[printing into air ("thick stringing")]

Hi all,

 

I noticed that our UM3E exhibits a form of stringing I have never seen: it looks like the printer is still printing in during some of the travel moves:

(check out the crown): 

 

 

Note that there is a couple of other things that went wrong with this (PVA nozzle blocked midway, the head of the dude on the left fell off and there is a really notable z-scar). 

I don't know of the z-scar and the "thick-stringing" are related. I suspect there must be something wrong with the retraction settings?? But even if retraction was off completely, this would just lead to normal stringing, not fully extruded filament in thin air. 

 

Has anyone come across something similar? 

 

Cheers!

[Rough surface with PLA+PVA print]

I got a chance to play around with it a bit more and I am starting to suspect that the fault is actually just with the PLA, while the PVA is making it difficult to diagnose.

I printed the same geometry with big support-xy-distance, small support-xy-distance and no support (see below)

Sorry for the bad quality of the images, this was taken with my phone.. But you can still make out the important stuff:

 

the two prints on the left look very similar, even though they had a different support xy-distance. I think that if the PVA was at fault, they should look different. 

The print without any support shows that the PLA is stringing. I wasn't able to see that when the PVA was in the way as it significantly decreases stringing. That wasn't immediately apparent to me, but now it seems kinda obvious. 

 

Since other prints come out perfectly fine I suspect the stringing is mainly a retraction issue rather than a temperature issue. These are the settings I have ben printing with: 

 

 

will play around with those when I get the chance

 

[Rough surface with PLA+PVA print]

Thanks for the advice! A lot to go through.. 

My print settings are the same as in that screenshot, so that is fine. Also I am pretty sure that the support roof/floor isn't the problem as the stringing is more (or equally) dominant on the surfaces that aren't overhanging. 

 

12 hours ago, kmanstudios said:

Also, some of your stringies are able to be taken care of with the wave of a heat gun. Finally, without any size comparison I am looking at the line widths you say you sliced at (Fine = 0.1mm) so I am guessing that the thinness of the edges are not much larger than 0.3 - 0.4mm in thickness. So these could be really tiny imperfections.

That is correct. The faults are quite small (but detrimental to the overall look). I haven't tried using a heat gun yet! 

 

11 hours ago, kmanstudios said:

But I see a lot of difference on what would be assumed the underside of the arch print. In the orientation of the pic, it would not need support. But if it was an arch with the flat sides down and the arch going over, the side you listed as having support is straight and consistent on the corners (from underarch to side walls) while the other side is wiggly and loose until there is enough density to merit a surface to build off of and the corners between the underarch and sides are straggly as well until it has enough density to build upon.

Yup, that is correct. I laid the arch on the side so you can see the underside. 

 

2 hours ago, kmanstudios said:

I am curious, if you printed with the UM2 without PVA, what were you using for support? Also, have you played with your retraction and temp settings for the PLA as well?

woops, that was a typo. It was actually UM3. I was using PVA for support. 

 

Retraction and temp settings are a good idea. Will play around with them as soon as I get the chance! The printer is shared with a couple of people so I can't just play around with it whenever I want. 

[Rough surface with PLA+PVA print]

2 hours ago, gr5 said:

I'm curious if the PVA was making a solid layer just before the PLA was printed on top.  There's an option related to that in cura somewhere.

 

No, it didn't. I had the brim printed in PVA, but the first layer of the model itself was still PLA. 

 

I am not certain that the PVA is what is causing the imperfections. I tried to print an arch with PVA support on one side and no support on the other and both sides came out perfectly fine. If anything, it looks like the "no-support"-side has a similar roughness artifact on the non-overhanging side:

 

That being said, I tried to print my complex model again and it came out worse. This time, instead of just having the PLA "bumps", it also had holes of similar size and shape. I feel like this is where PVA was inside the printed geometry, similar to what I imagine JohnInOttawa was talking about.

 

I will keep experimenting, but it would be super helpful if someone else has come across this previously  

[Rough surface with PLA+PVA print]

Thanks for the advice!

 

I haven't dried the PVA yet as it was fairly fresh out of the packaging. By that I mean it was out for a few days. I have no feeling for how long PVA can be outside before moisture becomes a problem. I guess it depends on the ambient moisture. But how long can I go without worrying if the ambient moisture is "average"? It is in a semi-sealed box to protect it from dust in the workshop. It gets pretty warm in there. Since there are no water sources inside that box, I would assume that the high temperature would decrease the relative humidity and hence be good for the PVA. But I have no experience with this at all. 

 

I heard that PVA turns from translucent to opaque once it has a higher moisture level. My support structure was still translucent, so I am assuming humidity was not an issue here.

 

The extrusion temperature was 215˚C, which is on the lower end of what Ultimaker recommends. However, the internet usually talks about lower temperatures like 190-200˚C. I haven't tried playing with this yet. have people found this to affect the PVA support quality?

 

Ultimaker says that PVA should be stored below 28˚C. This is clearly not the case for me.. However, the glass transition temperature of PVA is 85˚C, so I don't see where the 28˚C is coming from (except for the humidity concern?). 

[Rough surface with PLA+PVA print]

I don't seem to be able to edit the original post anymore？ Anyway，here it is！

[Rough surface with PLA+PVA print]

Hi all!

 

I am trying to print a PLA+PVA (AA0.4/BB0.4). The PLA has a partly rough surface, which I have never seen when printing on UM3 without the PVA.

After dissolving the PVA, the print looks like this:
 

 

This is printed with the standard Cura "Fine" profile (without prime tower). 

 

Has anyone encountered a similar problem and has been able to fix it?

 

Cheers!

T