I have two objects on my printbed. After about 30 out of 500 layers I skipped one of them as I just needed the rough outline to test fitting but wanted to complete the main object. Basically a single coaster and a storage box for coasters.
Now both are multi-coloured … as I say at layer 30 I skipped and only the smaller object, the coaster, has colour on (which is skipped) and the large case should only have colour some 400 layers later.
Despite the fact it does indeed skip printing the smaller object, it still performs filament changes, purges and prime tower layers using the colour it doesn’t need anymore.
For example :
The smaller with yellow in the front is skipped. The larger purple in the back has still about 8hrs and 450 layers to go and the only yellow colour on the large item is some writing - so I’d expect maybe only the three top layers need a color change.
So once a layer of purple on the large one is printed, it changes to yellow, purges it, prints on the prime tower and goes straight to cut the filament to change back to purple.
This seems unnecessary waste of filament and time.
Here you can see it changed into yellow just to prime the nozzle to then go back cutting
From 1.7.4 release notes:
1. Support skipping objects in multi-filament(multi-color) printing
Currently, the function is not in its optimal state. Changing the filament and flushing cannot be skipped, even if the filament becomes useless after skipping objects. If we skip filament changes and flushing when the filament is deemed useless, the filament ordering would change as well. This could lead to disorganized flush volume and cause color mixing in the models. Despite these challenges, users can still benefit significantly by only excluding failed objects in multi-filament printing. We will continue to improve and plan to support skipping flushing and changing filaments in the future.
I think the main problem relates to the prime tower structure and purging volumes which would add quite a lot of complication to the dynamic adjustments that the printer would need to make if one or more colours are removed from the print.
Not impossible to solve - probably with some pre-built dummy GCODE that only gets invoked if specific objects (or combinations) are removed at print time.
I suppose they could have an option to just do the priming with the colour after the missing colour - but purge volumes get a fair bit more complicated if removing a colour change introduces a more extreme change than was previous present.