When I finish a print a large retraction seems to occur - clogging

[gzcwnk]

Hi,

When the print finishes it seems that a substantial retraction occurs (like 50mm+). It is so bad that the filament goes up past the extruder's gear and I have to reload the filament by hand every time. This is annoying, but worse the swissmicro hotend now has molten filament in its cold end and hence it often cloggs solid. This means I have to heat the hotend to get the nozzle off and dismantle the extruder assembly in order to poke the cold plug out from the top.

So I am pretty desperate to stop this retraction, 1~2mm yes, not what must be 50mm or something. I assume its a setting in the duetwifi? as the same gcode in the wanhao mainboard didnt cause this.

[Qdeathstar]

I don't think that getting molten plastic in the cold end from retraction causes jams, after all you can retract manually to unload filament….. it's more likely that molten filament is getting into the cold in during the print and then clogging after the print is finished..

[dc42]

The usual cause of a large retraction is that you configured your slicer to use absolute extrusion coordinates (we recommend relative), and in your end gcode or your stop.g file you forgot to switch to relative mode (M83) before your G1 command to retract a little filament.

[gzcwnk]

@Qdeathstar:

I don't think that getting molten plastic in the cold end from retraction causes jams, after all you can retract manually to unload filament….. it's more likely that molten filament is getting into the cold in during the print and then clogging after the print is finished..

I am going to say no, I dont think so. Every time I go to print I find the filament can no longer be extruded as its been ejected. The filament has simply strung out and got very thin so what's left separates easily when I pull. So its more like a large retraction has pulled molten filament up into the cold end at the end of the print. The std setting I have for retraction is microswiss's, 1mm and I ran that for 3 months with Wanhao's board before it failed with no issues. So I suspect its something else.

[gzcwnk]

@dc42:

The usual cause of a large retraction is that you configured your slicer to use absolute extrusion coordinates (we recommend relative), and in your end gcode or your stop.g file you forgot to switch to relative mode (M83) before your G1 command to retract a little filament.

Thanks, being new to this its knowing where to start looking. I have not edited the stop.g file, I will go look/check. I have not changed Wanhao's cura's settings much so I will try and find something to show you.

[gzcwnk]

Hi,

Cura has end code, here it is.

So the "bad" lines are,

"G1 E-1 F300
G1 Z+0.5 E-5 X-20 Y-20"

If that is -5mm that is not good for the swissmicro I suspect but doesnt explain it unless its the absolute/relative thing you mentioned..

So I can change it to,

"G1 E-1 F300
G1 Z+0.5 E-1 X-20 Y-20"

so that gives me 2mm retraction?

where does the M83 go? before both?

So,

"M83
G1 E-1 F300
G1 Z+0.5 E-1 X-20 Y-20"

?

original file,

;End GCode
M104 S0 ;extruder heater off
M140 S0 ;heated bed heater off (if you have it)
G91 ;relative positioning
G1 E-1 F300 ;retract the filament a bit before lifting the nozzle, to release some of the pressure
G1 Z+0.5 E-5 X-20 Y-20 F{travel_speed} ;move Z up a bit and retract filament even more
G28 X0 Y0
G90
G1 Z170 ;move X/Y to min endstops, so the head is out of the way
M84 ;steppers off
G90 ;absolute positioning
;{profile_string}

[dc42]

Yes put M83 after the G91. Looks like Cura expects G91 to set the extruder to relative as well as the axes, but in RRF G92 sets only the axis to relative and you need M83 to set the extruder to relative.

[gzcwnk]

Thanks will try this evening, but it will be a 31 hour print before I know!