PVA printing issues, adhesion or BBcore problems?

[martinstyner 2]

For the last several weeks all my prints with PVA support failed. They print well for the first few slices and then fail, though it is unclear why (bunching up of filament, lack of adhesion). As the BB 0.4mm core was already older than 12 months, I replaced it with a newly ordered one and used a fresh (ultimaker) PVA filament role. Same problem, though it prints well for a bit longer.  I printed the X-Y calibration and the horizontal pattern looks all fine, but the vertical lines are mostly missing (see attached photo).

I don't think it's an adhesion issue, as I tried the XY calibration both with my usual adhesion (magig glue) as well as painter's tape, and both showed the same pattern (good vertical, missing horizontal lines).

I also replaced the PVA role with white breakaway filament and the calibration print with the same print core (even though ill-suited to print with the BB 0.4mm core) was all fine. I am somewhat at my wit's end and do not know what else to try.

 

Could it simply be quality issues with the PVA filament (leading to inconsistent adhesion) and I need to order another role and try it again?

 

Any help is appreciated

Best

Martin

 

[gr5 2,238]

Well you changed the BB core so I think it's probably the PVA itself.  I think it got wet.  Maybe even before it arrived to you.  It would help if you could show the first layer better.

 

Also, do you have the Material Station?

 

keeping PVA dry

 

So PVA is very different from PLA.  It's harder to print.  It doesn't stick to itself so amazingly well like PLA.   keep it with 1/4 liter (one cup) of dessicant at all times.  I NEVER leave it overnight on the printer, etc.

 

One sign the PVA is too wet is it snaps and pops and hisses and you can actually often see steam coming out at the nozzle tip while it prints.  The PVA ends up being snowy instead of clear because it has tiny steam bubbles embedded (hence the snowy look).   If it's only a "little" wet you won't notice the noise or steam but it will still be snowier than usual.

 

When PVA is wet like this it expands too much and so it overextrudes.  Enough to get lots of stringing and other issues (sometimes it doesn't stick well to the print bed).

 

It's easy to fix with heat.  In cura look up how many meters of PVA are needed for your print.  Unspool that much, place on the heated bed, put the spool on top (no need to cut the PVA).  Put a towel over all that and another blanket on top of that and heat at 65C for 4 to 8 hours.  That should be enough to get you going on your print.  To dry the whole spool, dry it for 24-48 hours (not necessarily all at once).

 

Going forwards keep it in a 2 gallon zip lock with LOTS of desiccant.  And recharge the desiccant every month.  I buy it in liter jugs and store it in a container with a lid that stops the desiccant from coming out but allows air exchange.  I use color changing desiccant that can be reheated (dried) in the microwave.

[martinstyner 2]

Thanks, I tried to dry it out (8 hour drying at 65C with towel, unspooled plenty, more than enough for the calibration print, which I am using as it only prints a few layers) and the result did not change. The attached photo shows a closeup , the vertical lines were not printed at all and the horizontal lines are spotty, rather than nice and clean. This print had plenty of magig-glue on it (i do not think it's adhesion).

 

The issue seems to be though less one of over-extruding, but under-extruding.

 

I will do another one with the spool having been dried for 24h.

 

Btw, I do not have a material station, but i put away my PVA after each print job and keep it in a sealed plastic bag with desiccant (though I could probably use more of it).

 

Could it be the feeder that needs replacement? Before I try that, I will order a new spool of PVA and try again with that one.

 

Best

Martin

[gr5 2,238]

There are tons of possibilities.  humid filament is unlikely at this point.  I don't recommend buying more PVA.  If you are going to buy something consider buying "breakaway" filament (if your model can work with that kind of support - some models have too many inner caves where you wouldn't be able to remove the breakaway).

 

Well it seemed to print much better for the second part.  So I'm thinking the filament wasn't all the way installed.

 

Before installing the filament I always cut it to a point using wire cutters.  I do two angled cuts to make a point.

 

I always choose the MOVE command in the printer menu and then left the lever on the feeder, slide the filament all the way in, wait for it to get above 160C and then start to use the down arrow in the move feature.  While doing this I feel the filament on the back so I can tell if it is truly moving or stuck.

 

Once the nozzle is at temp you can make a zig/zag in the filament near the nozzle and then see how quickly you can get it to reach the bed.  If it can reach the bed in 5-8 seconds you are fine.  Even 10 seconds isn't too bad.  If it takes more than 12 seconds then something is probably wrong.

 

Let's assume it's fine at this point.  Well now we also know the filament is fully loaded so try the print again.

 

There is a bug in some versions (all versions?) of the firmware when you abort a print or certain special cases (calibration test?) where it retracts the filament a bit too much and if you abort twice in a row the filament doesn't get into the nozzle until you've been printing a few minutes.  I'm thinking either you didn't load fully or it's that bug.

 

The above tests should allow you to distinguish between several different types of problems (be sure filament extrudes quick enough, be sure it's installed all the way).

[martinstyner 2]

Took me a while to try different things out, but unfortunately no improvement.

 

While I have breakaway filament, and love it when appropriate, it does not work for this print (and for most of my prints), as the 3D models have folded, internal parts that are unreachable, and thus the breakaway filament cannot be removed. But PVA is perfectly suited for the job (and I have been printing regularly in the last 2 years).

 

The problem seems to be with advancing the filament. It always starts out well when loading the PVA (reaches the bed withi less than 10 seconds). Also, I can push it well through the nozzle manually. But then after the first 1-2 layers are good, less and less filament flows. The printer then realizes it (I assume the flow sensor) and pauses the print as it thinks it ran out of PVA. I can then unload/load the PVA and try to continue, but that is not working well as it has already missed 1-2 layers of PVA.

 

So, the PVA is well loaded when I start the print (it was extruding nicely), but then it slows up during the print.

 

I think that the feeder might have an issue and I think about replacing it next.

[gr5 2,238]

The feeder stepper is probably fine but the feeder internal gears and such could indeed have an issue.

 

The feeder stepper driver could also be overheating (never heard of this being a problem on an S3 though - it was a problem on some Ultimaker 2's if it was in a hot room).

 

The first 1-2 layers are printed typically a lot slower and also with the fan is off and each layer the fan speeds up a little more.  And if I remember correct, each layer goes a little faster for the first 5mm (I could be wrong on this).  So it's not unusual for failures to occur as the printer speeds up (and the nozzle cools down).

[martinstyner 2]

Followup with outcome: It was the feeder. I ordered a new one, and as I was replacing the feeder, I realized that the tension spring was not correctly "tensed"/screwed down, so the feeder was not putting the proper tension on the filament and thus had trouble advancing it. (This happened at the last maintenance of the feeder,  I forgot to re-tense/screw it to the proper line). I feel really dumb for not catching this earlier.

[GregValiant 1,359]

" I feel really dumb for not catching this earlier." 

Aaahhh, but in your favor - you let everyone know where the problem was.  Thank you.  I think that makes it a wash.

[jgehrer 1]

Im having the same problem on my s3 and just got an s7, first test with PVA printed ok and the second one failed (material error) after about 5 layers.  Will try the tension on the new machine and see if it works.