Any experiences with dual extrusion and PVA?

[foehnsturm 969]

It looks like printing PVA is kind a nightmare. I managed to get good printbed adhesion and to print slow enough to get reliable results. Also I learned that fans are a no go.

But once PVA support starts on top of a PLA surface there's virtually no adhesion. Hey that's the main use case why I would consider using PVA ...

Any good advice?

[Dim3nsioneer 557]

Hmmm... maybe the adhesion between PLA and PVA can be influenced with the thickness of the first PVA layer? Please don't ask me how to do e.g. a thin first PVA layer on top of PLA with the current software but it might be interesting to see if this is a way physically anyway.

Maybe rising the ambient temperature helps? Are you currently printing with an open printer at room temperature? What about a heated chamber for that purpose?

Just ideas...

Edited March 30, 2016 by Guest

[foehnsturm 969]

Don't ask how long it took ...

However the result looks ok.

Edited March 30, 2016 by Guest

[ultiarjan 1,223]

time to unwrap it

[Dim3nsioneer 557]

So what was the solution now?

[foehnsturm 969]

No real solution yet. So far:

Forget slicer created supports. Just make up a simple box shape and do a bolean subtract with the part. Use the remaining as support.

PVA doesn't stick to PLA. So, if you print PVA on top of a PLA surface make sure it isn't an island but instead connected to some PVA structure nearby. It will still curl up and need some millimeters height to recover.

I don't use stuff like priming towers. In this case there had to be to separate towers because of the poor adhesion I think.

Edited March 31, 2016 by Guest

[Labern 774]

I have heard PVA doesn't wash off that easily as well. Have you experienced this?

I guess you wouldn't want PVA to melt into the PLA as it could dis-color it?? if this is the case then the adhesion between the two would be a difficult balance to allow it to stick but not melt into it.

[foehnsturm 969]

It takes some time but it mostly washes off by itself. But hidden cavities are difficult to clean completely.

Edited March 31, 2016 by Guest

[foehnsturm 969]

Overhangs are ok. Surface is a little rough even on vertical walls. The adjacent PVA affects the PLA surface. Should use an offset shell operation next time before subtracting the part, so there's some gap in between.

Edited March 31, 2016 by Guest

[SandervG 1,521]

hmm.. I thought PVA should have some bond with PLA.

Have you tried different types of PVA, could there be a difference?

Have you tried your PVA with ABS? Is there a difference?

[foehnsturm 969]

Faberdashery PLA & Scaffold

Support could be removed very cleanly within 5 mins. The print shows impressive surface quality at overhangs.

[Dim3nsioneer 557]

Can you please add a picture from below... that't the interesting side...

[foehnsturm 969]

from below

from above

[Dim3nsioneer 557]

Looks really nice... thank you. I guess you had no gap between PVA and PLA?

[foehnsturm 969]

I set the distance to 0.05mm

[Dim3nsioneer 557]

Was that the results of some tests or just an educated guess? I could imagine it looks better than if one would leave no gap.

[gr5 2,172]

Probably the hardest thing I ever printed was a propeller.  This one came out very very nice!

PVA prints up to about 170C which is probably not hot enough to melt the PLA below it. Consider maybe covering the top and front of the machine such that the PLA is at it's glass temp? Not sure if that will help as then you need even more fan.

Maybe instead turn off the fan while printing PVA? And turn the fan back on when printing PLA?

[foehnsturm 969]

Maybe instead turn off the fan while printing PVA?  And turn the fan back on when printing PLA?

 

That's one of the feature requests I have for new Cura. The other one is a dedicated printing speed setting for support bottom layers (especially those on top of PLA). But I'm still collecting ...

[foehnsturm 969]

This looks promising for the first time, thanks @gr5 for bringing up the temperature aspect. Now printing Scaffold with 215°C instead of 195°C (E3D claims it's good for 190-220)

Fingers crossed ...

[foehnsturm 969]

... and still collecting feature requests:

I had to set support / horizontal expansion quite high (3mm) otherwise support would sometimes start with super tiny blobs on a slanted surface (which don't stick at all). Obviously now all support structures are inflated but the intention is to modify only the tiny ones.

[foehnsturm 969]

... worked out somehow. Don't ask about the ugly surfaces, I took it from GrabCad and it's not designed for 3D printing.

This one is pretty easy

Edited April 26, 2016 by Guest

[foehnsturm 969]

Trying a real challenge now

Support starting on a curved and slanted surface and inside the tube as well

[foehnsturm 969]

For some reason Scaffold extrusion is not that consistent (maybe I should disassemble the feeder...). But besides this it could become a success. Btw, the two support structures on the left aren't  connected, the upper one just starts on top of the pipe.

Edited April 26, 2016 by Guest

[foehnsturm 969]

[gr5 2,172]

>Now printing Scaffold with 215°C instead of 195°C

In your photo with the support on top of the tube - it looks like it worked, right? Was it simply raising the temperature?

Are you using your crossflow fan still? Or is this tube a "zero fan" print?