Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
Hello,
As already discussed ( https://forum.prusa3d.com/forum/prusaslicer/how-to-set-consistent-printed-layers ), I am experiencing a strange problem with under extrusion (extruding less filament causing drops/spills instead of a constant filament flow) immediately followed by over extrusion causing bulbs on the 3D printed model. This is clearly seen when printing in VASE mode at 215 ⁰C and lower using 0.4mm nozzle. I looked very closely the process and visually it looks like during a print the nozzle suddenly starts under extruding by spitting filament drop by drop and then over extrudes bulbs. This is clearly seen on a sunlight looking through the thin 3D printed model wall – first there is a thinner layer followed by a thicker ones:
The printed 3D models I used for testing are:
- https://www.udoma.org/tmp/PrusaMini/vase_cube_10mm.3mf
- https://www.udoma.org/tmp/PrusaMini/vase_cube_40x40x30mm.3mf
How to reproduce the problem:
- Use Original Prusa Mini and Bondtech heat break and Bondtech extruder. After a filament change start a 3D print of a 0.15mm 40x40x30 cube in vase mode (). The first layers are printed OK then bulbed layers started appearing more and more often. They are tiny and have to be checked using a magnifying glass. As you can see there always first a thinner layer followed by a bulbed one:
.
Here is what actions I have already tried and does not fix the issue:
- Changing the thermistor cartridge with a new one. I was suspecting the original thermistor was not showing the correct temperature.
- Changing the heater cartridge with a new one because the original heater was stuck and I had to change it together with the heater block.
- Changing the heater block with a brand new one because the thermistor and heater cartridges were completely stuck to the original heater block.
- Changing the tension on the Bondtech extruder using the thumb screw both up and down.
- Removing the filament sensor – I was expecting that it produces some additional tension that could cause the issue.
- Removing the filament spool and using a filament without any tension - I was expecting that the filament itself together with its spool could produce additional tension that could cause the issue.
- Replacing the heat break with a brand new one sent by Bondtech support team causes the same problem to appear. And yes, I put the heat break all the way up into the heatsink with the proper amount of thermal paste (the silver one that Prusa ships with the heater block). And yes, the PTFE tube is installed with the correct cone-shaped end facing down. And no, the PTFE tube is not flattened by the screw over it when tightened – on contrary I think there could be a small gap over it.
The main difference as far as I know between the Bondtech and Prusa heat breaks is that the Bondtech limits the heat spread only to the lower part of the heat break while the Prusa one lets the heat go upper reaching the lower part of the PTFE tube. Could this difference be the root of the issue? If this is the case why no one other complained about it?!?
- Replacing the nozzle with a new one. First time replaced by the original standard 4 mm brass nozzle and also with a brand new original E3D Platted copper nozzle.
- Setting the nozzle PID value based on the Bondtech recommended one. Also setting the PID value based on the autotune procedure.
- Setting the correct extruder E-Step motor setting using M92 E415 command. Also checked that this value produces the exact amount of filament as specified.
- Change the filament type/brand – tried with PLA Prusament Mystic Brown, PLA Prusament orange and also 1 additional type of PLA – same result every time.
- Manual extrusion of filament before 3D printing.
Here are my actions that fix the issue:
- Rising the temperature over 225 ⁰C fixes the issue most of the time.
- Filament change and then start a 3D printing process at 215 ⁰C. This action has a temporary effect for the first 10ths of layers then the problem starts appearing again. The strange thing is that if I do a filament change and start printing immediately OR after a few hours/day this fix always works.
- Changing the heat break with the original Prusa Mini heat break fixed the issue in the past. But after a long period of printing the original heat break starts causing clogs and I would like to start using the Bondtech heat break.
- Contacting Bondtech support – they have no idea what could cause the issue and replaced the heat break. I already sent them the old one for investigation.
