TAZ 6 PLA + PVA Dual Extrusion Problems

Hello,

I am using a Lulzbot TAZ 6 at work for some prototyping, and we have chosen to use PLA + PVA so that we can build support materials and easily pull off/dissolve our supports, but this has been coming with a litany of problems. For some reason both filaments are starting to have problems extruding. I have successfully printed sample models in each filament with none of these problems, but when I go to do dual printing with all the settings the same, I’m seeing serious problems.

For the PLA, I am seeing the drive gear tearing into and eating away the filament, thus not actually allowing it to extrude or retract. This can happen multiple times in a print, and consistently so. I have also seen this happen to our reel of ABS, but found out that it occurred because the filament got caught and couldn’t un-ravel at all. I know the nozzle is clean (cleaned it twice), temperature is adequate (215C), and I even turned of retraction. My fear is that the stress of actually feeding the filament is somehow causing the drive gear to instead tear apart the filament instead of driving it to the hot end to be extruded.

The PVA is another story. This stuff isn’t really fun to work with to begin with so it is pretty frustrating in general. Regardless of my views on it as a material, it seems to be struggling to extrude as well. Again, the extruder was clean, temperature is adequate (190C), and no retraction. The filament in this case though doesn’t get ground off until it pig-tails and jams between the drive gear and the hot end. This happened multiple times and mysteriously vanished. I think the only setting I changed was the print speed in Cura, but that doesn’t seem to have that much effect, so I’m wondering what exactly was causing this.

Does anyone have any tips/thoughts on what may be happening?

I’ve been thinking of printing an alternate spool holder like this one: http://www.thingiverse.com/thing:725128. If my suspicion about the stress of feeding the filament is correct, I think that this may be a possible solution.

I will try to attach pictures of what I’m seeing, but this forum setup keeps rejecting when I add attachments…

Any thoughts/help would be greatly appreciated.

Pictures are attached.


Try increasing the extrusion temp a bit (2 to 5C) and give the idler screws a half turn (all four).

Have you printed any other filaments in the nozzles? Maybe they need a good purge of old material.

As of now, the PVA is extruding fine with no problems, but the PLA is still tearing up and getting filament dust inside the print head that I constantly need to clean out.

I previously increased the temperature up - the PLA was printing well at 205C, but I bumped it up to 215C; the PVA was printing well at 180C, and I bumped it to 190C - but that still had the same effect. I also purged out all the ABS that was previously in the nozzle for the PLA. PVA is the only material we’ve used in the second nozzle.

I’m still stuck on the thought that it is those awkward loopy filament feeder tubes and the effort that is required to pull the filament in is too great for the drive gear, so it just decides to tear the filament. The PLA is also very stiff and wants to maintain it’s original loops from the reel, so that also pulls me towards that theory. I’m thinking I’m going to try and purge the PLA out, and print a new spool holder in ABS (which has been working well) and see if that mitigates the side effects I’ve been seeing on the PLA.

Well, I use top mounted spool holders currently on my Dual extruder Taz 6, and maybe that would help your issue also. I did not use them for your reason/s, but just like them better than the side mount. :wink:

It’s a good bet that you are experiencing the problem with heat creep that others have had.

https://forum.lulzbot.com/t/adjustable-heat-bed-glass-mount/38/1

With low temperature plastics like PLA, the heat from the hot end gets conducted up the feeder system and, after a while, softens the filament at the hobbed bolt that feeds the extruder. The hobbed bolt then chews up the filament until it can’t feed any more. That’s why you’re seeing filament dust. Unfortunately, the little blower fans included with the dual extruder just don’t move enough air to cool the heat sink and prevent that heat conductance.

For higher temperature plastics, not a problem because not enough heat gets past the heat sink to soften and cause this issue. You are probably seeing the start of the print working really well, then after an hour or so it starts to degrade as the feeder starts to slip.

First post for me here .

I have been using Taz machines for the past couple of years and at the present command an fleet of eight Taz 6’s.

I can speak to the problem you having feeding PLA. The method used to feed filament on the Taz is flawed. The combination of three things causes more resistance than the hobbed bolt can pull.

Firstly, the change of direction, filament is pulled off the reel rearward, turns upward, forward and then downward as it is fed into the extruder, combined with the “memory” that the filament has from being spooled, this causes friction inside the tube.

Next, the tube itself. Either the diameter is too small, or the material is too “grippy” (mainly observed with PLA), again causing friction.

Last, the weight of the spool (as is wishes to exercise some Newtonian physics and resist rotation) on the provided, rectangular-ly profiled filament mount, in conjunction with overlaps of filament wrapped around the spool that result from re-winding the filament that may have previously unraveled.

The long and short of this problem is that you will likely see great improvement by deleting the tube and moving to a top mounted filament system. There are several good designs available for print. I’ve moved my current machines to top mount, and previous machines as well. All of the printers experienced the same issues of the hobbed bolt gnawing a “rut” into the PLA and stopping extrusion.

Sometimes it’s good to know you’re not alone.

Did you ever sort out the PVA issues? I found this thread in my searches prior to attempting my first PVA support print. It’s been my experience that I tend to experience all the same first time issues trying anything new that the users here have. Thanks in advance for any insight.

Sorry, late to the party, but this may be useful.

With the PLA, I’m pretty sure you are experiencing heat creep. Here’s how I fixed it 100% on my Taz5 with a dual extruder:

https://forum.lulzbot.com/t/dual-extruder-v2-heat-block-fan-upgrade/3366/1

With regard to the PVA curling up between the extruder and the drive bolt, that has happened to me when the PVA extruder head is too close to the build plate. Anything that increases back pressure can cause curling of softer filaments like PVA. When I align my head height, I use a larger gap for the PVA head height.

Hope this helps.