Max volumetric speed with 0.2 nozzle

Bambu Lab X1 Series
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I always wondered why the 0.2 nozzle profiles have the max. volumetric speed so very low (2 mm³/s for PLA, while the other nozzle sizes has it as 21 mm³/s). Bambu’s explanation is to mitigate risk of clogging. I can see that a 0.2 nozzle is easily clogged by particles but why would a higher speed increase the risk? If anything, you’d think that a lower speed could increase the risk of overtaxing the heatbreak and cooler fan. Anyway until now I just half heartedly accepted it, sometimes using Ludicrous mode (which I never use for anything else) and sometimes just bumping it to 5 or 10 mm³/s. I’ve never had a clog ever - not with any nozzle size for that matter.

Today while I was playing with speed/flow towers I put the 0.2 nozzle to the test before calling it a day. No dual heater on this one, I reckon that would be completely redundant. Just a stock 0.2 hotend. But I made the speed tower all the way to printer’s max speed and then some.

It printed just fine without any strength issues, up to just under 25 mm³/s where the 500 mm/s limit kicked in. In my quest for the mythical clogging I let it continue and it completed the rest of the tower pegged to max. speed. No clog, no strucural artifacts. Admittedly there were cosmetical surface issues past 200 mm/s and 9.5 mm³/s or so, but no issues with strength or layer adhesion. And no clogging.

So I still don’t get it. Why would there be even a theoretically increased risk of clogging, so severe that they limited the VFR to 2 mm³/s when it can do 25 mm³/s? Have I just been very lucky? I think I will set my 0.2 profiles to 25 mm³/s and use that until I see a problem. I can keep outer wall speeds below 200 mm/s for looks.

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I haven’t tried the 0.2 nozzle yet myself, but I fully agree with you. I don’t see at all, how a high throughput should increase the risk of clogging.
The only risk I see is either with filaments that contain particles like many of those effect PLAs and filament that tends to carbonize if it stays heated for too long, which should be less of a problem the faster you print.

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I haven’t played much with max volumetric speed settings at all. I’m more about quality over speed, especially with small sized functional prints.

Question: Does changing the max volumetric speed affect the filament change process?

As I said in Reasons to use cool plate or engineering plate? I get clogged 0.2 nozzles mainly when changing filament types.

The worst is going from PLA to ASA. The temperature the firmware uses when loading ASA is high enough to semi-crystalize PLA and cause the nozzle to clog.

I have one 0.2 nozzle sitting around that is permanently clogged from going from PLA to ASA. I try unclogging it with various methods every-now-and-then, but I think it’s it lost cause.

I now have a habit of sitting in front of the printer when changing to ASA (I use this a lot) and listening for “clicks” of the extruder teeth skipping on the filament. As soon as I hear that I stop the print and start a series of “cold pulls” to clean out the nozzle.

Sometimes I get forgetful and just let it print and the filament starts to get stripped, and I pay the price. Prints fail, ASA gets stripped off and stuck in the filament sensor and the teeth in the extruder just clogged with ASA (they look almost smooth). So, I end up pulling everything apart and cleaning things out (I’ve gotten really good at that too).

But sometimes the filament changeover is fine. Go figure. Another thing I’ve noticed that all is well, when the printer is purging the ASA over the waste shoot the filament streams straight down. If it starts curling in circles either up/down or round and round it’s time to clean out the nozzle.

I use Bambu filament on all my prints (love the refillable spools, just wished they offered it on ALL their types of filaments in the USA). I also wish that there was a way to manufacture CF infused filament that is compatible with a 0.2 nozzle.

But I have to admit, this printer does AMAZING small prints with the 0.2 nozzle. I came from an Ender 3 S1 Pro and the difference is night and day for quality and ease of use (minus what I said above).

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Cleaning filament might help when switching between ASA and PLA.

Otherwise you could have different nozzles for PLA and ASA, but that might get annoying if you have to switch them too often.

