Conditional homing and z-height fine adjustment

[fcwilt]

@GuidoP said in Conditional homing and z-height fine adjustment:

I have had several considerations for implementing the z-max switches: ...

Thank you for the reply.

All of my printers home to Z min and it seems to me all of the reasons you stated for using Z max apply to Z min.

• The crash scenario is the same for min versus max.

• Most slicers will execute some user defined code on print completion. One of the things my "printing complete" macro does is move down to a bit - it could just as easily move to Z max.

• I don't understand the fixed reference issue. You are referencing the frame when using either min or max - correct?

Thanks for the help in understanding.

I don't know if this makes any difference but I eliminated multiple Z steppers in favor a single stepper, belt driven setup which naturally keeps both Z axis lead screws in sync.

Frederick

[GuidoP]

@fcwilt Thanks for sharing your thoughts and considerations.
An alternative to my current setup would indeed be using a z-min homing scenario and just use the endstops as safetystops so the bed wont crash when is full down when the machine starts. (This is actuatlly my backuo scenario if i don't get the macro running).

The crash scenarion in a z-min homing situation is higher imho:

• Machine starts, axis are not homed. The machine has no clue where the different axis are located
• Homing is initiated. X and Y homing will initiate (in the default g-code) a Z move in the z-max direction. Regardless if z-max or z-min is used
• If the bed is at or near the z-max position, with z-min endstops the machine has no way of knowing it will run out of bed travel and will crash to the mechanical limits. In a z-max endstop configuration the z-max endstop will trigger, stopping the move gracefully. With to independend z-motors you'll need to re-perform the bed leveling again due to the unknown shift between the two leadscrews. I'm not sure what would happen in your setup with a single stepper for 2 leadscrews. Does the belt slip or does the stepper skip steps?

I have two optical endstops bolted to the frame between steppermotor and linear rod. As the frame is square and level these switches are in the same position horizontally. I use a single 25mm aluminium angle profile bolted directly to the 2020 profiles of the bed as endstop flag. So basically there are no manual adjustments and everything is referenced to a fixed point resulting in a repeatable fixed horizontal level.
An alternative to this procedure on the z-min side would be using the z-probe to probe near the leadscrews and let the duet calculate how to level things out. This is a bit more straight forward without extra probing time. (Or use a single steppermotor which drives 2 leadscrews.... )

There are a lot of differnt approaches and sollutions to solving a single problem. These are my solutions now, which i might (or might not) change in the future... That's the beauty of learning and progressing...

Anyway, i'm getting a bit off-topic... Sorry...

[fcwilt]

@GuidoP said in Conditional homing and z-height fine adjustment:

• Homing is initiated. X and Y homing will initiate (in the default g-code) a Z move in the z-max direction. Regardless if z-max or z-min is used

If it moves in the Z max direction when using Z min end stop then something is wrong. It should not do that.

Frederick

[Phaedrux]

@fcwilt said in Conditional homing and z-height fine adjustment:

If it moves in the Z max direction when using Z min end stop then something is wrong. It should not do that.

Maybe he means the small lift before homing x and y for clearance?

[fcwilt]

@Phaedrux said in Conditional homing and z-height fine adjustment:

Maybe he means the small lift before homing x and y for clearance?

What small lift? I must do things backwards. I home Z first and then move to Z=5 before I home Y & X.

Frederick

[Phaedrux]

@fcwilt For instance in homeall.

G1 Z5 F100 S2 ; Lower bed 5mm to ensure it is below the trigger height

[fcwilt]

@Phaedrux said in Conditional homing and z-height fine adjustment:

@fcwilt For instance in homeall.

G1 Z5 F100 S2 ; Lower bed 5mm to ensure it is below the trigger height

What would you do that?

Consider when homing to Z min:

G1 Z-999 H1
G1 Z20
G1 Z-999 H1

When the first G1 executes if the endstop is already triggered no movement takes place and the next G1 executes which is safe.

Am I overlooking something?

Frederick

[Phaedrux]

@fcwilt said in Conditional homing and z-height fine adjustment:

Am I overlooking something?

Yes, when using a probe you must position the probe first, so X and Y must be homed first, and by default the configurator includes a short lift of the Z axis to give clearance for the X Y move and to lift the probe above trigger height.

But I was just speculating on what he might have been meaning.

[fcwilt]

@Phaedrux said in Conditional homing and z-height fine adjustment:

Yes, when using a probe you must position the probe first, so X and Y must be homed first, and by default the configurator includes a short lift of the Z axis to give clearance for the X Y move and to lift the probe above trigger height.

Ah... I see.

I use a Z min endstop switch setup for homing in relation to the frame so I never encountered that issue.

I only use the Z probe for setting Z=0 and mesh comp probing, things which only occur after the ZYX homing has been done.

Thanks.

Frederick

[GuidoP]

@Phaedrux said in Conditional homing and z-height fine adjustment:

@fcwilt said in Conditional homing and z-height fine adjustment:

If it moves in the Z max direction when using Z min end stop then something is wrong. It should not do that.

Maybe he means the small lift before homing x and y for clearance?

Thats correct

[GuidoP]

Thanks all for the input, but unfortunately it does not bring me closer to an answer to the original question: Why does the conditional gcode not work as intended? Where is the bug in the code??

[GuidoP]

I finally got the macro working with following code:

; Source: https://forum.duet3d.com/topic/4202/homing-to-z-max-when-also-using-a-z-probe/19
; Start g-code: G28, M98 P"0:/macros/Leveling/SetZ" ; run z fine tuning
 
; If the printer hasn't been homed, home it
 
;M291 P"checking homing status" R"Homing status" S1			; Report status
 
if !move.axes[0].homed || !move.axes[1].homed || !move.axes[2].homed  	; Check if axis are not homed
  ;If axis are not homed, home axis
  echo "Axis are not homed, performing homing"
  M98 P"0:/sys/homeall.g"
else
  ;If axis are already homed, home only the X and Y axis
  echo "axis are homed, re-homing x and Y"
  M98 P"0:/sys/homex.g"											; Run the Home X macro
  M98 P"0:/sys/homey.g"											; Run the Home Y macro
  ;G1 X100 Y100 H0 F1800											; move to be centre slowly.
  
;End homeing check
M291 P"Axis homed" R"Homing status" S1							; Report status
;echo "start fine tuning z-level"
G1 X100 Y100 H0 F1000											; move to be centre slowly.
G1 Z15 H1 F8000	 	 											; Raise the bed to start probing
G30 															; probe for z=0
G1 Z10 H1 F1000 												; raise nozzle
G30 S-1 														; check z gap
G1 Z10 H1 F1000 												; raise nozzle
 
M400															; Wait until all moves are completed

I changed and tested several different thing, but i think the trick that did it was removing the empty line between the end of the "If" block and the start of the "else" block.