Mysterious retraction:

[schmluka]

Hi,

I have a tool changer running a prime.g script after picking up a tool.
Prime.g is supposed to brush over the nozzle, purge the nozzle with filament, brush again and start printing.
What I find is happening, that after the purge I'd like to have 3mm retraction, but I get approx. 10mm (10second long, not sure how much). Does anyone see where it comes from?

purge.g:

;brush in
G1 X-23 Y171 F25000
G1 X-23 Y207 F25000
G1 X-23 Y171 F25000
G1 X-23 Y207 F25000
 
;Park for prime/purge
G1 X-23 Y223 F50000
 
;Prime
G92 E0
G1 E50 F200 ;extrude 50mm
 
; HERE: approx. 10s of slow retraction. Why?
 
G1 E-3 F200 ;retract 3mm
G92 E0
 
;Run Out
G1 X-23 Y207 F50000
 
;Brush Out
G1 X-23 Y205 F25000
G1 X-21 Y200 F25000
G1 X-23 Y195 F25000
G1 X-21 Y190 F25000
G1 X-23 Y185 F25000
G1 X-21 Y180 F25000
G1 X-23 Y175 F25000
G1 X-21 Y170 F25000
 
G1 X-23 Y170 F25000
G1 X-23 Y205 F25000
;brush in
G1 X-23 Y171 F25000
G1 X-23 Y207 F25000
G1 X-23 Y171 F25000
G1 X-23 Y207 F25000

[fcwilt]

Hi,

Is the extruder set to Absolute or Relative mode?

Frederick

[schmluka]

Using PrusaSlicer, "use relative E distances" is unchecked. So I guess absolute?

[fcwilt]

@schmluka said in Mysterious retraction::

Using PrusaSlicer, "use relative E distances" is unchecked. So I guess absolute?

Check it and try again.

Frederick

[schmluka]

is there any other work-around? I always thought you are supposed to use absolute extrusion values for higher precision?

[fcwilt]

@schmluka said in Mysterious retraction::

is there any other work-around? I always thought you are supposed to use absolute extrusion values for higher precision?

I was always told to use relative.

---

Link to article talking about Relative or Absolute

---

With relative you retract with negative values - G1 E-3.

But with absolute to retract 3mm after a G1 E50 you would use a G1 E47.

Frederick

[Phaedrux]

@schmluka said in Mysterious retraction::

is there any other work-around? I always thought you are supposed to use absolute extrusion values for higher precision?

The firmware has to convert to relative extruder values anyway. Absolute is a holdover from the early days of reprap and can be safely left behind.

[schmluka]

@fcwilt Thanks for the quick help. Changing to relative E distance worked.