Dual Extruder Prime Tower Issue

I’m printing using two extruders to get two colors. My second color does not appear until layer 16. The prime tower does not print anything for extruder 2 in the prime tower until it reaches layer 16. Then of course it spews extruders 2 filament into thin air.

Should it not print each layer for the prime tower in each and every layer even if the model does not use the extruder for that layer.

The extruder will print to the prime tower when on the change of the toolhead. So once the Color1 is done for the layer, the Color2 will prime the nozzle (in case of ooze) by printing to the tower. Color2 will finish off the current layer, then continue printing its portion of the next layer. Color1 will then prime itself by printing to the tower and print its portion of the layer.

Proper dual color prints should have both colors on every layer (one color could be inside the object). It sounds like your object doesn’t comply with this. If that’s the case, you may want to adjust the gcode (through the slicer) to reduce the extruder temp that won’t be printing. Keeping the extruder at temp without extruding filament could lead to a clog (carbonization of filament).

Can you upload the two STLs of your object?

“Proper dual color prints should have both colors on every layer”

So your openly admitting that cura lulzbot edition is not capable of printing this…
because it’s not a “Proper dual color print” and your answer to printing this is to just move along to another slicer?

Wow!!! If you can’t get the programming right, change the rules. That’s a huge cop out.

This is probably a moot point now but as requested here are the stl’s for the model. This is actually part of a larger print/design but I cut it down to make it simpler. A previous version of this was printed by someone else on a prusa with the mmu option using prusa slic3r. I am including a pic of that print (which it aced by the way).
The “X-Contoller” is also printed in dual color and is just as white as the legend logo’s but looks grayish in the picture because of shadowing.
Base.stl (429 KB)
Legend.stl (318 KB)

I’m not sure where this comes from but I don’t believe it. Take a look at the 3DBenchy files for dual printing which I have sliced and printed multiple times with CuraLE (including 3.6.18).

The prime tower has something printed on every layer. When the second extruder is finally used, it prints on a prime tower built with the first extruder.

I also sliced the model posted in this thread with CuraLE 3.6.18 and the preview (in CuraLE and Craftware) looks correct to me.

The prime tower should have have layers 1-15 printed with the first color so that the second color on layer 16 gets put on top of them. Something is wrong with the slicing if the second color is printing into thin air.

Something is wrong indeed. If the layers prime on top of each other they would eventually get taller than the print due both colors being on same layer and the tower height effectively doubling on that layer.

They definitely print as two walls on the prime tower and as far as i can remember, always have.

Load my two stl’s and merge. Pick materials that show up with different colors in preview. Then pull down to layer 1 and begin to go up.

That being said. I thought this forum was used or monitored by the actual developers? I was attempting to report a bug. If not can anyone tell me where bugs should be reported?

Okay. Maybe the “proper dual color prints should have both colors on every layer” is a blanket statement. My apologies.

I’ve printed that cone before and had no problems. Most likely didn’t use Cura. But I’m sure with some tweaking of the dual extrusion profile you can do it with Cura.

I don’t know where you’re coming off that I said to switch slicers. I used S3D with my previous printer, so since it was paid for it continued on to my Taz5. Relax… not worth getting your panties wadded up. There are plenty of slicers out there. Cura is pretty good in my book, and, TBH, LE put a lot of effort into features.

You’re right, it was a bad blanket statement on my part about the “proper dual color prints should have both colors on every layer”.

The prime tower has something printed on every layer. When the second extruder is finally used, it prints on a prime tower built with the first extruder.

Yes, I believe that’s correct. Filament is deposited on the prime tower at the beginning of each layer.


From what I’ve seen, slicers are smart enough to schedule the extrusions so that only one color is deposited on the prime tower per layer. So ColorA starts Layer10, ColorB on the prime tower and finishes Layer10. ColorB then begins Layer11 (no prime tower), ColorA then prints a layer to the prime tower, and finishes Layer11. ColorA begins Layer12 (no prime tower)… etc.

Not sure how you formally report a bug with Cura… should be through the forums, but it seems like LB only spot checks.


Take 5 mins and load the STL’s, run the layers up. Use any two color print. You will find that it does NOT print one color on top of the other on the prime tower. It creates two walls. The ooze shield does appear to alternate colors on the same layer, but not the prime tower.