Photos:
- A small cube (20x20x20mm) 3D printed in vase mode at 215 ⁰C – you see the bulbs:
- Same small cube 3D printed in vase mode at 215 ⁰C after a filament change – excellent print:
- Same small cube(s) 3D printed in vase mode at 215 ⁰C after a filament change in sequence from left to right – you see the problem appearance progress:
- A big cube (40x40x30mm) cube 3D printed in vase mode at 225 ⁰C – no problem at all:
- Same big cube (40x40x30mm) 3D printed in vase mode at 215 ⁰C after a filament change – you see how the problem started appearing from the middle of the 3D print:
- Same big cube (40x40x30mm) 3D printed in vase mode at 215 ⁰C – a closer view. Asyoucan see there is first a thinner part followed by a thicker bump:
- Filament end view after unloaded from the heat break at 215 ⁰C -is it ok?:
- Purged filament from the Nozzle by using Prusa Mini purge function from the menu – I think the inconsistencies are caused by the gear wheels of the extruder:
If I did not find the solution the next steps I consider are (are they correct?!?):
- Change the extruder motor with a new one to eliminate the motor from the equation.
- Change the Bondtech heat break with the original Prusa Mini heat break.
- Change the Bondtech extruder with the original Prusa Mini extruder.
Finally, I have the following questions:
- Did any of you ever experienced something similar?
- Any idea what is the exact cause of the problem?
- How to fix this issue and continue using the Bondtech heat break at 215 ⁰C and lower?
Thank you in advance 🙂
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
Hi, just to assure you, I’m having the same issues as you with the bondtech upgrades. I suppose it’s related more to the heatbrake AND retraction settings, as my standard thicker prints are fine, but the thin walled ones including more retractions are failung like yours. Did not figure out what causing this though, but after a cold pull, everything is fine for the first print, after it fails. I had my thoughts shared in the bondtech upgrade topic a few days ago.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
Oh, the topics:
https://forum.prusa3d.com/forum/hardware-firmware-and-software-help/inconsistent-extrusion-4/
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
Additional info:
- Replaced the PTFE tubes: the one between the extruder and the heat break and the one inside the heat break with a brand new ones – did not fix the issue.
I tried playing with different Flow Control settings at 215C. As soon as I raise the flow percentage (for ex. from 95=> 100=> 105 .. 120) the 3D print continues OK until is spoiled again after a few minutes. The latest I tried was set the Flow control to 120 on Prusa Mini. Everything started OK with a thick wall until suddenly again started under extrusion and splitting filament like marching ants (Mystic Brown looks purple then printed as a thin layer otherwise it looks brown):
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
Yes, it is quite exactly the same for me also. When I clean the hotend, doing a cold-pull, things will be normal, but by the time things deteriorate like on your pictures. It got to a point that the extruder started clicking also, so I started to investigate from an under-extrusion side... The thicker parts are blobs formed by the retarded extrusion... A partial clog holds back the extrusion, therefore it under extrudes, but after a while, because of the back-pressure it "cleans up" in form of a blob.
First I thought that it should be the extruder itself and it works inconsistently, but I really don't see this behavior when printing bigger, more simpler parts without too much retraction, but I instantly face it when doing thin wall or retraction-heavy prints. Somehow I think that the heat-break itself cools the filament down during retraction, somehow slowing down the flow rate, causing intermittent under extrusion.
You did mention that reverting back to the original prusa heat-break solved this issue for you, isn't it? (of course generating other, heat-creep related ones)
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
Yes and I ordered a new Prusa Mini heat break to check it again, bacause the original one had an incident ...
In Spiral vase mode there should be NO retraction - just test it 🙂
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
@prusatester2020 while this thread is a problem solver, its a really good example of how to troubleshoot and present the problem, even though I don’t have anything major to add, its been really good seeing your process and testing.
you mention putting it to 225 is a fix most of the time, is there an issue you find just setting pla to that temp by default in a filament profile?
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
I just tried reinstalling the stock heatbreak. It blocked and started clicking at the second layer of the test cube print.
