I’ve noticed if I complete printing an object that last uses a dark filament then start a new print with a much lighter one (black to white being the extreme but not limited to that) that there is insufficient purge of the old color during the get ready stage of the printer before starting the new object.
This results in the first part of my new print having a darker color than it should do before the filament runs to the true color.
Has anyone else experienced this ? Is the printer capable of remembering what was last used on a print and adjusting the purge at startup as necessary ? it seems unlikely, especially if the printer is turned off in-between.
I could add a few lines of skirt round the object but not all objects are large ones. Any advice on how to get around this issue would be much appreciated.
The slicer tries to calculate how much pure to do based on the filament colours (e.g., less purge white → black than black → white), but it isn’t perfect. You can adjust the purge volumes between colour changes using the “Flushing volumes” button on the “Project Filaments” section. The easiest thing to do is to bump the multiplier but you can also edit the colour transition matrix directly.
I should add that this is mostly for AMS prints, but it might also work for starting a new print. I’m not sure if there’s a way to specify just the purge volume when it first loads a filament on print startup, but that does seem like a reasonable thing to want to be able to do…
Update: I looked into this more for the initial startup purge. It’s triggered by the M620.10 command in the startup G-code. I wouldn’t actually touch this section since M620.10 doesn’t provide any direct method to actually increase the purge. One could add a second set of purge commands or add a command to advance the extruder and then wipe, but I won’t go into details since I haven’t tested any such changes on my own machine and generally don’t encourage editing the startup G-code since making errors doing so can damage your machine.
Not a tidy solution, but maybe a workaround would be to add a small object out of the way on the build plate to print first.
You could also manually load the light coloured filament and then manually purge some before starting the print.
Also are you sure the contamination is extruded and not residue on the build plate? I have some white components with a red stain on the underside where I’d been printing red on the previous print.
Thank you all for taking the time to look at this and reply.
To answer a couple of questions the discoloration appears on the top and bottom of the layer. It’s not due to residue on the plate. I’ve tried maximising the flushing volumes for a couple of sample colors and testing but that didn’t help though it does do the job when printing a multi-color object and changing from/to the same filament colors.
It seems the answer is to manually purge before starting a new print if I know I’m likely to have issues.