I have read somewhere (can’t find it anymore) the nozzle switch retraction should be about 16mm. At least the length of the heatbreak (?). Most of the time the clogging ain’t happening at the moment of a nozzle switch. But I will give it a try with 1mm.
My last example wasn’t a print with a nozzle switch. The clogging happened at the moment the support started touching the model. That happened more than once at the exact same spot.
Last night I started a print, this morning I found out it didn’t even started. Was clogged right at the start. With a manual push on the filament I managed to start it this morning. It doesn’t feel like really stuck in the nozzle, a little downward push is enough to get the filament loading.
As said I have tested with a smaller retraction distance. I have tested with 1mm and 2mm. Both of the tests had clogged nozzles (left and right).
When resuming after clogging I can manually help the filament reloading. With a little bit of power the filament starts flowing. To me it looks like the extruder doesn’t have enough strength to push the filament down. Really clogged is not the case as I can see it.
@Rwide No, the example of the one colour print is printed with support from the same extruder (printed in copy mode). See this picture (not sharp, screenshot from video):
Less retraction means less heat creep based clogging. You should not be using/testing any values above 1 mm for any retractions at this point.
Sounds like heat creep based clogging to me.
It can usually be fixed by:
Making sure retractions are low.
Ensuring cooling block fan works.
Ensuring there is sufficient cooling paste on the heat break.
There is also a quick and dirty fix: Use a filament oiler with canola/rapeseed oil. This is what I did on the old sucky hotends. After that I had no issues with them.
Yes. The maximum recommended retraction for the J1 is 2mm. The dual extruder recommendation you showed may be for the other snapmaker printers that don’t have plugs to park on.
That does also mean not many have experimented with more, but 16mm seems would make clogs worse.
The new start gcode you added would also only help with jams in the first layer, maybe two. Not with soft skips far into the print.
I’m sort of out of ideas. Other options would be,
Some suggest new Bondtech extruder gears have sharper teeth that bite better. I’m dubious about that though.
Nuclear option: You can disable filament runout detection by extruder under Settings->Machine Settings. This means it also won’t catch real jams or runout though.
I sometimes wonder if the detection is just slightly too sensitive. The firmware could be edited to not trip so easily. That would take a lot of testing to get right though.
As mentioned earlier I have tested with Nozzle switch retractions from 1mm, 2mm and 16mm. All of them not succesfull. Yesterday I tested again to determine which retraction setting would be worse.
The left extruder did 16mm retraction, the right extruder 1mm. I started my two-colour, one-hour print. This print went without problems, surprising. I assumed I was lucky for once, so I started a second print with the same settings (left 16mm, right 1mm). Again completed without problems. I don’t understand it.
I won’t to try the cooling paste solution. Where and how do I apply which cooling paste?
For the thermal paste, it would be on the threads of the heatbreak. However, I’m not sure that’s necessary if using the Snapmaker all-metal hotends. Or even how/if the heatbreak is still threaded. (I haven’t disassembled the new hotend and don’t know if anyone has tried. The nozzle cannot be changed on it.)
On old hotends you would add a little thermal paste on the heatbreak threads. I used some Noctua cpu thermal paste. I didn’t find it made any significant difference though (if that’s all you do).
Tested again the two-coloured print. This time both extruders 1mm nozzle switch retraction and 0.8mm normal retraction. Clogged again at both extruders. The first clogging happened a few layers after the second extruder came in (the first 40% is only the left extruder). Maybe is has something to do with the temperatures while switching the extruders?
Although the standby temperature is 175C the extruder that is not in use remains most of the time 195C. Why doesn’t it drop tot 175C? Is 195C to warm?
@Michiel I don’t really understand why you keep testing different retraction lengths when you have clogging issues. Just minimize all the factors that can lead to clogging and see what happends.
As far as the temps go, you’re right. PLA degrades faster at higher temps. So lowering the standby temp is a good idea. PLA + Heat + Moisture = Faster Degradation. I would lower the standby temp to 50 if I were you. Then you can raise it to a reasonable temp level once you are free of the clogging issues.
PLA’s softening temp is 50C, but it doesn’t liquify/melt until 150C+. Cooling all the way to 50C for every filament change isn’t likely to help, and likely to make prints take eons.
Being warm may spoil the flow for a few mm’s, but this is what the wipe tower takes care of.
Maybe I’m just nuts, but again… I stopped cooling at all during prints that don’t have long pauses (change tools on nearly every layer) and it has no trouble.
Certainly running the steel nozzles, one needs to bump up the temp vs brass to get proper extrusion since it doesn’t conduct heat as well.
@Wombley Yes but this is troubleshooting and he could do it once to see if it helps.
Heat creep related clogs expand the filament inside the heatbreak. Because the filament is soft, it can function like a cork inside the heatbreak. This cork effect usually releases after a cooldown/heat up cycle.
I do agree that increasing the print temp is a good idea though.
I have done some testing again and came at a point the two test models went right (almost) every time. All retractions at 0.8mm, temperatures 210C, build plate 50C, 200mm/s, Z seams random (I have no clue whether this would have a positive effect, but I changed it right before it went right for the first time).
The first time with the top lid off, later closed it. Both went right.
I don’t know what the real trick was, but I looks fine right now.
