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prusa3d / PrusaSlicer

G-code generator for 3D printers (RepRap, Makerbot, Ultimaker etc.)
https://www.prusa3d.com/prusaslicer/
GNU Affero General Public License v3.0
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Propagation of retraction to idle extruders on single nozzle multiple filament set-up (bowden) #5355

Open edolis opened 3 years ago

edolis commented 3 years ago

Version

2.2.0

3D printer

Geeetech A30T

Behavior

Hi everybody. I've got a single nozzle - 3 filament bowden style hotend and I am experiencing known issues with stringing when printing with one of the three only. I have tweaked retraction increasing the acceleration -it appears the improvement is linked to how fast the filament is retracted, rather than how much it is - but the problem is not yet solved - there is obviously a limit on the acceleration increase and on my large frame printer having 70cm bowdens, the effect is diluted.. I believe that the issue comes from the fact that there are three filaments running in the same chamber and, currently, if you use just one of them for printing the speed and amount of retraction are not enough to reduce the chamber pressure fast enough- I believe the reason is that the retraction causes the melted filament to move to the chamber by the other two idle filaments before enough depression is created to prevent oozing and stringing on the nozzle.

Now, the request would be being able to "propagate" the retraction to the remaining (idle) nozzles, possibly by a percentage of the main nozzle(see below for detail), so that you can control color poisoning and "crank up" retraction of the idle nozzle as much as required to support the active nozzle and get to the result of no oozing. The effect would be amplify the acceleration of the mixing chamber pressure reduction using multiple extruders (see table below for what I mean)

This would also allow to reduce extruder acceleration, which I have pushed to the filament grinding level which is not good. Obvioulsy de-retraction should follow suit.

Do you think this feature is feasible? I think this is quite important to help users of multiple filament nozzles, particularly on large frame printers where the bowden pipe is long, which makes retraction on just one nozzle even less efficient.

Thanks!

Example

For instance (I believe I interpret the working properly, please correct me if I am wrong)

image

edolis commented 3 years ago

Ahem, any chance some good soul points me to the function in the code handling retraction?