Dual Extrusion Head: Heat creep? More likely: Bad feeder!

Hi folks,
on facebook (and I seem to remember here also) there are a few users assuming that they suffer from heat creep, some (here a picture stolen from Facebook user Nand Maas) going to extreme measures:

I honestly doubt it. On the one hand, even the shown picture did not yield success, and, on the other hand, the general construction of the hotend does strike me as rather sound, better even than the single extruder head.

The problem people report is nozzle clogging, accompanied by a visible thickening of the filament they pull out from the hotend. I now had the same, but what set apart that failing print from other, successful ones, was a lot of retraction happening. So, my assumption now is, that the feeder A) grinds down the filament during the retract/reinsert process to an extent that the feeder cannot grab it anymore well enough, and/or B) the forces involved dislodge the feeder lever enough to it losing grip. The popping feeder levers several users reported would then just be the extreme variant of the same problem.

Problem is: My statistics is based on one failed print. I’d be curious: Those of you having problems - can you share the following observations:

  • Does the filament look grinded after a failure (stupid me did not look after my failure)?
  • Does it help to switch off retraction?
  • Does it help if you firmly wedge in the locking blocks Snapmaker published as a workaround for the popping feeder levers?

Guess this might be valuable information for both users and Snapmaker to get temporary or permanent solutions to the problem.

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And for those reading through this: the single extruder has the same issue, but the different design of the hot end in the SE and the fact that it is an SE has helped mask it. The DE does thousands more retractions than the SE due to the switching of filament throughout the print. Retraction is one of the first calibrations that should be done on both (following e-steps, which needs to be done first for retraction to be accurate).

Thank you for bringing this to light @Hauke. It seems so very many users of either one have no idea about it or the massive affects it can have, and are so often misdiagnosed.

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Like you say it, it sounds like there’s a recommended procedure to calibrate retractions - if so, what is it?

And, for me still important to clarify, is if the feeder system of the DE has systematic issues. Even if admittedly the number of retractions in my failed print was high, it was still not excessive, and honestly I would not have expected problems. Based on experience from a different printer I usually restrict retractions to travels longer than 10 mm and limit the max number of retractions in short succession to 20. If even with such settings the feeder fails, I’d say it is a bit disappointing. I am curious what Snapmaker will come up with as a fix for the popping feeder levers - that might be indicative for others also.

However, a parameter I did not yet play with is retraction speed - perhaps slower retraction is a good idea. And, last admittance: I do not use Luban, but Cura. Supposedly Snapmaker has done their homework and good retraction settings are in the Luban profiles. I guess I’ll take a look…

Edit: Just had a look. Here’s the parameters from the generic Luban PLA profile:

        "retraction_enable": {
            "default_value": true
        },
        "retraction_amount": {
            "default_value": 1
        },
        "retraction_retract_speed": {
            "default_value": 35
        },
        "retraction_prime_speed": {
            "default_value": 35
        },
        "retraction_extra_prime_amount": {
            "default_value": 0
        },
        "retraction_hop_enabled": {
            "default_value": true
        },
        "speed_z_hop": {
            "default_value": 10
        },
        "retraction_hop_only_when_collides": {
            "default_value": true
        },
        "retraction_hop": {
            "default_value": 1
        },
        "retraction_hop_after_extruder_switch": {
            "default_value": true
        },
        "retraction_hop_after_extruder_switch_height": {
            "default_value": 1
        },
        "switch_extruder_retraction_amount": {
            "default_value": 16
        },
        "switch_extruder_retraction_speeds": {
            "default_value": 25
        },
        "switch_extruder_retraction_speed": {
            "default_value": 25
        },
        "switch_extruder_prime_speed": {
            "default_value": 25
        },
        "switch_extruder_extra_prime_amount": {
            "default_value": 1
        },

I too primarily use Cura because I like having it’s plugin features and more control over my print settings. I have never heard or read about a specifically recommended procedure for calibrating retraction, but I just run a retraction tower a couple of times, with one changing only retraction speed, and the other changing only retraction distance, and choosing the two that give me the best print quality. For my Single Extruder, I found 1mm@10mm/s to be best for PLA, while PETG was best with 2mm@50mm/s. Luban’s defaults for the SE are 5mm@60mm/s for both, which is WAY too high for a direct drive extruder, and a common cause of the hot end clogs on the SE, as well as stringing in the prints.

