Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini  

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

I was monitoring the temperatures when I was investigating the PID settings and the temperatures were stable at the thermostat, so I suppose, there should be a varying temperature issue at the heatbreak above the hotend for sure. It can be a combination of thermal expansion/shrinkage on the heatbreak itself and thermal effects on the filament also... Maybe the diameter is not right, or the material behaves differently than expected, really don't know, but I'm sure that it is a bad design by default.

I noticed, that Trianglelab produces a similar heat-break, but from titanium, maybe it is worth a try.

https://www.aliexpress.com/item/1005001689822459.html

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

I'll order one tomorrow. Maybe it works. When it gets here. In a couple of weeks 🙂

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

What I found is that the problem is temporary fixed by filament change or cold pull. And it has a “memory”.

Here are the facts. I started with the brand new nozzle and Bondtech heatbreak. Printed in a raw two cubes 20x20x20mm in spiral vase mode – flowless! Then changed the filament and printed one more – again flawless!  Then decided that there is not problem with the replaced heatbreak. Later when the problem appeared again in my 3D prints I started using a bigger sized shape to check the issue – 40x40x30mm with at about 4 times larger area compared to the previous one in order to see the problem from the first 3D print. And what I found is that (facts):

1. If I do a filament change and immediately start 3D printing the shape the result is up to 50% OK. If I then immediately print another shape then the result is NOT OK.
2. If I do a filament change and immediately start 3D printing the shape the result is again up to 50% OK. If I then switch off the printer until it cools down (I waited a few hours to be sure that the time does not matter) and then 3D print the shape again then the problem starts appearing – NOT OK.
3. If I do a filament change and switch off the printer until it completely cools down and then start 3D printing the shape the result is again up to 50% OK.
4. If after the first print I do a filament purge and immediately after it start printing the shape the result is not OK. So purging do not fix the problem because the filament is not removed from the heat break.

Concerning these findings, I conclude that the problem has a “memory” and is connected with the amount of filament passed through the heatbreak at certain temperature. If it reaches certain amount/time the problem appears. And it is irrelevant if you stop the print and wait to cool down or not.

I also conclude that problem is not in the nozzle as the same nozzle prints flawlessly with another heatbreak. It is also not concerning the cooling as I am sure that the filament never reached the lower part of the PTFE tube. So it remains to be in the section between the nozzle and the PTFE tube. It is as if in this part the heatbreak starts retaining/accumulating filament until the clogging starts. Then after a while it partially releases filament and bulbs are formed. After this a new clogging is formed and so on.

Raising the temperature/changing the flow rate cleans the retained/accumulated filament and moves the process to another zone which will form the same problem after a while.

May be it’s connected with the filament heat creep that always forms.

The Prusa heatbreak moves this entire process into the PTFE tube zone. The problem is that during time the PTFE shrinks and a clogged is formed under it.    

Does all these thoughts make sense?

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

@prusatester2020

Have you tried with other types of filaments (PETG / ABS or ASA) ? This should help you in your investigation. I have a stock Mini but I only print with PETG and no issues so far. I had a clogged nozzle / heat creep after 2 days and it was right after I used the PLA sample...

Personally, I found PLA to be more sensitive to the environment and difficult to configure.

Also, is your Mini inside an enclosure ?

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Yes, it's inside an enclosure, but for some tests I used it inside a room w/o it, so the results are not connected to the enclosure. At present moment I have and print only PLA.

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Could it be the inside of the heat break is not smooth enough and accumulates micro amounts of material inside?

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Hey, just wanna follow this thread. Yesterday I recieved my Mini and I was also happy to get the + one.

While Assembling, I changed the Extruder for the Bondtech one, and tried out the stock heatbreak.

I got the same behavior like you did. First layers are perfect, nearly as perfect as my MK3S+ Bear. Printed some Cali Cubes, same behavior. Printed the pre-sliced benchy from the USB (0.15Layers) and problems started. First underextrusion and after a clog. Removed filament and it seems to be fine. -> Tested again - again a failure.

After that I changed to the Bondtech heatbreak - resliced - added PID to GCode - started in 0.15mm -> failure after 8-10mm.

Resliced in 0.2layers, set retraction from 3.2 to 3.0mm and added 8°C to the Nozzle -> failure after 22mm and totally failed with clicking and so on at 27mm.

Surface finish looks awesome, like I know it from my other Bondtech conversions.

There you can see the beginning of the weird extrusion and the complete failure. I Tested to pause the print and there came a big blob out at first, then it tries to continue until it finally stops.

So i took my thermal camera and found out there is something really confusing.

This is how my nozzle looks after heating to 210°C on my MK3S+ Bear and measuring 10 seconds after the temperature reached.

