHY don't you wanna use G92 after G30?

The firmware needs to know the Z probe trigger height anyway for other bed probing purposes. There is no point in putting the same information in two different places, you will just confuse yourself if/when that value changes.