Without knowing much about coding, looking at what you posted, I have to wonder why the “retraction amount” is 1, but then the “switch extruder retraction amount” is 16. Certainly sounds odd. Either way, as you mentioned, the immense number of retractions from both just printing and the switching of extruder sides is going to cause a LOT of grinding on the filament, and a high retraction amount sucking hot filament into a cold zone of the hot end is definitely going to make it prone to clogs.

There very well could be a production mechanical or software issue that was overlooked in their rush to get the product to market (seems to happen a lot these days with almost every company), and systematic troubleshooting to eliminate possibilities is definitely the way to go.

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DEFilamentCalibration01.stl (8.5 KB)
DEFilamentCalibration02.stl (8.3 KB)

These two parts are a model that I used to calibrate many retractions in a small amount of time. It helped me get very clean travels and minimal blobs and stringing. Though I’m still having the same issue of incorrect retraction issues somewhere, because during large prints, a nozzle will stop extruding because of expanded filament inside one of the nozzles.

I’ve attempted to lower retraction values to the low side, and have my average retraction setting at about 2.5 mm, while the nozzle switch retraction amount is set to something a bit higher, at 10. I’m assuming you want the nozzle switch retraction distance to be a bit higher in order to prevent oozing, but perhaps that is also what is causing the filament to clog up in the nozzle?


The issue is somewhat random in terms of when it happens. I can print the same 15 minute calibration 3 times just fine. Then the next one printed will clog a nozzle and prevent it from printing properly. It always leads to the same issue of an expanded, hardened tip of filament, along with a nice grind against the strand of filament further up. I set my standby temp to a very low value (75 celcius) Based on a suggestion on another user on these forums. Not sure if that has helped yet.

The question is: What’s the cause, what’s the result? Is it that the filament expands/gets stuck and then the feeder starts grinding, or is it the other way round: The feeder loses grip and the filament then builds up?

That said: 75°C sounds very cold to me, like filament getting hard at this temperature. This certainly will reduce oozing, but you’ll need to make sure that the printing only resumes after the nozzle is properly hot again.

That is the very question that I am asking myself at this point. I have believed it to be that the clog happens first, and then the grinding happens. I haven’t considered it to be the other way around. I’ll have to play around with that idea.

I thought 75C sounded very cold as well, but I took the advice as I am new to dual extruding, and thought it might help. I can confirm that the nozzle does wait until it is properly heated up for each switch. It also seems to keep different temperatures as the standby temp depending on how long the chosen nozzle will be inactive. I’m going to play around with that a bit higher and see if I get any better results. I have a good calibration model for short/rapid retractions and nozzle switches, but I need one that is able to test this specific issue.

Does anyone know of a calibration model that would be good for testing the nozzles for consistent extrusion when presented with variable active/inactive states between the nozzles? for example one area only having a small bit of text extruded from one nozzle while later on it is used for something larger, with more volume? Would something like that even help fix this I wonder… Still just trying to figure this dual extruding thing out.

It may have been heat creep after all - see in the new firmware:

…interesting I’d say…

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Very interesting. Here’s to the hope that this allows more wiggle room when it comes to making a working print profile for this DE! Updating later today!

Now I wonder if this was affecting the SE as well since they didn’t detail it.

Did a 5 hours print yesterday, kindof dual color: I had a thing with two parts, and against my habits printed both parts together, one in blue, one in black. Sliced in Cura, with the following retraction settings:
grafik
grafik
Still had a bit of oozing, but all in all prints came out fine, and no clogs or other hickups. Firmware 1.15.21, and the lever lock blockers in place.

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