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How to stop oozing after colour change  

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ohmygosh
(@ohmygosh)
Member
How to stop oozing after colour change

I’m starting to do more prints with colour changes using a single nozzle using the Prusa slicers automatic colour change setting which I think is the M600 command in the G Code. 

But the consistent issue is that after the filament change is done, the nozzle oozes filament as it slowly makes its way back to the print and ruins the first layer of the new colour. 

I’ve tried getting AI to write some different code options to get it to go back and do a fresh purge line, like at the start of a new print but I can’t get it to work. Partly because I think the M600 command is and end-to-end firmware instruction so it always does this slow move back to the build plate. 

Has anyone got a good solution to this?

Many thanks

Posted : 07/09/2025 1:37 pm
hyiger
(@hyiger)
Estimable Member
RE:

I have the exact same problem. I contacted support over chat and their response: "We are not allowed to discuss g-code modifications" So I started looking into this. I've done exactly 2 multicolor prints so it's not a big priority for me. However, I ran into the same issue, M600 is a Marlin g-code filament change macro. My thinking is find out what composes it and try to break it down into individual g-code then add in: G1 E0.3 F1500 ; prime after color change

This post was modified 1 day ago 3 times by hyiger
Posted : 07/09/2025 4:13 pm
hyiger
(@hyiger)
Estimable Member
RE: How to stop oozing after colour change

OK, this is interesting. I think in Color Change G-code section change M600 to M600 E0.3 (assuming this is supported).

I'll try it later and see or maybe even pull the firmware source from github and hunt it down.

M600 - Filament Change 1.1.0  filament  Automatically change filament ADVANCED_PAUSE_FEATURERelated codes: M603 M701 M702Description

The M600 command initiates the filament change procedure. The basic procedure will move the print head away from the print, eject the filament, wait for new filament to be inserted and the user to confirm, load and prime the filament, and continue with the print. M600 may be initiated automatically if a filament runout sensor is installed.

Notes

Requires ADVANCED_PAUSE_FEATURE.

The settings for this command can be found in Configuration_adv.h. At this time M600 requires an LCD controller.

UsageM600 [B<beeps>] [E<pos>] [L<pos>] [R<temp>] [T<index>] [U<pos>] [X<pos>] [Y<pos>] [Z<pos>]Parameters[B<beeps>]

Number of beeps to alert user of filament change (default FILAMENT_CHANGE_ALERT_BEEPS)

[E<pos>]

Retract before moving to change position (negative, default PAUSE_PARK_RETRACT_LENGTH)

[L<pos>]

Load length, longer for bowden (positive)

[R<temp>]

Resume temperature. (AUTOTEMP: the min auto-temperature.)

[T<index>]

Target extruder

[U<pos>]

Amount of retraction for unload (negative)

[X<pos>]

X position for filament change

[Y<pos>]

Y position for filament change

[Z<pos>]

Z relative lift for filament change position

Posted : 07/09/2025 4:26 pm
Diem
 Diem
(@diem)
Illustrious Member

This is the extruder repressurising the nozzle, if you remove this step you will get underextruded spots at each change.

One option is to use a purge tower; another is to use @joantabb's method from MK3 days, it might be slightly harder with a core one but the principle remains sound:  When the change completes and the nozzle extrudes the new filament and asks whether the colour is correct - DON'T remove the dribble, instead hold the dribble, click YES and the new dribble adds to the stuff in hand until, as the toolhead moves back to the work it breaks off the dribble and arrives clean.

Cheerio,

Posted : 07/09/2025 10:44 pm
2 people liked
hyiger
(@hyiger)
Estimable Member
RE: How to stop oozing after colour change

Or wait for the INDX tool changer...

Posted : 07/09/2025 11:11 pm
ohmygosh
(@ohmygosh)
Member
Topic starter answered:
RE: How to stop oozing after colour change

Thanks folks. 

I managed to get a good result by adding a manual purge tower and holding the filament until the last moment. A bit fiddly but for these intricate models I’m making it solves the problem for now. 

Appreciate the helpful input.  

Posted : 07/09/2025 11:34 pm
1 people liked
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