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

dc42 · 3 Feb 2018, 21:46

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 · 3 Feb 2018, 22:42

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 · 3 Feb 2018, 23:00

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 · 4 Feb 2018, 07:35

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 · 4 Feb 2018, 14:12

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 · 11 Feb 2018, 22:29

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 · 12 Feb 2018, 06:33

@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 · 12 Feb 2018, 08:01

@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 · 12 Feb 2018, 16:47

@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 · 12 Feb 2018, 18:28

@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.