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Cura 3.2.1, Dual extruder 2-to-1 hot-end Problems

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I'm new to 3D Printing and I have a Zonestar Z8XM2 printer.

It's a decent machine after a few upgrades (like belt tensioners and spool holders) and has a Chinese made complete-knockoff cyclops 2-to-1 hot-end.

They didn't even copy the cyclops from their drawings, they basically designed their own so parts are not interchangeable.

Whatever... it works. If I have problems, I'll worry about it then.


I've been able to get good single color prints and I'm happy with the cheap printer after the modifications.

It's capable of color mixing, but I haven't even started down that path yet...

I've done many single color prints successfully and now a print with 2 different parts, each their own color, but I noticed an issue with the color ending up in the other part when it shouldn't.

Now I know my 'Prime Tower Minimum Volume' was set FAR too small and didn't extrude all of the previous color out before switching colors.

Luckily the color was on the inside walls and isn't noticeable when assembled.


What I'm working on now is a single part with 2 colors.

The problem that I'm having is when Cura starts a new layer, it's jumping from color 2 immediately to the color 1 without using up all of color 2 first or using the prime tower.

For the first layer, it appears to work correctly, it will extrude color 1, go use the prime tower with color 2 thus getting the rest of color 1 out, then uses color 2 on the print.

Now, when it moves to the 2nd layer, it immediately switches from color 2 to color 1 and starts printing without getting the rest of color 2 out first.

So obviously whats going to happen is the first however many lines of the 2nd layer comes out as color 2, then will fade to color 1 and will finish up color 1 as it should for that layer.

Then it continues on as it did with the first layer and uses the prime tower between color changes and color 2 will look fine.

Color 1 will have color 2 mixed in until it empties out color 1 from the hot-end.

To me, Cura is basically missing the prime tower when moving to a new layer.

Now, all of this is within the Cura layer view simulator. I have not printed the part yet as I can tell it's already going to have problems...


Since I'm new to all of this, am I missing something in Cura?

I'm using the prime tower set at 16mm 'Prime Tower Size' and 50mm cubed 'Prime Tower Minimum Volume'. I honestly don't know if this is a large enough minimum volume, but we'll find out when I go to print. I'll just have to adjust that for my specific printer.

Is there another setting that I need to change which will use the prime tower between every color change, not just the color changes during a layer?

Is Cura supposed to be alternating color 1, then color 2 for layer 1, then color 2, then 1 for layer 2? Basically alternating which color it starts with at each layer so it only uses the prime tower 1 time per layer?


Is there a way to tell it how much volume is left in my hot-end and start using color 2 at the end of color 1's run? So when it finishes up color 1's area, it'll be basically ready to switch to color 2?

In reality, from playing with the filament, I've actually seen the color mix before changing, it's not an immediate color change. I expect I will never get away from a prime tower completely.


Any help is appreciated, thanks!


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