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philippaulth

What causes BB print core to block?

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Hiya,

We've been printing pretty successfully with our UM3+ for the last few months, but this week the BB core (printing PVA support) has blocked twice. The first time we had to dismantle the print core (I know this isn't 'authorised' - but we found that out afterwards! :-) ) and managed to unblock it with a very thin drill bit. The second time it stopped printing support midway through a print and seems to have blocked up again. I tried to clear the blockage by heating the print core to 220C and pushing fresh material through by hand, but it wouldn't budge. Disassembling it again we managed to get the blockage out, however the bit we removed wasn't really burnt up so I'm at a loss as to what went wrong.

Our best guesses so far:

1. The PVA has 'taken on' humidity and it's burning this off in the core, causing debris

2. The temperature of the PVA core is too high (but I am using the Cura defaults)

3. Some dust/dirt/plastic got in to the print core and has now damaged it

4. The first blockage was a fluke, and we've damaged the print core now by disassembling it

5. The BB core has run it's course and worn, and just needs replacing (though we've not used even a whole PVA reel yet)

6. The blockages are happening because the filament is grinding, and then the PVA burns up in the print core as it can't extrude.

In both cases there has been grinding on the filament, but as we've not been there to witness the moment the blockage occurred we can't tell if the grinding was caused by the blockage or the blockage caused by the grinding, if that makes sense. I loosened the tension on the feeder a while ago to resolve another grinding issue.

Can anyone shed any light on this? What's the most common cause of blockages on the BB core?

Thanks for your help,

Hayley

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I don't know the answer exactly but you are on the right track.

#4 - don't worry about that. It's either obviously broken into too many pieces or it's fine.

It could be dust. Its more likely grinding happens first.

Does it make popping bubbly noises when it prints? If so that is the sound of boiling water. That could esily be the problem as it produces too much head pressure (maybe) which causes grinding (maybe) and then the pva bakes in the nozzle for 20 minutes when no one is paying attention and clogs.

Unfortunately it might not be possible to dry it. I'd read up about how other people dry their pva but I suggest you buy some new pva and keep it in a box with dessicant even while printing with a hole to let the filament out. Or at least store the pva in air tight bag when not in use even if just for a few hours.

nylon is pretty easy to dry. Not sure about pva.

Meanwhile until you get a new reel read about how other people dried their pva and also lower the right core by 5C.

Also consider getting a "hardcore" form 3dsolex because then you can just change nozzles and clean them by soaking them for a few days (disclaimer I sell 3dsolex products in usa).

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Hi @philippaulth

It could be that there are still some residues of filament in your print core after a failed print that block proper extrusion of your PVA. Please follow these instruction to clean your BB print core: https://ultimaker.com/en/resources/23132-clogged-print-core.

Let me know if you succeed. I recommend to continue with the default profiles and the BB print core.

If you would need to dry your PVA, follow these instructions:

Heating the filament for 2 hours at 45-55 °C. The easiest way to do this is by putting the spools on the heated build plate at the required temperature (45-55 °C). Warning: do not use a household oven. Make sure that the PVA filament has cooled to room

temperature before inserting it into the 3D printer.

Alternatively you can add multiple bags of the fresh desiccant in the sealed box/bag with the filament.

Good luck.

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If it's getting blocked midway through a print, I'd say the humidity is your most likely option. I had some PVA that had been left out for quite a while (weeks) that I was testing with. On Friday I successfully ran a 24 hour print. By Monday it it had finally reached the point where it had absorbed enough humidity that my next print failed.

As far as disassembling it goes, I think it's really easy to damage with disassembly and not see it--it doesn't take much to twist the double heat break just enough to disturb the flow of the filament. However, I think if that was the case, you'd be seeing the print fail sooner.

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