A1 Mini PETG - Bridging and stringing

[ThomasB]

Hi,

I’ve had my A1 Mini for a few weeks, and PLA and TPU, I’ve managed fine. Now, I’ve almost got my PETG to work as well, but there are some issues. After much trial and error, I rather ask here…

My filament is:
Brand: Clas Ohlson
Type: PETG (1,75 mm)
Series: Universal

Recommended temperature between 220-245 degrees Celcius

I’ve dried the filament in Sunlu Filadryer S2 twice for 6 hours each time at 50 degrees (default settings). It was getting way better after first dry, no change after the second.

Okey, my problem is:

• Stringing - not very bad after drying, but some stringing occur
• Bridging generally good, but some lines are just broken (see temp towers for “loose threads”).
• Filament sticking to nozzle (not very bad, but a bit, and it ends up on side surfaces of models - easy to remove, but still, artefacts…)
• Hard to print signs with small text or details (not too small, slicing ok), because if it starts with the lettering, the smallest one just gets dragged around, while bigger ones are better (maybe change the print order…)

I have been printing temperature towers for PETG, just to troubleshoot, and have landed on 255 degrees Celcius as the general best for my filament (based on those temp towers). I have also calibrated the flow dynamics, and use that result (0.045 K) during print instead of the auto flow calibration before each print.

Here are some pictures:

Above pictures shows my latest temperature tower print. I’ve just cut down to 260 and 255 degrees Celcius part to save on print time.

Retraction settings are Bambu slicer defaults for 0.4 mm nozzle, except for disabling of z-hop this time:

Retraction length: 0,8 mm
Z-hop: 0 (only changed parameter)
Retraction speed: 30 mm/s

Stringing is probably ok to many, but I wish it were nothing to clean up, like on my PLA prints. Not easy to spot on pictures, maybe, except for the stringiness before printing the model. (The model was removed from the textured PEI plate before I took the picture, but I left the “stringing-tale” attached to the model to show it).

Bridges at 260 not good enough, but 255 okey - except for that broken “tail”. It also occurs at all lower temperatures (have tested it, gets worse and worse for 250 and 245 etc). I have been watching during print, and the start of the bridges (defined as line type overhang wall in Bambu Slicer - blue) are printing perfect. It’s when it starts to fill in-between those (bridge in Bambu Slicer - light blue) that “tail” / “cut” of filament is occurring.

From Bambu Studio:

There’s also a small sagging line at the 255 degrees Celcius bridge - this has just started to happen - this temperature normally shows nice bridge except for that “tail”.

Here are pictures of earlier temperature tower with retraction set to 1.5 mm and z-hop at 0,8 mm:

Note the “lines” along the 35 degree overhang…

Pictures of first temp towers ever from PETG - before drying - of course very bad:

---

When trying to print the Bambu Cube (or V2 of it), it ends up like this:

Could have looked better…

Here’s how the first layers gets:

This type of stringing / dragging the filament around is very annoying, especially when trying to make round or shaped signs with text elements when faced down against the textured PEI plate to get rid of the print lines.

I wash the textured PEI plate with water and dish soap before prints. I have also tried to use alcohol stuff, and it works good - models really stick to it. However, that first thin line of the very start at first layer almost never start where the nozzle meet the bed for the start point. But then it’s nice.

I hope for some advice about what to try here…

PS! Is the A1 mini worse at PETG than P1S? I am planning to upgrade to P1S, but couldn’t wait to get started, so I try the A1 mini for a few months. Got the impression it should be okey.

[ThomasB]

I printed the Bambu Cube v2 again multiple times, but got that stringiness on the first layer(s), where the filament was dragged inside the circle / hole.

I tried lowering bed temperature from 80 to 70 C (as that is default for PETG), while print temperature remained at 255 C. That seemed to solve the thick string-thing, but I got problem with bed adhesion - as the print got loose after approximately 5-7 mm build height.

I then tried to revert to 255 / 70, but changed first layer height from 0,2 mm to 0,3 mm (my default is 0,2 mm both first layers and rest of layers).

To my big surprise - I just thought I could change the wall type from Arachne to Classic - and that resolved kind of everything - both the thick string at bottom layers, strings (thick, like filament-thick - like my last picture in my first post) fallen from the bridges inside and also the bed adhesion.

By the way, I wash my texture PEI plate with dish soap and water, and then use alcohol on it. Has worked perfectly with PLA.

I’m just confused. I know I have to use Arachne for small text of signs / business cards / coasters, but is Arachne worse than Classic now? In Bambu’s Wiki, I read that Bambu has changed from Classic to Arachne as default - but not in my (up to date) Bambu Studio - all the defaults from Bambu Lab in my slicer have Classic as default wall generator.

What would you recommend of wall types - do you have similar results?

[oddsandsods]

It looks like you are under extruding try increasing your flow ratio by 0.01 and see if it is and better, if it improves but still not there try a little more. Also if the stringing is coming from the overhangs or threads after adjusting the flow ratio try changing the wall print order to inner/outer this will give the outer wall something to stick to.

