I am new to 3D printing as of April 2018. This post is mainly for those interested in acquiring the Dual V3 who also have little experience with 3D printing. It includes my troubleshooting processes and general tips/gotchas. My intention in purchasing the Dual V3 was to print PLA + PVA (Polydissolve in my case). Let my 70+ hours of testing save you some time.
Bottomline: I would either wait for the Dual V4 or be willing to replace a fan on the Dual V3 to solve its heat creep issue. I have returned my Dual V3 after a month of attempts. However, know that plenty of people ARE having success with the V3.
Note that I had printed with the single head for a month with no real issues. I was super impressed with how well the Taz 6 with the single head worked out of the box. I went from the first sample print to being productive immediately. Unfortunately, I didnāt have the same out of the box success with the Dual V3. With a few tweaks to solve heat creep and easier loading of filament, I expect Lulzbotās Dual V4 will be solid.
We picked up a Dual V3 for our Taz 6 near end of May. I checked the serial number to ensure sure it wasnāt going to have the thermal runaway problems of the early shipments. See service bulletin: https://www.lulzbot.com/sites/default/files/Thermistor_Service_Bulletin_2.pdf
MY SETUP:
Dual V3
Taz 6
Cura: v3.2.21
Marlin Firmware v1.1.8.59
PLA + PVA
I started with Lulzbotās example āimpossible gearsā. The first attempt failed (I donāt recall why). The second attempt was successful. Both prints used eSunās PLA+ and Polymakerās Polydissovle S1. I had the PLA in Extruder 1 (E1 - left) and the Polydissolve in Extruder 2 (E2 - right).
Following that, I was unable to achieve a single successful print using PLA and PVA. The feeder wheel would grind away at the filament, and then had nothing to bite into to feed the filament. At the beginning, I thought I was having issues with the PVA burning and clogging the head preventing the filament from feeding, even though my temperatures were never above 220. I could push filament through manually so I knew it wasnāt clogged. Only PVA had been run in E2 at this point. It took around five cold pulls to achieve a clean head, including one using PLA. To avoid future burning of PVA, I thought Iād run lower temperatures. I moved to 210, 205, and then 190. I didnāt see any more buring. Still, the print attempts failed due to filament grinding issues, primarily E2 with the PVA. Every time I had a filament grinding issue, I would check to see if the nozzle was clogged by whether or not I could push filament through manually. This proved that clogging was not an issue, and therefore not causing the filament grind. I was trying to print a disc about 150mm in diameter. There would be quite a bit of time that one extruder head would be sitting at standby temperature (180) while the other head was printing. I thought perhaps when the extruder that was standing by is called to print, the filament wasnāt molten enough and it could be having difficulty getting started and that resistance could cause the filament grinding. (You can still push PLA or PVA through the head manually when head temp is at 180.) So I raised the Initial Temperature to that higher than the printing temperature, hoping the overshoot would solve any resistance issues. This did not solve the issue. User kcchen_00 says that the Dual V3 likes running hot so I went the opposite direction than my earlier tests and heated things up. The PVA shouldnāt burn at 220 and so I tried printing PLA at 230 and Polydissolve at 220. Still no luck, the filament grinding issue wouldnāt go away. (I didnāt see any burning of the PVA.)
At two different points in my testing I had baked the PVA in the oven at low temp (170F) for a few hours to remove any moisture it had absorbed, in case that was the issue with the initial burning I had seen.
Amidst tests, I did have a successful test using PLA in both E1 & E2.
In my tests I also disabled any retraction, though no matter what, there is always retraction on layer change (or at least when thereās a tower in the mix). In the end, retraction or not, thatās not the issue. Similarly, I reduced retraction, acceleration, jerk, and printing speeds. It didnāt help.
HEAT CREEP!
It took me a lot of forum reading, but I finally found a thread that led me to the topic āheat creepā. Heat creep causes the filament to get soft near the feeder. When the feeder gear turns, it just slips on the softened filament and chews away at it. THIS is what I had been fighting the whole time.
ABS + HIPS
Once I learned about heat creep, I figured I would try ABS and HIPS: filaments that require higher temperatures and therefore may be less prone to heat creep softening the filament.
E1:ABS E2:HIPS E2 failed perhaps a couple hours in due to heat creep (filament grind). Because most of the heat creep fails were with E2, and usually support material, I switched materials around: E1:HIPS E2:ABS. The 37 hour print finished without any heat creep failure! The HIPS and ABS didnāt adhere to each other, but that has nothing to do with the Dual V3.
PLA + PVA (again)
Given that success, I thought Iād go back and try PLA + PVA again, but switch which extruder head they were in. E1:PVA E2:PLA. E2 failed after the first layer or two due to heat creep. (Filament grind).
ABS + PVA
I had seen some people having success with ABS + PVA. So, I thought Iād give that a try. E1:PVA E2:ABS. The first 9 hour print was a success! After having spent the prior three weeks with nothing but failures with the PVA, this was encouraging.
