"Pitting" or holes on A1 Mini. (Problems to dry filament?)

Bambu Lab A1 Series Bambu Lab A1 mini
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I have some problems with my A1 Mini. All of my prints have little holes on them, you can see those on the pictures below.

My filament is dry! I dried it 24h in a Creality Space Pi with a small lid opener, so that the moisture can escape. I also weigh my filament before, after 12h and right after 24h. After 12h it lost all of its moisture and weight didnt change after 24h hours. Therefore the filament has to be dry.

Now, when I reduce temperature and reduce retraction length, my results improve. I saw a post of someone on reddit sawing that there a phenomen called “pitting” which is very similar to wet filament. He states that, if you have too much retraction combined with too fast retraction, your nozzle could potentialy suck in air, which leads to similar popping sounds and printing results. https://www.reddit.com/r/FixMyPrint/comments/xpvu09/diagnosing_stringing_vs_branching_vs_pitting/

Thats the next thing that I will test, but I am not optimistic. Bambu has finetuned standard profiles for their own filament and printers and I saw nobody on the internet ever having “pitting” problems with the A1 series or similar. It always was wet filament. I guess all in all those standard profiles works for “everyone”, but why not for me? The issue got worse over time, but when I look on my very first print, I can already notice small holes and “pits”.

I am in contact with bambu support and they told me to clean my extruder etc. When I opened my toolhead I noticed some kind of oil, which was just everywhere, also behind the heating element, which doesnt make sense to me, because there aren’t moving parts or any other function that this oil would have. So my guess is, that this kind of oil gets into my hotend and burns like water, which causes all my problems. Bambu Support told me, that this oil is normal and should not be removed. But I never saw some A1 users that have oil in their extruder, filament sensor etc. plus bambu theirself never stated something like “oil your extruder gears” on their wiki.

I also noticed, that those problems not always happen. Even on the same print, those of more or less. They are often after layer changes, which would lead to that retraction/ r speed combination and not the oil theory.

Here is a list with what I have done already:

-Change nozzle: Got a new one from bambu, didnt improve something at all.
-Unclogged all my own nozzles
-Used hardened steel nozzles
-Dried Filament: Stated above, its dry!
-Printed out of a drybox/dryer
-Cleaned extruder besides of that oil.
-Cleaned build plate
-Cleaned all fans
-Reset to factory defaults plus complete calibration (did it 3 times)
-Maintenance for x and y
-Reisntalled bambu studio
-calibrated filament using orca

IMG_0984
IMG_09841920Ă—1440 621 KB

IMG_0983
IMG_09831920Ă—1440 669 KB

As you can see, only one side has those pitts. I used PETG HF in that case, just to demonstrate. PLA Basic shows same problems.

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Apologies for this but that does not mean your filament is dry. The Space Pi is just another heater in a box with fancy controls. Using a lid opener helps, but makes the connection to ambient humidity stronger and ambient humidity can stall, stop, and even reverse filament drying.

That the weight didn’t change is typically taken as the end of drying but it can also happen when ambient humidity slows and stops drying.

I don’t know if your printing issues are caused by moisture or not but your description doesn’t give enough information to say for certain if your filament is wet or dry.

To have a better handle on if your filament is drying properly or not, you need to note the relative humidity in the filament drying chamber. If it was down around 20%, then you probably are close to “dry”. If the chamber humidity was 40% or higher, your filament isn’t really dry. Dryer, but not “dry”. In between it’s harder to say.

Maybe your assertions that the filament is dry are accurate but you really can’t make that claim based on the facts you state. All you know is to the accuracy of your scale the weight isn’t changing which could also be the drying was ineffective because of ambient humidity.

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On filament drying. I run my heater at 140C until humidity in the box is roughly <20%. I then allow 24 hours or more until the humidity in the box is <16%. This indicates all the moisture is gone from the filament. Don’t open the box to let moisture escape, as this lets ambient moisture in again. Buy some large desiccant packs. I use and recommend these.

Regarding maintenance, have you attempted tensioning the belts or even possibly releasing some tension on them? I don’t know about the A1 series, but on the X1/P1S, the belt runs underneath and can rub. If not corrected, this can cause stepper motor issues. Look for areas of tension or belt misalignment.

Another possibility is your extruder gears may have some amount of particulate matter on them. Cleaning these with some IPA and compressed air may help.

Regarding the nozzle’s hot end, it sounds like you have replaced the hot end nozzle assembly. Is that correct? If you have, attempt to do some cold pulls on the new nozzle.

You do not state if this has happened on other filament rolls. If it only happens on one roll, there may be surface contamination on the filament. There are many printable filament cleaners, I recommend them. Dust is your enemy.

Please feel free to ask any questions you may have. I have been 3d printing for several years, and run a small business doing so.

I can also send a parts list for you to build your own drying box. Mine cost <$50.00 USD to make and can dry 8 rolls of filament at once.