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CF-infused filament is basically putting chopped-up (more like finely ground) fiber strands into plastic, so even if you manage to get fine enough fiber particles in there to not clog 0.2 nozzles, the additional strength gain, which wasn’t marginal to begin with, will be minuscule. So unless you like the texture/feel of cf infused plastics, there is no gain

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Ive been struggling with high temp materials with 0.2mm nozzle, mainly ASA. It gets clogs not in the nozzle but the throat. I guess because it sits there for a long time the filament gets tempered/annealed and turns into rock! Almost impossible to clear. I have my flow at 6mm³/s. I tried playing with temperatures but not luck. I need to do some white text on a black box and it looks horrible with a 0.4mm nozzle, even with arachne and some other settings to optimize for text. I have some 0.3mm nozzles on the way as a compromise. The only high temp filament i found that flows well from the 0.2mm is PC as its hard enough not to soften due to heat creep.

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@Warmup : Yeah… I know. It’s just a pipe dream that we can get some CF strength while using a 0.2 nozzle.

@maximit : Yep. ASA has been the worst for me too. But one thing I have found that help GREATLY is to dry the living life out of the spool of ASA. I bought the newest SUNLU filament dryer (they put in a fan and vent/filament holes in the cover) and it really has made a difference. It won’t do what Bambu recommends for temp and time, but I found running 2 cycles in the filament dryer works.

Side note: I FINALLY got the clogged 0.2 nozzle cleaned out. I disassembled it, used a propane torch and a hex key to get the majority of the filament out. Then I put acetone in throat of the nozzle and let it sit and used a pipe cleaner to start wiping it out. More heat, more acetone, rinse and repeat several times (always making sure the acetone was proper evaporated and blown out with compressed air). I wish I had a way to look down the throat of the nozzle to verify. But seeing clean pipe cleaners was the only thing I could use to judge.

P.S.
@the_Raz sorry for sidejacking your thread about the Max Volumentric speed. I will try to experiment myself to see if uping the volume has any affect.

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@the_Raz I finally got caught up on all my 0.2 nozzle prints and I found I had time to experiment with Max Volumetric Speed settings.

I used Orca Slicer and use its calibration tool of Max Flowrate. I used the following settings:
Start Volumetric speed: 1 mm³/s
End Volumetric speed: 6 mm³/s
Step: 0.5 mm³/s

After printing, measuring and doing the math, the highest MVS I could achieve with any filament was 5.25 mm³/s with a 0.2mm nozzle before the print failed.

So, I am really curious on how you were able to obtain such high volumetric speed?

1 Like
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IMG_6576
IMG_65763082×1363 994 KB

It was 100% stock hardware and Bambu PLA Basic. I set it from 1 to 72 mm³/s in steps of 1 IIRC, although it would actually top out at 24.76 mm³/s because that is 500 mm/s which is a hardware limit.

Edit: It was more likely 1 to 36 mm³/s in steps of 0.5

Edit2: I may have used something like this to increase the temperature with speed. Can’t remember.

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I just started using a .2mm brass nozzle (M6 .2mm w/ Aftermarket TZ2 hotend).

When printing ESun PLA+ and using a .4mm CHT nozzle (my typical use), I get about 29mm^3/sec.

But when I swapped the nozzle, today, and tried to do the ‘Load’-Filament, It wouldn’t work because the gears would push too hard and the back-pressure led to the extruder stripping on the filament. [Same 220 temps as with .4mm Nozzle]

This may be a result of not having changed the nozzle from .4 to .2 on the printer’s setting itself. Thus, the P1S may use a general extrusion rate for different nozzles: when purging and loading filament.

This would be my expectation for why the flow rate on a .2 preset is so incredibly low (~2mm^3/sec).

I just started working on PA calibration, etc. But I would expect that the race-track flow-rate calibration method, for flow-rate, might be a necessity: when using such a small nozzle.

