PVA print blobs/bulbs and strings

[AdamSJ 0]

Hi all,

 

We just got our Ultimaker 5 at the office and it's super exciting! Right now we're trying to print a handle, but we're having some troubles printing with PVA as the support material. The other material in this case is Tough PLA. The print creates these blobs/bulbs and strings (for a lack of a better term) both ejected on the glass plate and on the support structure itself. Since it takes about 2 days to print one handle I figured I should read up on the settings and what could be the cause. So far I've only found that Ultimaker recommends:

 

"When printing PVA in combination with another material, we recommend using the adhesion method for the accompanying material. For the best adhesion and print quality, we recommend setting the ‘build plate adhesion type’ to Extruder 2 (PVA) in Ultimaker Cura."

 

I'm yet to try this setting. Does anyone have any experience with that setting? Does it make it better? As we're just begining to learn the machine and Cura we're not exactly sure how to get rid of this problem. Do any of you people out there with more experience know if this issue could be circumvented with some Cura settings?

 

Edited March 5, 2019 by AdamSJ

[kmanstudios 1,120]

31 minutes ago, AdamSJ said:

The print creates these blobs/bulbs and strings

On the PVA or on the TPLA or both? The PVA can be that way many times without creating an issue. I routinely get a bunch of little PVA crud at the buildplate like it is shedding.

 

31 minutes ago, AdamSJ said:

Does anyone have any experience with that setting? Does it make it better?

I routinely use the PVA brim. Its major advantage is that it keeps you from having to manually trim the brim and you get a clean edge at the print/plate junction.

 

Edit:

The PVA brim only works with materials that will adhere to the buildplate well on its own.

Edited March 5, 2019 by kmanstudios

[AdamSJ 0]

2 minutes ago, kmanstudios said:

On the PVA or on the TPLA or both?

 

I routinely use the PVA brim. Its major advantage is that it keeps you from having to manually trim the brim and you get a clean edge at the print/plate junction.

Only on the PVA.

 

I'll try the PVA brim some time next week and see if it makes it better. But since it creates these blemishes higher up on the handle as well I don't think it'll fix it all.

Edited March 5, 2019 by AdamSJ

[kmanstudios 1,120]

43 minutes ago, AdamSJ said:

But since it creates these blemishes higher up on the handle as well I don't think it'll fix it all.

The brim only will work with the fact that the model comes off clean when dissolved.

 

As far as the PVA having strings/blemishes, it is not an issue as long as it does not interfere with the other material.

 

The only time to really have a worry about PVA is when it gets lacy and not printing a solid wall.

[AdamSJ 0]

2 minutes ago, kmanstudios said:

The brim only will work with the fact that the model comes off clean when dissolved.

 

As far as the PVA having strings/blemishes, it is not an issue as long as it does not interfere with the other material.

 

The only time to really have a worry about PVA is when it gets lacy and not printing a solid wall.

I see. Thank you!

 

It's not a problem in this particular print but there's a potential that the PVA blobs/strings inteferes with the TPLA material in the future. The PVA could be intertwined in the TPLA if it gets "ejected" from the printer head and lands on the TPLA material wall. I haven't seen this happen yet but it seems likely since theres so many blobs/strings laying about on the glass plate. So if there's a solution to not get these blobs/strings it would be good. But you don't think I have to worry about it?

[kmanstudios 1,120]

14 minutes ago, AdamSJ said:

But you don't think I have to worry about it?

Not generally. At some point, it may get caught in the other material and create little holes that make the model not watertight. But my experience so far with the TPLA is that it has not created this issue for me since TPLA was released. So far, I have only used the UM TPLA. This is one material I really like and see no reason to go with other brands.

 

Also, remember, PVA is just a pain to print with even in the best of circumstances.

 

This is a link to a post that addresses an issue that may arise because of, well, several reasons:

 

Edited March 5, 2019 by kmanstudios

[AdamSJ 0]

Many thanks, kmanstudios! I'll take a look at the link. 

 

You say PVA is a pain to print, do you have any other support materials to recommend? 

[kmanstudios 1,120]

4 minutes ago, AdamSJ said:

Many thanks, kmanstudios! I'll take a look at the link. 

 

You say PVA is a pain to print, do you have any other support materials to recommend? 

Depends on the model involved. My stuff is usually delicate and spindly in nature. So, PVA for me so far. My stuff is more art oriented and not functional parts like most people's stuff.....

 

If solid and not delicate, you may want to try the breakaway material.

[AdamSJ 0]

New day, new challanges. Today when I looked at the print (it's almost finished now) a part of the support structure had been seperated from the rest. Has anyone else ecountered this problem and have a solution? It looks like the support structure eventually sorted itself out and carried on normally from there and won't cause any problems this time. But my gut feeling says this could cause problems in the future. 

 

The reason for printing the handle standing is to get the surface finish as good as possbile. We've tried printing it laying but then the layers were clearly visable.

 

 

[helmut92 1]

I also had some problems with the blobs and strings.

I think that was because the pva is hygroscopic. We have an oven here at work that is on 24 hours a day at 40 degrees. I stored the pva there over night and tried it again the next day. it worked great then without blobs and strings.
Since then i have two pva coils and change the coil every time i start a print. The unused one comes in the oven. 

[kmanstudios 1,120]

It seems to have separated a bit on a 'thin' area where it would build on, but then seemed to recover and actually support the area it needed to support. The real question is what does it look like when the PVA is dissolved?

 

Ultimately, that is the only real question: What does it look like when the PVA is dissolved?

[AdamSJ 0]

3 minutes ago, kmanstudios said:

It seems to have separated a bit on a 'thin' area where it would build on, but then seemed to recover and actually support the area it needed to support. The real question is what does it look like when the PVA is dissolved?

 

Ultimately, that is the only real question: What does it look like when the PVA is dissolved?

Exactly. I'll wait and see how it looks underneath. Hopyfully it hasn't effected the print. 

Is there a rule of thumb of what you can do when you have a thin wall of PVA like this to stop this from happening? 

[AdamSJ 0]

2 hours ago, helmut92 said:

I also had some problems with the blobs and strings.

I think that was because the pva is hygroscopic. We have an oven here at work that is on 24 hours a day at 40 degrees. I stored the pva there over night and tried it again the next day. it worked great then without blobs and strings.
Since then i have two pva coils and change the coil every time i start a print. The unused one comes in the oven. 

Thanks for the info. I've read about putting TPU in ovens since it's hygroscopic but didn't know PVA had the same properties.

[Bigbrit 9]

So here's my experience over the last 8 months or so.

 

PVA is a pain in the arse.  It's super hydroscooic, it prints in blobs and strings etc and it's very expensive.

 

I have found that for best results I print supports from extruder 1 and only print an interface layer of PVA from extruder 2 where support meets model.  This has several advantages, it's cheaper because you use less of it, its quicker because the machine doesnt need to keep swapping nozzles, and it has less chance of causing problems.

Edited March 6, 2019 by Bigbrit
Spelling

[RudydG 62]

Good idea!! will try this also. (only the interface support with PVA i mean)

Anyway, i now use PVA a lot, but i am very carefull with it, i use a drybox (Polymaker), and cut the needed length for the print, the rest goes back in a drybox or sealed bag with silicagel. Blobs and little pieces are a fact of life with PVA.

In the past is used the breakaway a lot (still use it sometimes), but for delicate pieces it is not so suitable. And it is a mess to remove also.