Printing with Polymaker PolyCast (PVB) Filament (Mk4)
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Printing with Polymaker PolyCast (PVB) Filament (Mk4)  

Estimable Member
Printing with Polymaker PolyCast (PVB) Filament (Mk4)

The last couple of days I have been printing with PolyCast material which is very handy for y'know, printing of items that are to be "investment cast".

The first set of objects printed just fine, but the last bed of items took over 12 hours to print.  At the end, I unladed the filament and slung it straight into the dry cabinet at RH <1% for overnight storage.
The next day I sent to do the next item. I dried the filament, because it had become brittle.
I found I was unable to load the filament, no matter how many times I tried, and I went down the road of nozzle clearing with Acupuncture needs, heating the hotend to 275 degrees & etc. and still no go. I also found bits of filament in the filament drive system, discovered by poking a length of filament down the hole with idler door open.
Since I needed to get on with the print, I decided to change the nozzle.  In the process I discovered that the nozzle long tube was filled with filament, it had broken off at the end of the tube, presumably when it was unloaded.  So that nozzle has now been replaced, and the old nozzle got placed in a bowl of IPA (because PVB is IPA soluble), and hoping to clear it that way.  It's an Obxidian nozzle, so expensive.
I surmise that the tube has a blockage of filament, somewhere higher than the nozzle (further than the length of an acupuncture nozzle).  Perhaps the previous print incurred heat-creep without my being aware of it.

So, in summary, a lesson for me.

1. PVB filament evidently adsorbs moisture more than most, and even after only 12 hours of printing it had adsorbed enough to become brittle, and break when it was unloaded.  Not something they (Polymaker) put into the otherwise comprehensive  user guide.  Actually, they do not even mention that its PVB, Google told me that.

Maybe this will help someone else.

Posted : 13/10/2023 6:09 am
Estimable Member
Topic starter answered:

Obviously this topic not deemed worthy of a response.  But I do have an outcome on this I can share.

Firstly the Nozzle clogging of PolyCast filament using settings recommended by Polymaker wasn't all that helpful.
For example they recommend a range of 1 to 3 mm for retraction without saying why.  I picked 2 mm.
But this means the brittle filament was being pushed down and up again a lot during the print.
Ultimately I found 1.0 mm was better. and a Lift of 0.4mm

Normally, one might find that the filament settings have (say) 215 C for the first layer and (say) 210 C for following layers.  In order to help with clogging, I found it useful to have both 1st layer temp and subsequent layer temp the same value - 215C.  I note that Polymaker indicate PolyCast starts to degrade at 260C, so there isn't much margin.

Clearing of clogs ?  Well I had to clean not 1 but 3 nozzles. I heated them to 250C and pushed the smallest allan key thru the top tube to clear the clogs in upper part of the nozzle (due to heat creep). Then soaked the nozzle overnight in IPA (a solvent for PCB) in an ultrasound bath. It was important to remove traces of PVB clinging to the side of the nozzle tube. 
Then put the nozzle back on the printer and fed it some PC Blend filament at 275C to finally clear the nozzle. But after that, also used PETG filament in a cold pull operation to try to ensure the nozzle completely clean before retrying with PBV. All this x 3 for all of the nozzles affected by clogs.

My MK4 sits in a prusa enclosure that helps with most prints.  But for the PolyCast filament, I found it best to open up the lid and the doors. So the print job runs at room temp. This helps to prevent heat dreep, one of the causes of my clogging.  I also truned on display of heatsink temp on the footer of MK4 display, so I can be aware if temp climbs too high, aiding heat creep.

The PolyCast material is VERY hygroscopic and difficult to dry.  I tried drying it at 55C for 12 hours, when Polymaker recommend 60C for 12 hours, but it seemed to be closest my Print Dry dryer could manage. And still the extruded filament popped and crackled straight out of the nozzle.
Ultimately I had to go that one step higher to 65C for 12 hours, and also to have the filament inside the operating dryer during the print, fed thru a guide tube to the extruder.

In amongst this, I also found that the filament had left bits stuck in the teeth of the Nextruder. Prusa say to clean the feeder gear using a wire brush, but it's impractical. I had to use a dental probe to rotate the gear and clean the teeth, with compressed gas to blow away the dust.

Posted : 19/10/2023 2:11 am
Trusted Member
RE: Printing with Polymaker PolyCast (PVB) Filament (Mk4)

Thanks for sharing your experience. Cleaning a clogged nozzle seems to be a bit more difficult as with the old design. And also the nextruder, which is an improvement for most of the cases, once it get dirty it is much more complicated to clean. Sometimes only disassembling the planetary gear helps. Always pro and cons.

Posted : 19/10/2023 4:54 am