overextrusion using 2 extruders (pla with pva)

[b16ior 0]

Hi all

 

i'm a french student in electronical engineering and for my tutorship project i have to print a reflectarray (telecommunication)

this project needs extreme printing accuracy and i have trouble finding the right settings. Also i'm working on a ultimaker S5 with ultimaker PVA and generic PLA 

 

so the main probleme i have is when printing with pla (AA 0.4) and pva (BB 0.4) to support my structure.

What's happening is that when the printer is changing materials lets say from PLA to PVA ,a bit of PLA is still coming out of the extruder, so when changing again from pva to pla it puts too much materials. I've tried the setting "retract at layer change" but didn't get good results

 

here is some picture so you can understand better 

 

So this is a print whith PLA support and i'm pretty satisfied with the quality but wasn't able to remove my structure from the support (it's very thin so it must have melted together) 

so i've tried with PVA but this is when the probleme of overextrusion occured 

as you can see there is some overextrusion when changing material so when changing materiel it create a sort of blobs on the sructure 

 

here is the strucure after dissolving pva as you can see the quality is far from the first print when using just one extruder 

 

I've thought about using pla from ultimaker or change the support for breakaway anyways i'm gonna continue to test with different setting but maybe you guys can help me 

 

Thank you for your helps 

Cédric 

[tinkergnome 926]

7 hours ago, b16ior said:

when changing again from pva to pla it puts too much materials

 

The prime tower is meant to deal with any flow inaccuracies, so that anything is nice and equalized when the extruder comes back to the actual object.

 

My advice is: if it really needs to be printed in this orientation - enable the prime tower (or use a bigger one). Place it near the printed object.

 

Although - the part looks like it could be printed upright  - and without support structures. Would this be an option?

 

BTW: which nozzle size is this printed with? 0.25mm?
 

[b16ior 0]

hi,

 

Sorry for the late answer i was really busy with exams this weeks and thanks a lot for your advices !

 

I've tried with the prime tower and it was exellent. I'm printing with a 0.4 AA i'm not sure i have a 0.25 available at my lab but will definitely ask. 

 

I didn't know you could place the prime tower near the printed object so i will try to cut some print time maybe ? 

 

I've noticed that i'm almost hitting the object when the nuzzle is going to the prime tower so i thought about checking the z-hope when retracted parameter or the z hope after extruder switch. 

 

Your idea of printing the model downward could be very nice the tricks is that my part is similar to a plate so what coold be the best for printing a plate upward or downward ? 

 

Thank you again for your concerns 

 

Cédric,

 

PS: i'm gonna post photos of my project so you guys can follow my advancement 

 

[gr5 2,094]

1) Please post your project file (which will include the model).  Or at least post the model.  I don't understand the shape.  Is it supposed to be spherically curved?   (in cura "file" "save project as").

 

2) Putting the tower closer to the part doesn't just save time.  During that travel time the nozzle can leak.  The shorter the travel, the better.