I then tried to repeat the same 9 hour print but it failed. E1 clogged about half-way through. This was my first clogging issue with the Dual V3. In this case it looked like the PVA had burned. It was the first time after a fail I couldnāt āeasilyā push filament through the head by hand. After a couple cold pulls with PLA, it was back to good. However, at this point my return window had closed, it was time to give up and return the Dual V3.
CONCLUSION
Being new to 3D printing, it wasnāt until nearing the end of the return window that I learned that what I was facing was heat creep. I had spent at least 70 hours between scouring the forums and baby sitting prints and tweaking parameters in Cura, trying to get successful prints. In the end it became clear that tweaking parameters in Cura was completely unnecessary. For the most part, you should be able to use default profile settings for your filament of choice and have success. Fighting heat creep canāt be won by tweaking parameters. My take is that tweaking parameters is really more about getting cleaner prints, not about getting the printer to work.
If I still owned the Dual V3, Iād be replacing the heat sink fan with a higher flow rate fan to solve heat creep. I believe JoeBowler300 found success after replacing the fan with a higher flow rate (CFM) fan:
https://forum.lulzbot.com/t/adjustable-heat-bed-glass-mount/38/1
PRINT WITH SD CARD
Between people saying Cura or their computer crashes or sleeps mid-print, and not wanting to be tethered to the printer, I print solely with the SD card and never had an issue.
LOADING FILAMENT
Some people have mentioned problems loading filament.
https://forum.lulzbot.com/t/lulzbot-taz-dual-extruder-v3-tool-head/5547/6
I can agree with that it is difficult at first, but after some tips and practice, it wonāt take much effort. I like the filament to arc clockwise for E1 and counter clockwise for E2ā¦and cut a taper on the end of the filament, more easily done with a dedicated pair of dikes vs the provided pliers/cutters. Position such that the pointed tip is down (see pic, notably the black filament). With my idler arms set with the spacer tool while no filament is loaded, and even with an additional turn or two, I donāt have any problems loading filament when squeezing the idler arms. I can push it all the way down into the extruder head, though you could stop once you got past the feeder wheel and then turn the thumb wheel to finish pulling it in.
FIRMWARE GOTCHA:
Watch outā¦if you press pause on the LCD mid-print, it will resume at the correct layer as expected, but will shift in x and y by about 5mm each. You canāt recover a print after that. Stay away from the pause button! I made a post on this. https://forum.lulzbot.com/t/xy-shift-after-pause-change-filament-taz-6-dual-v3/5951/3
This only affects the Dual V3, not the single head.
Expect this to be fixed in the next firmware update.
CURA BUGGY:
Not All Project Settings Saved:
Beware that when you save a project in Cura, it doesnāt save all the settingsā¦OR it doesnāt recall all of the settings. Brim/Skirt is one of those bugs. Be sure to review your settings!
Change Colors at Wrong Layer:
You can tell Cura to āChange Colorā at a specific layer and it will inject the commands into the gcode. However, itās off by a couple layers. I specified Layer 40, and when printing, it paused at layer 38.
Hangs on Slicing:
Iāve had many occasions where CURA canāt finish slicing the file. It hangs trying to āPrepareā. I often adjusted layer height to get it to compile. Once, I had to switch to a similar profile.
Printing One at a Time:
If you have multiple objects to print on your bed, and they are small/shallow enough such that the head wonāt run into the other prints while printing, you can tell Cura to print one at a time, versus printing all at once layer by layer. Watch out, Cura will move your parts to where it believes there wonāt be any interference. Visually things looked great in Cura, but when it printed, one of my two parts was printed at the edge of bed, way off from where Cura visually said it was, and the brim was printed on the metal z-zero-ing disc which meant the nozzle was forced to rise over that disc. https://forum.lulzbot.com/t/print-sequence-one-at-a-time-cura-visual-misrepresentation/6016/1
RECOVER FAILED PRINTS
Learn how to recover a failed print, this can save you print time. Simply put, say your print fails at layer 32, you can hack your gcode by removing most all the commands prior to layer 32, save that file and then have the printer run it, and it will start at layer 32 and continue with your print. I did this about five times with success. I didnāt find any straightforward Lulzbot Taz 6 specific tutorials (video or writeup) on how to do this, but after some testing eventually figured it out. I know it would be helpful to make a separate post on how to do this, but I donāt want to spend the time, given the accumulated time Iāve put into testing and writing already. But hereās a gotcha - it IS necessary that the head runs through the auto-leveling routine first, it cant just resume printing at layer 32 cuz it can be off by a significant amount (Iāve seen 4mm). The auto-leveling routine moves the head from corner to corner, and therefore could collide with your existing print. If your print is not shallow enough, or in the way, you must start your print from scratch.
WHEEL MOTION INDICATORS
One thing I found helpful while troubleshooting was to put little pieces of tape on the thumb wheels so that it was easy to see which way the wheels were moving etc ( such as looking for retraction). To the Lulzbot team, it would cost more time to print, and would require a dual head printer to print them, but you could print bright green dots near the perimeter of the wheels. See the attached pic.
