Feature Request: multi-extruder, single nozzle, without prime tower

[goddone 0]

The motivating problem: I have recently experienced frustrating print failure at near-completion of a large, tall 2-color PLA print on a Creality CR-X (2 extruders, 1 hotend)—the problem is that even with a large prime tower footprint, when it gets tall (200-300mm), the torque from the printing pries the prime tower loose while adding layers.  Also, it is extremely wasteful of material.  

 

The solution (a new feature): It occurred to me that the prime tower would be completely unnecessary if the G-code would instruct the machine to perform filament switch before finishing one color so as to push the leftovers out on that same color, and then prime the next color into the interior of the part, for example fill or inner walls.  In this way, the primings are integral to the object being printed, resulting in zero waste and more robust printing.  This feature could be implemented in Cura with perhaps a checkbox and 2 parameters (the length to continue extruding after filament change and the volume to prime, which is already a parameter) and some programming to sequence the operations near a filament change.  There may also be the need for a feature that warns the user if there is not enough infill or inner wall to handle the desired priming volume.

 

Best Regards and thanks for the sweet software!

Gian

[Brulti 177]

That's interesting but you run the risk of the part being knocked over when the priming is done on the inside and the printhead is wiped against the inner walls. Or to have small bits of filament sticking out of your part and messing up the layers and the coloring, in case the priming isn't perfect and tehre's still some leakage.

 

It's been suggested to UM to make the prime tower conical: wider at the base and thinner at the top, to give it even more stability with the round shape, I do not know if this is on their todolist and would be implemented in Cura 4.0 or later, or maybe it is on list of things that would be nice to code but are not considered that important.

 

 

[goddone 0]

Thank you, Brulty.  I appreciate your points on that.  I have found that this issue of oozing can be easily addressed as follows.  At extruder switch, active extruder is retracted 100 mm by setting position to -100.  Then tool is switched to next extruder and instead of setting position back to 0 (thus reversing the complete 100mm retraction), the position can be set to -5 so that there is no oozing.  Then the risk is only of missing a small bit of material on the infill, which I do not forsee to be a problem.  The machine already retracts and de-retracts many times during a print.  An extruder switch would be no different.  Of course, this would not be universally applicable to every conceivable print, but gosh would it save a lot of waste material from the environment and save a lot of headache with failed prints.  In my case, the print has a wide base, so it is not nearly as susceptible to knocking over as the prime tower.  Another benefit would be that build space would not be taken up by the prime tower.

[Brulti 177]

In my experience, using a UM printer with UM-brand filament, prime tower have become useless. I guess it should be possible to find settings with any combination of printer and filament to make the prime tower useless as well, thus saving a lot of time and material.