The clogging risk that Bambu might be concerned with may result from PLA Heat-creep and excess back-pressure. Although, that wouldn’t necessarily seem all too sensible: as pushing more plastic (at an increased flow-rate) would help cool the nozzle, hotend, and most importantly the cold-end.

So it may also be an expectation that clogs may occur when trying to print faster w/ materials that have non-homogeneous filaments (wood-filled, Carbon fiber, etc… which they don’t recommend using in the first place.)

I’ll have to try a flow-rate test and watch for extruder stripping, as it was clearly the cause of my initial troubles.

You’d expect that a .2mm nozzle may require something like 1/4 of the flow-rate that a .4mm nozzle would use: given, [ pi * (.1 ^ 2) ] / [ pi * (.2 ^ 2) ] => 1/4th. Thus a typical 16mm^3/sec flow-rate would seemingly be reduced to 4mm^3/sec: assuming the pressure against the extruder is ~proportional… But I suspect that the back-pressure may not be linear.

It’s probably just best to run a calibration and see when the print shows artifacts or the extruder skips.

2 Likes
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Imagine a bottle . If you put too much water into it at a time, it fills up the chamber fast, the hottest filament will pass through the middle, while the coolest filament will always be on the edge of the bend of the nozzle opening and the angle there makes it flow slower than the rest in the middle. If you use more volumetric flow, into the chamber than can exit, the hottest filament will always come out in the middle, and the ones on the side will cool down a bit little by little, and in the end there is almost no room in the middle for even hot filament to pass through, and you have a clog.

If the volumetric flow is just right, it is almost like when you have your sink full of water, and you swirl the water to create an air-opening in the middle, the filament will drain faster, even from the sides, because there is not so much pressure on the sides, and the risk of clogging is less.

I believe the prinsiple behind Bambu’s reasoning for a low flow on 0.2 is something similar, although maybe not exact.

Toffypops

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I don’t think this is true. In my opinion, the filament on the walls is the hottest because the nozzle is heated from the outside. Typically, the filament in the middle is the coolest, because it only gets heated indirectly by the filament on the outside. That is why CHT nozzle are so effective: The filament is also heated from the inside, so the temperature is much more uniform and you achieve much higher flow before unmelted plastic reaches the nozzle.

Apparently, much higher flow rates are possible reliably than the values in the BambuLab profiles.

I have the feeling, that BambuLab didn’t invest the time to create good profiles for the other nozzles and just entered a very conservative value to be on the safe side.

1 Like
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if that is true, then getting a clog is more likely with a smaller nozzle like 0.2 since any filament can be like a plug coming down the middle. Nomatter how it is seen, higher flow on a small nozzle would risk clog. :smiley:

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Smaller nozzles definitely are more at risk of clogging. That is mainly because even small particles can get stuck in the orifice, that would just go through a bigger nozzle.

If flow rate is too high, then the force needed to push the molten filament through the nozzle can rise so high that the extruder will strip the filament and then nothing is extruded at all anymore. I wouldn’t call that a nozzle clog but rather a clog in the extruder, because the nozzle doesn’t block the extrusion.

What @the_Raz was complaining about is, that the max flow in the Bambu presets for the 0,2mm nozzle are far from what the printer can do.

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To lower the flushing temp of ASA you can add this snippet to your change filament gcode in the printersettings

{elsif filament_type[next_extruder] == “ASA”}
M109 S245

For some reason pasting gcode here borks the code… so just manually type the above snippet into the gcode so it looks like the one below :slight_smile:

DO NOT COPY PASTE THE FOLLOWING. IT WILL THROW AN ERROR.

; FLUSH_START
; always use highest temperature to flush
M400
{if filament_type[next_extruder] == “PETG”}
M109 S260
{elsif filament_type[next_extruder] == “PVA”}
M109 S210
{elsif filament_type[next_extruder] == “ASA”}
M109 S245
{else}
M109 S[nozzle_temperature_range_high]
{endif}

I set the temp to 245 for you as that should be juuust enough to soften the asa and not cook the pla.

Hope you like it as much as i did.