[Mici]

Whether you should use Classic or Arachne sometimes depends on the model. Both have their own advantages and disadvantages. I would recommend Arachne.
“detect thin walls” can also help sometimes.
https://wiki.bambulab.com/en/software/bambu-studio/wall-generator

I have an A1 mini too and have printed a lot of PETG. The prints are just gorgeous and I am still in love with this little quite speedy beauty.

Just a few thoughts (even though you’ve already figured some out):

• I have still many spools e.g. from Prusa, so I mainly use the Generic profiles and just sometimes change the temperatures.

• Nozzle temperature at max. filament temp. -10°C is a good point to start with

• Ensure to always raise the optimal bed temperature by ~5°C for the textured sheet. So if your have perfect adhesion with 70°C on the smooth sheet, you will need 75°C for the textured one.

• I don’t mess around with all the other settings, even though I mostly understand what the result could be. The automatic calibration is just magic and has done a better job than me so far. It also can help with slightly damp filament.

• The printed wall order can be very important. Just switch between “print inner/outer wall first” and have a look how the nozzle moves on the shifted layers in your slicer. The inner circle on the cube picture seems to me as it has to be printed with shifted layers, so this can be the cause. By printing the inner wall first, you’re almost air printing.

• Cleaning with soap and water is just perfect. Depending on the quality, IPA can even leave a very thin layer, which ends up with adhesionloss.

At least in my cases it was only the filament that was to blame, or myself.

Good luck.

[Gimbal]

What is the max flowrate you use for the PETG filament?

[ThomasB]

0.95 - and my K is 0.045.

[Gimbal]

My bad, I meant to ask for “max volumetric speed” set for the filament.

[ThomasB]

Hi,

Thank you all for your replies. It really means a lot to a Bambu-noob

@Gimbal, max volumetric speed is set to 8, as I have based my filament settings on the Generic PETG profile, and just adjusted a few details.

I just have to mention… My filament from Clas Ohlson (Swedish company with shops also in Norway, filament is produced by FlashForge, but it’s called Clas Ohlson PETG Universal) says 220-245 C on the box, but temp towers show me that 245 C and lower is no good. It’s matter in the finish, and artefacts in surfaces and bridges start to become visible on 245/250 C. That’s why I have stuck to 255 C. But shouldn’t this be wrong, when the vendor states 220-245 C? Just confusing, as you should think vendor knows best.

[ThomasB]

Thanks, @Mici,

I use almost only the textured PEI sheet, as my smooth plate was used when I got it, and it has some damages, so I avoided it after noticing the textured plate was way easier.

If you take a look at my temp towers, the temperature range from Clas Ohlson / FlashForge (filament produced by FlashForge for Clas Ohlson) 220-245 C is too cool - it shows artefacts and defects in bridges and surface. Well, they were before drying, after drying, I just printed 260-250 C. However, 255 C I have chosen based on that it looks better than 245 and 250, and also 260. I think… Am I wrong?

But it’s very strange to pick 255 C when vendor states 220-245 C on the filament box… Especially when you’re a noob to PETG (and Bambu).

I think PLA is very easy on the Bambu - it’s just PETG I find hard to print now. Even TPU (Add:North) is fine.

Inner/outer/inner has been chosen after watching a lot of YouTube videos and reading in forums that outer/inner (or especially inner/outer/inner) should give better surface finish. And my tests on PLA showed that, so that’s why I have stuck to it.

I have tried inner/outer, but I had to add Classic walls to the mix to get results for that bottom layer for the Bambu Cube V2 to get rid of that thick string. However, it was better on that print, but not on other prints. So I have switched back to Arachne, as that’s generally more recommended, it seems, and also Bambu’s WiKi states that they have changed to Arachne as default (although in my Bambu Studio slicer, I can’t find Arachne as default for any Bambu Lab presets, so I don’t get that they have changed it…).

But your way to get perfect PETG without stringing and any artefacts, is simply:

• Generic PETG profile, basically
• 10 degrees lower than max temp according to filament box recommendation
• You up the bed temp 5 degrees C for textured PEI plate
• inner/outer
• Classic walls, I guess, if you don’t change in Bambu Studio
• Cleaning with soap and water

That’s it?

[Gimbal]

I use Classes PETG as well, and also came to use 255 C at first, although lately I have dropped down to 250.
I have also changed max volumetric speed to 5, pressure advance set to 0.064 (using Orca slicer and standard 0,4 nozzle) and retraction override to 0,6mm. You should also mess with cooling settings.

As for Arachne I first thought it was great, one could print smaller details and sometimes it was also faster printing fewer lines. But I soon discovered that it also came with some quality problems so now my stand is, use classic whenever possible, and only try Arachne if classic doesn’t work.

[SupportAssistant]

It is not always a good idea to calibrate your filament settings based on the Temperature Tower test.