Work the layer slider up until the second color comes into play and you can clearly see it’s hanging in mid air. No need to actually print anything. It prints exactly the way the preview shows it and the preview shows it. Wait, I’ll attach a screen shot.

You can see in the 1st pic both the red outer wall and the white inner wall, but in pic 2 when the red (hotend1) is turned off you can see two gaps. It only prints it when the color appears on the layer. However in real life it does not suspend in mid air like that. In the 3rd pic you can see with hotend1 on and hotend2 off the red wall goes all the way up.

Have not tried this but if I did do the cones I wonder if both the red wall and the white wall would have gaps. Either way you can’t convince me this is expect and accepted behavior.

Ok, I downloaded the cones and the prime tower did the exact same thing. Outer (Red) wall of tower is printed every layer all the way up even if that layer had no Red. Inner (White) wall only printed if white was on that layer.

However, when playing around I accidentally clicked on support. Telling it to use the White as the support material the inner wall of the prime tower did in fact print every layer. So this is a work around, but the downside is your print gets support as well. In my case I do not need nor want support for the actual model, it prints cleanly without it. Having support actually makes the cleanup harder, where as in my case no cleanup as all was or should be needed.

But at least for now it should actually wipe extruder2. They layers preview indicates it does.

Ok, this is a little off topic, but…

S3D=Simplify 3d correct? If so is it worth it. I’ve been thinking about buying it but there is no trial. Also I always liked that lulzbot had print profiles they had supposedly been tweaked. Problem is they seem to drop support for previous tool heads and machines so they are becoming less and less important, unless I keep shelling out for new tool heads. I had just bought a v2 dual six months before v3 came out. Now lots of filament profiles don’t appear if I say v2 and taz5. If I say v2 and taz6 and they are there. If I say v3 and taz5 and they are there. v2 and taz5, nope not there. I understand no longer making any changes and/or not having new filaments, but I don’t understand why they simply remove profiles altogether based on the tool head/machine combinations when the same combination had them in an earlier version.

Just because I upgrade to the lastest Cura LE should not mean I just rendered all my Taz 5 and older supported tool heads irrelevant. That and the fact they no longer offer parts for older tool heads; and in some cases even for current tool heads, is starting to make me think a TAZ (luzbot) is not what it once was. Seems like they are coming in 3rd and 4th in a lot of reviews the last few years. When I bought it they were always 1st or second and were leading the industry. Not so much any more. That guy named PRUSA seems to be doing that now.

Ok, stepping off my soapbox now.

I wasn’t careful enough with my analysis of CuraLE 3.7.18. The prime tower does, in fact, print each color in a separate X,Y location so it does indeed print color 2 in thin air (move the “camera” view to top down). This is obviously a bug and I’m not sure when it was introduced as I have successfully printed dual colors in previous versions of CuraLE. I need to do more research and then I will submit a bug report. I’m not sure if the process for submitting a bug report is documented anywhere (it should be) but I’m willing to bet that an email to support@lulzbot.com will be an adequate substitute.

FWIW, Ultimaker Cura 4.2.1 appears to have the same problem. Simplify 3D (S3D) does not have this issue. You asked if S3D is worth the money and my answer would be yes in this case as it does the prime tower correctly. There are some features in S3D I like better and some features in CuraLE I like better. I’d say that 90% (or more) of my printing has been sliced with CuraLE. For LulzBot printers, S3D will require some tinkering (and more tinkering if you use OctoPrint).

I like to experiment and have found that having multiple slicers in my toolbox can sometimes allow me to match a slicer feature to a model and get a better print.

There are other slicers (PrusaSlicer, KISSlicer, IceSL, Pathio) that might work but you will have to create a printer profile.

KISSlicer is free for a single extruder, but you have to pay for multiple extruder support.

IceSL and Pathio are both being developed and are currently beta releases. IceSL does not have support for the LulzBot TAZ6 Dual Extruder V3 yet. I submitted the LulzBot TAZ6 Single Extruder profile but the Dual Extruder is still a work in progress. Pathio has dual extruder support but I haven’t printed anything with my dual extruder yet.

This has been reported as a bug. See https://code.alephobjects.com/T9682 if you wish to follow its progress.