Gizmodorks PVA Stringing

[jcrscott 0]

I’ve been having trouble with extreme stringing using Gizmodorks PVA.  The strands wrap themselves around the shaft of the front fan, and even if I remove the strands from the fan after every print, they eventually kill the fan, which leads to the filament melting above the print head, which jams the material feeding system.  I’ve had to replace the fan 3 times now.  
 

It may seem like a no brainer to just stop using the Gizmodorks PVA but it’s much less expensive and much easier to remove than every other alternative I’ve tried.

 

I’ve also tried enabling retraction, increasing retraction distance, changing print temperature, and changing travel speed. None of these have helped.

 

I’m currently printing the PVA at 35mm/s and 185 Degrees C.  I think it’s important to note that the eSun PLA I use as the primary material has no issues with stringing.

 

Does anyone have any experience with this material, or any suggestions for how I might resolve this issue?

 

Thanks!

[gr5 2,173]

PVA absorbs water like a sponge.  Then when you print it, the water boils and causes over extrusion and stringing and foaming of the filament.

 

I've only used Ultimaker PVA but I imagine any PVA is going to have this problem (nylon also).  Leaving PVA out on the back of your printer for 24 hours is enough that it will not print as well.  And some prints are longer than 24 hours (although if the spool is skinny enough then you are always exposing fresh PVA).

 

do an experiment.  In cura in the lower right corner hover over the "i" and it says how many meters of PVA are needed.  Unspool that much and place it on the print bed with the spool holder on top.  Set the bed temp to 60C and put a towel over it.  Let it sit for at least 8 hours.  Then do the print.  See if you get less stringing.  Don't go hotter than 60C as you can soften the PVA too much.  No need to go cooler than 60C (at least for UM PVA - you can test this by first cutting some PVA from the end and putting on the bed and set the bed to 70C and 60C and put a towel over it - after 60 seconds at that temp reach under the towel and bend the pva - see if it might deform under pressure of a spool on top).

[gr5 2,173]

You might think "but I use the desiccant".  Well you need about a cup of desiccant and you need to recharge the desiccant every month or so.  And you need a humidity sensor as I've thought I've recharged the desiccant but it was still at 30% humidity in the bag.  You need to make sure you are getting much drier than 30%.  You should be able to get down to 15%.

[jcrscott 0]

Thanks so much for your detailed reply gr5!!

 

I use environmental sensors to track the humidity and temperature of my filament and always use dehydrated filament for each new print.  Some of my prints can be VERY long because I like to print "miniatures" (~8in tall) using a 0.25mm nozzle at ~35mm/s.  The print in the images I shared in my first post was 10 days long.  This is the longest print I've ever put on but 3-5 days isn't unusual.  I completely agree that this type of stringing is very likely caused by water saturated PVA in most cases, however, I'm encountering this stringing right at the very beginning of each print, with filament that I have confirmed to be dehydrated (see attached image for confirmation of 15% Rh.

 

I will absolutely still try what you suggested just in case these sensors aren't as reliable as I assumed, but I wonder if there are any other print settings which could help reduce this stringing?

 

Thanks again for your help!

[gr5 2,173]

Are you putting your filament into something to keep it dry while at the same time printing?  I find that after a few hours on the back of my printer the filament needs drying again.  Once I put the filament in a zip lock bag on the table behind the printer with dessicant (think 1 cup/quarter liter dessicant) and with the ziplock bag unzipped just enough to let the filament out.  I haven't done that for years and I don't remember if that worked or not.

 

I tend to do 30 to 60 minute prints so don't have to worry about this too often.  There are companies that make dry boxes that go behind the printer so you the filament is only exposed for a few minutes on it's way from the drybox to the bowden.

 

[jcrscott 0]

Thanks again for the reply gr5, I keep my filament (support and base material) in a Sunlu filament drier set to 50C while printing.  With other filaments and support materials this has helped mitigate a lot of other printing issues I was having separate from stringing.

 

I've had a moderate amount of success by changing the follow print settings for the Gizmodorks PVA on my most recent print:

1) "Retraction Distance" increased to 6.5mm 

2) "Maximum Retraction Count" set to 9999 (ensuring retraction always happens)

3) "Minimum Extrusion Distance Window" set equal to "Retraction Distance" at 6.5mm

4) Disable "Limit Support Retractions"

5) "Support Wall Line Count" increased to 2

 

The following settings changes also seem to have resolved support interface errors:

1) "Gradual Support Infill Steps" increased to 5

2) "Gradual Support Infill Step Height" increased to 1.5mm

3) "Support Density" = 100%

4) "Support Roof Thickness" increased to 1.0mm

5) "Support Floor Thickness" increased to 1.0mm

6) "Support Interface Density" increased to 100%

7) "Small Hole Max Size" = 15mm

 

I've attached an image of the print with the updated settings.

 

[gr5 2,173]

Nothing strikes me as obvious.  Was there no retraction for the PVA before?

 

I'm looking at my default PVA settings and I see that the PVA only has 4.5mm retraction (default value) but the other material (nylon in my case right now) has 8mm retraction.  I didn't touch those values.  Maybe it's because nylon is so flexible and squishes a bit while printing so you need to retract more and PVA is stiffer?

 

Anyway I didn't get much stringing at all on my last print.  Maybe the gizmodorks PVA is much more flexible?

 

I really don't know what it is that you changed that might have helped things.  My print from yesterday where the PVA was nice and dry.  If I don't dry the PVA I get lots of stringing just like you.

 

 

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