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Thanks for your answer. The humidity was at 14% after 1h of drying. I also put 3 fresh silica bags in there to help with drying the air inside the chamber. So even when the chamber cooled down after drying, humidity didnt rise at all.

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That’s pretty hot. What is your box made of? What heater are you using? Just curious.

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Ok, with that added then I believe your filament is “dry”. But putting silica gel in a filament dryer can cause problems if not very dry. You mention you put in fresh silica gel so are probably fine, but those that put silica gel in filament dryers when the silica gel isn’t fresh can actually add to the humidity in a filament dryer. (Not for you since you have that covered as well.)

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Sorry! I meant 140F!!

Its a regular old airtight storage tote that you can get at walmart.

I use a small 120 volt PTC heater with a PID controller and SS relay. The boz is lined on the inside qith double bubble insulation.

Works like a champ

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I wondered. Cool beans, sound good. If Ineeded it and I may be at some point, I have what’s needed. I have a few PTC heaters lying around. I just lack space.

Edit because I have a huge headache and this post made little sense.

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Thanks for your answer. I let the dryer do its thing for 1h before i put the spool in it and put 3 desicant bags in there. The chamber should be dry before i put the spool in. I could try to dry the filament again, but without the lid holder.

The A1 has sensors to check if belts have the correct tension. They seem normal to me

I clean my extruder gears once again with IPA

I did cold pulls with all the nozzles.

PLA Basic silver on the over hand printed absolutly flawless and looks amazing with standard profile. Probably the best printed thing qualitywise, but could be due the color, that the holes arent that visible.

I get the feeling that my filaments just won’t get dry. I dried anothert spool of PETG by elegoo for around 24h at 65C and prints look as bad as before drying. I used the max flowrate calibration model, to check that it isn’t the speed nor the retraction. I also used a filament dust cleaner and the filament was put into a drybox right after drying. It has to be wet filament or a faulty printer.

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Drying filament just by looking at the time will not work. I have the Creality Space Pi dryer myself but the built-in hygrometer is just useless as it stops at 15%RH which for some filaments and in some situations is just still too humid. You need a hygrometer which measures well below 10%RH and stop drying when it shows something around 7 or 8%RH. This way you can rule out wet filament as cause for printing problems and if they still persist start lookling at other factors like printing speed, printing temp etc.

I also removed the dessicant from the dryer as in my opinion it is completely useless for the drying process. It just heats up as well and starts drying itself evaporation water it has accumulated while the heater is switched off and the “normal” humid air inside is dried by it. Dessicant is only usefull if you print directly from the dryer and store your filament inside of it for a longer time.

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The hygrometer on mine shows a RH of 13%. Another hygrometer that put in there showed 10%, but that’s the it’s limit I guess.

I increased the drying temp from 60C to 70C and hope that it helps. I dried it for 24h at 60C and put it in there again for 8h at 70C and it lost one more gram again, although I dried it already.

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This is a very important point. When drying, there is a big initial spike in humidity that will get picked up by desiccant. As the dry continues and humidity falls, there will be humidity from both the filament and the desiccant to get out of the dryer.

The best way to have desiccant actually be effective in filament drying is to dry the air before it gets admitted to the dryer to purge out the moist air.

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at 140f /60c the dessicant should not be releasing it’s moisture. Silica dessicant will remove moisture up to 150F, and won’t release it until 212, when the moisture can effectively boil off. This is why it must be regenerated at higher temps.

Clay dessicant is ineffective above 50c. If you are using clay dessicant, swap to silica

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to add to my previous post, when i worked in a lab, we regenerated at 105C

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The extruder gears could be slightly lubricated. But not in such a way that there is a layer of grease or even liquid grease where the filament moves directly along. Of course, the filament must remain free of grease. If there is something there, I would remove it and see if there is too much grease in the extruder and remove the excess.

You may be printing too hot for the filament at the print speed you are using. This can create fine threads during printing but also spider webs. Simply try reducing the temperature further and see if the filament can still be printed and the problem improves. And check whether the filament is over-extruding. You may need to reduce the flow (e.g. to 0.90 to 0.94 instead of the normal 0.98).

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You’re actually incorrect. It is not a step function where water is released or not. What happens is on a continuum where equilibrium is trying to be established the whole temperature range.

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that’s only true if the dessicant is near it’s saturation point. Fresh dessicant has no issue absorbing at 60c

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Sorry, misread your post a bit. Here is a bit more quantified information.
Generally at 140F a fresh batch of silica gel will absorb 7 or 8 grams of H20 per 100 grams of gel.

This means that if you are not getting good drying results, you either have old silica or not enough. I really recommend buying large gun safe silica bags. They are generally 100 grams each. My large drybox has three of them.

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Not going to argue with you. You have some misconceptions here.

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Screenshot 2024-09-30 114747
Here is a graph showing the absorbtion ability per 100g vs temp.