I then shortened the PTFE tube in the heatbreak, and then I couldn't even complete the first layer calibration before the extruder started clicking.
I'm installing the bondtech heatbreak again now.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
I've done three consecutive prints in vase mode (simple 2cm cube, 215C at the nozzle, 60C bed, 0.15mm layer height, 0% infill, with five bottom layers, 0 top layers, vase mode). From cold start, the first print went quite well, the second and third both have some issues... It's a quick 8 minute print, from here:
https://www.prusaprinters.org/prints/41442-guide-flow-e-step-calibration-cube/files
It tells me, that it's not directly related to retractions, as it in vase mode, it doesen't do that, so it's still a mistery... I'm doing a different print now, but later, I will exchange the heatbreak for the original prusa one and run the test cubes again.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
@prusatester2020 while this thread is a problem solver, its a really good example of how to troubleshoot and present the problem, even though I don’t have anything major to add, its been really good seeing your process and testing.
you mention putting it to 225 is a fix most of the time, is there an issue you find just setting pla to that temp by default in a filament profile?
If I set PLA to 215C and then start printing using Bondtech heat break and if it is not after a filament change, the result is not OK. Rising the temp a little to 225 solves the issue for some time. Otherwise I usually print at 215C.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
I just tried reinstalling the stock heatbreak. It blocked and started clicking at the second layer of the test cube print.
I then shortened the PTFE tube in the heatbreak, and then I couldn't even complete the first layer calibration before the extruder started clicking.
I'm installing the bondtech heatbreak again now.
Are you sure you removed the "M92 E415" line when you returned the original one? If not then this explains your results.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
I've done three consecutive prints in vase mode (simple 2cm cube, 215C at the nozzle, 60C bed, 0.15mm layer height, 0% infill, with five bottom layers, 0 top layers, vase mode). From cold start, the first print went quite well, the second and third both have some issues... It's a quick 8 minute print, from here:
https://www.prusaprinters.org/prints/41442-guide-flow-e-step-calibration-cube/files
It tells me, that it's not directly related to retractions, as it in vase mode, it doesen't do that, so it's still a mistery... I'm doing a different print now, but later, I will exchange the heatbreak for the original prusa one and run the test cubes again.
Now you see the problem? Tried printing it at 0.10mm heigth? Tried printing for 30 minutes and see what's we are talking about?
And please don't forget to remove the "M92 E415" setting/line when using the original heat break!
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
Thanks for the reminder, though the E415 is the esteps value for the extruder, the heat-break related setting is the PID value setup: "M301 P13.54 I0.98 D46.58", which should be removed.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
@prusatester2020
M92 E415 is for the extruder, which is still the Bondtech.
I did do a PID autotune and was using the new values for the stock heatbreak.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
how do you do an autotune on the mini? via octoprint? as far as I know, the mini does not have an in-built option for that
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
@peter-susan
Yes. Octoprint.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
I'll do an autotune then, will see three cubes with the new values, then exchange the heat-break for the original one without any PID setup, then with autotune. Great post-christmas exercise 🙂
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
@peter-susan
I did the auto tune when I first installed the heatbreak and extruder. I still had the problem.
Octoprint is nice though. So the time to set that up is not completely wasted 🙂
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
I just tried reinstalling the stock heatbreak. It blocked and started clicking at the second layer of the test cube print.
I then shortened the PTFE tube in the heatbreak, and then I couldn't even complete the first layer calibration before the extruder started clicking.
I'm installing the bondtech heatbreak again now.
If the stock heat break blocks on the second layer that means in most of the cases that the PTFE tube is not properly installed and the heat break PTFE tube bottom is not clean. All these will let the filament clog very fast.
RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini
@prusatester2020
I know. That's why I took the PTFE tube out and shortened it. It was also correctly tensioned between the heatbreak and the screw for the bowden tube.
There was also no filament leaking anywhere.