RE: Color change, dot outside printing area?
To be clear, the issue being discussed does not occur on MK3 printers.
Happens on MK2 and MK3
Regards joan
RE: Color change, dot outside printing area?
As I suspected, Prusa support is focusing on the oozing just before the burp. I don't know how to explain it to them more clearly that it's not an oozing issue. We can clearly see the bubble purge just as the nozzle is hitting the print.
RE: Color change, dot outside printing area?
As mentioned previously this happens to me every time on both a Mk3 and a Mk4, the difference is that the Mk4 seems to deposit more filament at the touchdown point. The Mk3 does still leave some filament but it's definitely a lot less than the Mk4.
The way I have got around it is to set the printer up as a multiextruder printer but enable the single extruder checkbox. I also used the extruder values that were posted by ChrisHill in the other thread https://forum.prusa3d.com/forum/english-forum-original-prusa-i3-mk4-general-discussion-announcements-and-releases/still-having-issue-when-manually-changing-filament-during-a-print/#post-671334 .
By enabling the wipe tower with the multiextruder settings this places the blob away from the model and the issue is gone. It also allows you to do multicolor single layer prints rather than having each color on a different layer.
If you don't want to set up the multiextruders then, in Prusaslicer add a small shape that's at least as tall as your highest color change. As long as this prints after the main object then the blob will be placed on this sacrificial object and all should be good.
These are of course workarounds and I'd love to see it fixed in some way by Prusa.
RE: Color change, dot outside printing area?
I agree with your post in that there can be something similar on an MK3 but I have never has an occurrence where on the MK3 it left such a "dot" welded to the print that could not be removed. In my cases the little speck left behind on the MK3, if it is even left behind at all, can easily be removed by scraping with my fingernail.
I have started reworking all of my models to use single-extruder MMU but what a pain it is to have to create this workaround for an obvious issue. I too would like to see this addressed...at least acknowledged and investigated! We're so used to having to find workarounds for issues. I don't know how to get Prusa to listen. Maybe I'll try submitting an issue on Github.
RE: Color change, dot outside printing area?
Github definitely seems the right place for reporting bugs or suggesting new things.
RE: Color change, dot outside printing area?
Have you tried PrusaSlicer 2.7.2? The way M600 functions has been changed to alleviate this issue. It's still not perfect but it does help.