When printing other models, the printer will move faster and will probably extrude filament faster. Calibrating the temperature and settings for a model as small as this test can lead to incorrect settings that will not apply on larger models.

The default Generic PETG filament settings with 0.16mm layer height should work for most PETG filaments, if the filament has been dried well before printing.

A suggestion to further reduce stringing with PETG is to enable Avoid Crossing Walls feature which can be enabled under Quality → Advanced in Bambu Studio

Filament quality is important when it comes to print quality, and it can impact the results significantly.

[SiHCl3]

sometime u may turn off the slow down on overhangs to get a better quality of overhangs
just try……

[Mici]

@ThomasB

But your way to get perfect PETG without stringing and any artefacts, is simply:
This is not a cure-all, but just a few tips. As default I load PETG and press print. My A1 Mini does the rest

• Generic PETG profile, basically ← yes, if not from Bambu with RFID

• 10 degrees lower than max temp according to filament box recommendation ← As a start point for adjustments, if the generic profile does not work well for you

• You up the bed temp 5 degrees C for textured PEI plate ← BL studio does it for you when you switch from smooth to textured or back, but keep that in mind to fill in the right values

• inner/outer **<-there is no right or wrong, it depends to the model. Also very well explained in the wiki (see the link in my previous post)

• Classic walls, I guess, if you don’t change in Bambu Studio ← classic is default, right. But just read the BL wiki-

• Cleaning with soap and water ← Dish soap, best thing ever!

That’s how I do it and it was intended as a first approach, instead of changing all possible settings at the same time, as mentioned by SupportAssist too.

I can judge pretty well from the layers themselves whether the temperature is right. So it’s all a matter of experience.

• The faster you print, the less time your nozzle has to melt the filament. With such a high-speed printer, it can happen that the temperature has to be set even higher as recommended on the box to ensure the flow, so that would explain your results, at least in my opinion
• Check the setting mentioned in SupportAssistant’s post
• Use the automatic flow measurement until you entirely know your new printer. And than just use it still Believe me, it does a very good job.

To be honest, just use a new spool of PETG, use Generic profile and give it a try. I bet the most problems will be gone at once. You never get back the original quality once the filament became damp! At least not that way we all do. You just improve the print quality a bit, nothing more.

And if you point me to the model, I will print it and show you the result and which wall order I have used.

[ThomasB]

Thanks, @Mici,

The model of the Bambu Cube V2 is from the Bambu Studio:
Right click → Add primitive → Bambu Cube V2 from the menu

I think if that cube is perfect, it’s a good starting point, together with a 3D Benchy?

Temp towers I mostly run to check for the quality in bridges.

[Mici]

Thanks for pointing it to me, never realized that before. I am printing it now. Details follow…

[VictorLagina]

curious the difference between “detect thin walls” and “arachne walls” i always use the arachne and it in turn greys out the “detect thin walls” option…are they one in the same?

[ThomasB]

Wow - great. Very excited to see what you figure out.

[Mici]

OK, printed at 0.2mm with default settings (I only have changed the nozzle temperature a bit) and threw it to the printer.
The temperature is still a bit too low for this model, I see it because of the bridges and the layers, but I just can’t explain how I see it, like I can not explain how to breath, I just do

Even thought I would use supports for better looking bridges, I did not use any.

As a summary:

Are you new to 3D printing, or just new to PETG, or just new to BL printers?
In any case, I would still advice to read the BL wiki.

Is A1 Mini better or worse than P1S for printing PETG?
A1/A1 Mini is a great choice, no need to doubt about

All the settings you ask for to try to get rid of the stringing:
Speaking of the settings and differences about the wall generators, I would advice to read the BL wiki.
Damp filament ruins everything, stop the effort to find a workaround, just use a new spool and keep your filament dry next time.

Why does the model look better at higher temperature as advised by the manufacturer?
Because of the higher print speed your filament can´t reach that temperature in that short time. Its temperature is enough to flow through the nozzle somehow but is still way cooler then the nozzle itself when it gets out of it.
So a nozzle at >250°C may be able to ensure the filament is at least at 245°C during the print at high speed, which would be the temperature advised by manufacturer.
That is the idea behind the “high flow nozzles” and the “high speed filaments”.
Longer heating surface in the nozzle for more melting time and filaments that melt more quickly.

Best method to clean the PEI sheet?
Dish soap and water

I think if that cube is perfect, it’s a good starting point, together with a 3D Benchy?
For what start point? To check the bridging abilities, stringing, quality, temperature, tuning?
Unless you use high-quality and dry filament, you will always blame the printer or yourself and will never get a repeatable result to meaningfully evaluate your tuning results.

As you can see, my A1-Mini does not need any kind of tuning by default.

[ThomasB]

Thank you, @Mici,

I have read all the BL WiKis and I’m just new to the combo of A1 mini and PETG. I have 3D printed for years with PLA.

And I love my Bambu Lab A1 mini!

I have used completely new rolls with PETG from Clas Ohlson, and it should be fine. I’ve dried it anyways to be sure, and quality is much better after drying.