I have managed to solve most of the problems with our Dual Extruder V3. Unfortunately it involved custom machined parts and the use of an $80k Markforged printer.
I made a new, much taller and far closer fitting heatsink to solve the heat soak problem. Then I reprinted the Dual Extruder frame using carbon fiber filament so I can use stronger springs, along with moving the filament spools to the top of the frame to reduce the chance of filament grinding. I redesigned the Y axis bearings with aluminum housing and ultra close fitting Delrin bushings, this mostly eliminated the table’s tendency to push down slightly when probing and wind up offsetting the head too far down. This also allowed better stability to check and adjust the extruders with a height gage I designed and printed.
I still have loads of problems with Cura, it loves to change settings around which is super annoying considering there are so many.
The purpose of this post is to show how poor this head (and frankly machine) is, it is pretty much unusable out of the box. I would like to go on an on with the many problems that remain with Cura but I think this post has gone on long enough.
I don’t think Lulzbot is to blame, the design came from E3D. If you have the capabilities to design and make your own heat sink why wouldn’t you split it in two? Seems to me that the shared heat sink for the two heads is part of the problem.
If you split the heatsink you would have to add some kind of machined frame behind it that now has to precisely align the now separate hot ends in multiple degrees of freedom. I think it would add a lot more complexity and weight. A tall heatsink is more effective as it allows the air more time in it to pick up and carry away more heat.
another pic below, could only upload 1 for some reason in op
Or I can fix their junk and run the PVA I need to use to make these… Ran out of filament last night and still didn’t have heat creep problems with PVA.
Oh wait… you’re printing with PVA and having clogging? You may not be having a heat-creep issue – this is a well known issue of PVA.
If PVA is heated above 200°C and held there it will go through a reaction that causes it to harden. This is non-reversible and heating it higher will not soften it again. So the trick is to only let it be above 200°C when you are actively extruding and drop the nozzle to a safe standby temperature when it isn’t actively extruding (e.g. when printing with the other nozzle). If it does harden, it usually means having to take apart the nozzle to try to clear it (heating wont do the trick).
When I use PVA, my profile prints it at 220°C but only while it is actively extruding. As soon as the nozzle is done it drops to a standby temp of only 170°C.
Cura automatically manages the temperature changes. As the non-PVA nozzle is getting near the end of the layer the g-code Cura produces will start heating the PVA nozzle so that it’s ready to print just about the time the non-PVA nozzle finishes.
I also use a purge tower and purge out a higher-than-normal amount of PVA filament just to get the stuff that has been sitting in the warm nozzle out and get to the fresh stuff before I start laying down filament. (I find the first bits that come out will sometimes show signs of starting to go bad. This stuff really does not like to sit around in a hot-nozzle that isn’t actively extruding.)
The larger heatsink idea is interesting… might be worthwhile experimenting with stacking an additional heatsink (drill holes for airflow) or changing for taller fins.
Most (if not all) my prints are ABS, so I haven’t had those issues with the Dual V3. Other than getting used to the filament loading and unloading, its been a pretty good toolhead.
Had clogging and grinding with the stock head, no more. I used (and still use) the default settings for Polymaker S1 PVA, I think the standby temp is 175. PVA printing temps vary wildly, eSun is 200 and Matterhackers is 245! I had to take the whole head apart a couple times and clear out the heat break a few times, it would be completely full of PVA. Never had a problem with PLA.
I don’t believe anything is wrong with the current heatsink on the Dual Extruder V3 but I strongly believe there is a problem with the air flow. This Fan Duct on Thingiverse solved the problems I was having with PLA/PLA and PLA/PVA printing. The description of how it works was enlightening for me.
While I purchased a higher flow Noctua fan, I was able to carefully reroute the wires on the existing fan and with the improved air flow, I haven’t had any problems so the higher flow fan sits on the shelf (there are two choices for higher flow, NF-A4x10 and NF-A4x20).
I tried for a week to get the V3 to work with no reproducible success. It would throw a heater error (“Heating failed, the system stopped! Heater_ID: 1 - Printer halted. kill() called!”) at what appears to be random time points. However the temp as reported appeared fine so I guess there must be a thermistor or heater issue. I didn’t experience any heat creep issue although the heater fan flow was in the opposite direction so I had to reverse it so that the airflow was over the hotend. The fan wires were obviously re-soldered and loosely applied electrical tape (previous owner claims V3 purchased directly from Lulzbot). So after many hours of frustration I’m returning and giving up on Dual extrusions with the Taz 6…
