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Chronic Clogging in MicroSwiss Heat Break solved

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I was having chronic problems trying to print a retraction test with my Ender 3. I had recently replaced the stock extruder with a Micro Swiss all metal hot end. Being a bit "ham-fisted", I managed to break the thermistor soon after that. While changing that, I learned a bit (maybe not enough) about thermistortable11.h, calibrating thermistor profiles and configuring Marlin. Long story short, I got myself deeper and deeper into trouble until I could not print anything without clogging up the heat break by the time the printer started layer 2.

I found a useful thread on the same issue in another group and the mystery was solved.
Since I don't see a similar discussion here, I thought I would post the link: https://www.thingiverse.com/groups/i3/forums/general/topic:6463

Basically, one tradeoff of using the all-metal hot end is that retraction distances more than 4mm are likely to pull softened filament up into the cool end, the extruder may then "jam" the soft filament in the heat break, when it pushes back down.
I have still to investigate how much stringing this limitation is going to leave me dealing with, but at least restricting my retraction distance to 1.5mm in Cura has resolved that clogging problem.
BTW - The Cura 4.3.0 end G code for Ender 3 also retracts the filament at the end of a job. For some reason, two successive commands each retract by 2mm, for a total of 4mm. Hoping I don't regret it, I have removed one of those retractions, thinking the worst case will be when a print job ends with a retraction command, followed by the end Gcode retraction command(s).

You, sir, just solved my problem. Thank you!

I am very glad to hear that.
Just in case, I should add here that I also learned that if I turned off the printer before the hot end had cooled, heat creep sometimes caused filament in the heatbreak throat to soften and stick in there. I have more than once had to use a small drill bit to clean out a clog formed that way...

micro all metal 3mm retract @40mm works great for me
load /unload allways 210 & push in before pulling out
cura 4.4 & genuine bmg/ bowden ender5

also use 3mm on the micro swiss 300 cr10 with red alloy extruder setup.... just a though you do have a genuine one and not a clone ? a way of telling is if you have holes for the heat block in the top block/part ...Only a thought but there's plenty nocking about and i fell into that trap a while back it had been reboxed the cheeky ebay seller

I did order and pay for a genuine Micro Swiss all-metal hot end, from a reputable online store.
It does have 3mm screw holes in the finned body, but no screws are installed.
The top end is a plastic collet, not a pneumatic connector.
Came in the right box and looks like the ones on their website.

The problem is that 1.5mm retraction is too little for a bowden printer. The conversation you linked is from a Wanhao Duplicator group which is a direct drive printer.

I also got a micro swiss some months ago, and after some time I found out that going back to a brass nozzle instead of the steel one included in the kit helps with stringing. I also couldn't keep the previous retraction settings of 5mm (tried a benchy and clogged the hotend after 30 mins), I'm now running 3.5mm at 30mm/s speed and I've pretty much solved the stringing problems. Also disregard the micro swiss suggestion of raising the temperatures, 200 is fine.

Thank you, yes I understand the Wanhao has a different configuration, but some of their comments also helped me understand my problem.
I recently converted my setup to direct drive, but only reduced the retraction distance to 6mm and knew nothing about the end gcode in Cura.
I used 8 mm at 25mm/sec, when I had the stock Bowden configuration, and still got stringing. (Most of my PLA got wet, after being open for a few months, and it took me a while to realize that was my main problem.)
My first 15hr print with brand new PLA and 1.5mm retraction is beautiful (no gaps, no zits, no layer issues) but when I came to retract the filament the next morning, it was stuck in the nozzle. Heating to 220 and extruding a few mm first eventually broke it free.
I am wondering now whether I should let Cura retract 4mm or 0mm at the end of a job. I presently have that set to 2 mm, thinking Cura may add that to one final 1.5mm retraction at the end of a job.

What's your retraction speed out of curiosity?

I am presently printing using the Cura 4.3.0, Standard Quality (0.20mm) profile, except that I have lowered the retraction distance to 1.5mm and the retraction speed is 45mm/sec.

Hi, that is a long thread (didn't read it), but regarding the 4mm retraction, I recall a similar discussion for cr10's, and folks (with microswiss hot ends) noted they were using >4mm with success, but nothing that seemed crazy. I use 5.2mm @ 45mm/s with my CR10 S Pro with a Micro Swiss, and have had zero issues (that I can recall). 4mm was too low for many of the filaments I have tried, so I had to go higher. The 4mm suggestion / warning was in a manufacturer produced setup video on yt for my hot end as well (CR10S Pro). Some people will also recommend an oiler to help with chronic clogging, but I have no experience with those - just mentioning it if things get out of hand and you have no better option. I'd suggest checking the hot end cooling fan just in case.

Excessive retractions in the end gcode have caused me problems in the past with my Ender3, it was evident in my case when there was a perfect print on the bed and the next one couldn't start due to the clog. My start gcode does a purge line so anything that oozes from the nozzle is not an issue anyway.

Something else that occurred to me since your printer had issues early in the print - it sounds like a problem I had when the nozzle was too low for the first layer. I had problems like what you described when the nozzle z offset was not high enough to allow the correct amount of filament to come out, or my bed was not level and one side of the first layer was fine and the other was almost non-existent. The nozzle was effectively capped off for part of most of the first layer which I think compounded the retractions in that layer causing the clogs.

What was the retraction value you were using prior, that was causing problems?

Thanks for sharing your settings. That is why I posted here. Hoping the discussion helps others.
I forgot to mention in the original post that I recently converted to “direct drive” by mounting the extruder motor onto a bracket fixed to the extruder carriage. (https://www.thingiverse.com/make:718679, printed in carbon-fibre filled PLA, with some additional stiffening.)
My Bowden tube is now about 20mm long, between the metal extruder cold end and the Micro Swiss input.
I was using 6mm retraction at 25 mm/sec with this configuration but having clogging issues with the hot end, with brand new PLA filament. While printing at 205degC, I could hear a graunching sound from the extruder which eventually stopped extruding in mid-print. Evidentially, that sound is one of the clues.

Ah cool, I saw your reply also above, and that makes more sense for using 1.5mm retraction :D. As another datapoint, my Ender3 uses a Titan Aero and I use 0.5 to 0.8mm @ 35mm/s. It sometimes clogs but only with the last bit of MakerGeeks PLA+ which I have left, it has no problems with any other PLA or PLA+ I throw at it, and PETG also seems to work well with that setup. I used 0.8mm with PETG which is at the higher end of the range for retraction.

I typically print around 207-218C with PLA on my Ender3 (Titan Aero) and CR10S Pro (MicroSwiss). I can print lower, but feel like the prints are a bit stronger when I run them a few degrees hotter. If you find that there are still problems with clogging at 205, then I would suggest checking that the cooling duct is not pointed too high - pointed at the nozzle, which I think has caused me some problems in the past before I swapped the duct out. Using the silicone sock on the hot end block is aslo a good idea if you have one. Good luck!