Dual Extruder design / Dry box setups

Snapmaker 2.0
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This is a description of the issues you may have if you have an elaborate dry box, Bowden tube setup that worked with your old single extruder head and your having issues with your new dual extruder.

Problem: inconsistent nozzle heights and rough prints.

Setup
A350 with new dual extruder. Custom dry box. Typical type from thingiverse style with 4 rolls, directly into Bowden tubes. then down to the extruder through the enclosure.

What i have found.
The way new dual extruder switches what nozzle it uses. Is by raising the nozzle mechanically against a spring. You can watch this happen during the change and also by hand when its is cold you can push up on the nozzle / heat sink / extruder. and it will move up and down.

This means the only thing holding the nozzle down is a spring. The actuator lifts up against the spring to get the nozzle out of the way for the other color / nozzle.

Why is this a problem? well the extruder is also part of this assembly that moves up and down. And if you have a non efficient drag filled Bowden system. Well the extruder will climb the filament and raise the nozzle during the print. So the Z-offset can change while printing depending on the drag of your filament supply system. Basically the extruder gears are stronger then the spring holding the nozzle down.

So a warning to everyone out there that may have a setup like this. REDUCING DRAG is now VERY important to the system printing consistency as a whole. I donā€™t blame snapmaker for this wholly since any way to make the extruder fixed and the nozzle move up and down would take up allot more vertical room then the print head is right now (and its very large as is) But i think they could of designed a system much more robust so the spring was much harder to work against.

Personally my fix is in the works as i am working on designing a dual extruder drive system for each filament. this would be a drive unit up at the box that would sense tension on the filament and dispense a amount that is programed in. I have some ideas with loops and light curtain switches. but in a way this first drive would take all the load off the second drive in the head to pull the filament any distance through the Bowden tube.

I am trying to develop a 100% stand alone system. Snapmaker isnā€™t as friendly in the controller as others. So i donā€™t want to effect the machine as is.

So good luck and if anyone knows of a correct cura profile for the dual extruder i would love to see it.

4 Likes
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Iā€™m thinking this is the cause of the problem Iā€™m having with switching nozzles - first layer goes OK with both nozzles, but nozzle 2 then didnā€™t lift up when switching back to nozzle 1 for the next layer. At the time I thought it had to be related to the nozzle, and did put a post to that effect.

I have a home-built box that feeds through about a metre of Capricorn tube, and the calibrations printed fine (using the breakaway white). But the white filament Iā€™m using for other tests is pretty awful, very rough white PLA (I thought this was the ideal opportunity to use it up!)

I think what is happening is that it is pulling it through (though I am not getting the problem you are mentioning) but when the nozzle tries to move back to the travel position then it canā€™t push the filament back through the tube so the head doesnā€™t lift all the way.

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Your final hypothesis would be easy to test.

Cut a 12" piece of filament and load it directly into the head unit, no tubes.

Still have problem then not the issue,

I got my issues to be 99% solved by

1st: Changing over to a PTFE tube for 2.85mm Filament

2nd And changing over my spool system to be a bottom direct bearing system.

Good luck.

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Tested by manual feeding of filament to right extruder and it worked fine, so I agree that any friction in the feed to this extruder can cause problems with switching, retraction, and nozzle height while printing

1 Like
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Yes it is a sensitive system but you can get most of the kinks worked out of it.

The little wedge that is posted around here to lock the driver in place really helps also.

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The little wedge wonā€™t help in this case - the force required to pull/push the filament actually moves the second print nozzle. I think this is a design issue - the print head should move to the correct position and not rely on springs or anything else to hold in place, but thatā€™s done now (and letā€™s not start on keeping the induction sensor for levellingā€¦)

Iā€™m adopting the same approach as above - using a much larger diameter PTFE tube. Early trials are promising

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andyd

Not to be a that guy. But your quoting my fix / post :slight_smile:

Anyways the wedges help because this version of the print head have a design issue in the latching mechanism. You will start to have skips or even pop opens on some filaments.

Just print them and use them. They work great. But your choice. I can only reccomend.

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Yes - thatā€™s the fix I was referring to (sorry, thought that was implicit in ā€œas aboveā€) and thanks for that. Iā€™ve also swapped out the original dry box for some eSun filament boxes, for a range of reasons.

I found some slightly larger ID stuff on Amazon (5mm) which may bend a bit easier; it is also delivered a bit faster (a lot of stuff we see in Australia is ex-China, and freight from there is still a bit chaotic).
I decided 5mm ID was fine for non-Bowden use as I donā€™t care if there is slop inside the tube.

My fiddling with the little springy things that the block ā€œlocksā€ shows they are fairly tight, so I wonder whether there was some dodgy QC on these. Iā€™m open to printing them, but the dual extruder has plenty of other things to fix before I get round to that problem.

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yeah it may be I got a really early one. for sure my left drive unit loves to pop open.

The larger PTFE is a major help. I actually just have to ones they provided in the enclosure and the pass through. Then the new stuff from the box on top and connect it by sliding the provided PTFE tube just inside the larger stuff. I also drilled a hole on the top plexi so my box is on top and just tubes going down through the one pass through.

Australia yeah lots of different climate to deal with then Minnesota.

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Interesting, but why is it only a problem with the right extruder. They should be the same, or do they have different springs? And the calibration prints worksā€¦

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Well the right extruder has a greater movement with it. It is the one that retracts and extends for the nozzle change i believe.

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But why does the test calibration print work then?
I dont see full settings for retraction on the right head in luban.

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There are no ā€œsettingsā€ in luban for it that i know of.

In cura you can set;
Nozzle retract distance
Filimat retract distance.
Filimat retract speed.

As to why.
My issue was drag on the filimat. So the extruder would climb the filimat so slightly.

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I found the settings, I got it much better when increasing the prime settings. I think the problem is that the support filament is drawn back when the head is changed and more must be pushed out before printing.

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Iā€™m not aware that the test print does work (with the setup as specified by Snapmaker using Snapmaker provided newly unsealed PLA, and the instructions provided).

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Can you explain what prime settings youā€™re referring to? Are they in Luban?

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Prime

So retract and post retract prime in cura.
Not sure if luban has equivalents.

Snapmaker 2.0 default is like 14mm or something.

My calibrated retract is 1mm. The too much retract is the #1 suspect in the clogs and jam issues some are having.

1 Like
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I raised a bug for this - firmware is printing the left nozzle at 185Āŗ going on 200Āŗ where the breakaway filament provided should print at 220Āŗ.

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I hope they see it. Seems like reporting with Support Ticket Form
works better

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@Spaced,

Iā€™m having an issue where everything prints fine for a while and then after about .5" in height, something happens and the whole print separates from the bed and starts printing in mid air. I am now assuming that Iā€™m seeing what youā€™re talking about here.

On the PTFE, is the current extruder set up to accept 6mm OD tubing or do you just bring it close and call it a day? Also, do you have an enclosure? If so, you just remove the ā€œplugā€?