So I had a closer look to the Mini hotend and was a bit confused. 

Measured after heating to 220°C and let it stay for around 1 minute. Measured at the outer corner of the nozzle.

Measured after 2 minutes at the nozzle tip - 199°C?!

Measured the Cartridge directly - also a delta of 12°C (All measurements without the partcooling fan!)

So mini does his job, but there is something weird with temperature reading. Latest RC1 Firmware and nothing else done (tested also with the one supported at the USB - no changes). Full Temperature check done and no Problems. Could this also be a reason? So it's not really clogged because it's kinda cold extruding? The weird thing is, it's with bondtech and stock heatbreak :/ 

I'll contact the support later this day because there is something wrong. 

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Edit: Btw, measured also the Heatsink in the enclosure and outside of it, ranges after 1h printing are between 30-36°C so that shouldn't be a problem (at least for me and my testing with PLA first) 

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

I'm sorry but I do not have a thermal camera to compare the results. Your photos of the final print looks exactly as what I was receiving when using the Bondtech heatbreak. After I switched back to the original Prusa heatbreak the 3D results are excellent and there is no sign of under/over extrusion. Also the two other persons in the same thread share the same behavior.  

Would you please share a thermal photo of the thermistor cartridge - the place where the temperature should be measured. What is the temperature there!?! If it is not correct then the thermistor could be faulty. Also are you sure you use a brass/copper nozzle? Concerning the fact that the heater is next to the nozzle there is no excuse for the nozzle not to be properly heated EXCEPT if it's made from a strange alloy OR the filament manages to cool it down at a very fast rate. 

I will try to order a thermal camera (if it's not that expensive) to make same measurements.

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Thermal camera? Wow, didn't know one is required with 3D printer. 🙁 Expensive. Would usual temperature measurement suffice? I.e. one of those dual metal temperature sensor which can be fitted (and often comes with) a Multimeter? Naturally it is not as handy as a camera especially if the printer is moving.

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Have you checked Prusa mini thermistor values and compare them with the expected ones: https://help.prusa3d.com/en/article/multimeter-usage_2117

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Needed the thermal camera because there was something wrong on another circuit at home. Isn't mine, took it from work over the holidays. Wish I could achieve this thing, but as you said, it costs more than my mk3s and the mini together haha. 

I'll take some more pictures later. Also I'll "crosswire" the hotends (v6 to the mini and mini one to the mk3s) to have a look at thermal behavior (thermistor readings, heat behavior, and so on.) these are both the same 40w cartridges, so that should not be a problem. If the mk3 tells me the same wrong reading, I'll exchange the thermistor. This problem should indipendend from the heatbreak - maybe a bit lower heatblock temperature with stock heatbreak because the bondtech got a higher thermal resistance. Also I'll doublecheck the wiring and connection resistance.

Hope my thermal paste isn't a problem, used overkill Arctic silver. This will be my next thing to check. 

Glad it's holiday. Otherwise I would be a bit hard disappointed for waiting months for a mini and don't even finish a single (also presliced) print. My mini is Definetly not a beginner model. 

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

To the measurements, I'll check them before crosswiring. Problem would be, that it would not be possible to measure in "action" because of the thermal runaway protection. I could try to solder an adapter, but I don't know how good my dupont is prototyping cables are (need a really precise value, so bad connections would tell me nothing). 

As I'm an electrician, most of industrial equipment is either accessible because I bought it or at work.

Also bought one of these capricorn low friction heat resistant tubes as I wanted to have a look how these handle higher temperatures. 

Maybe I'll print a benchy with 235/60°C with different filament before I'll disassemble these 2.

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Posted by: @padigree

Hope my thermal paste isn't a problem, used overkill Arctic silver. This will be my next thing to check. 

Checking the Arctic Silver 5 product page it says:
Peak: –50°C to >180°C
Long-Term: –50°C to 130°C

So it doesn't really seem suitable for 3D printers, unless it's another Artic Silver product. 

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

According to this video:

it is possible to have difference between the resistance of the thermostat and the real temperature values and that could be fixed updating the temperature table in Marlin. Also at lower temperatures the readings could be OK but for higher ones there could be significant (10-15C) difference.  In case of Prusa Mini that should be fixed in the firmware. The reason for this difference could be that your thermostat is defective OR nobody checked the real measured values until now (WOW) OR this is done intentionally (conspiracy theory).

In all the cases this should be sent as information to PRUSA and what I think there is no way that they would say your thermal camera readings are inaccurate as you already compared them with another nozzle. I also think that there should be a separate thread in another section (may be in “Hardware, firmware and software help”) and as you now posses such an expensive equipment we will highly appreciate you to post as many readings in different scenarios as you can and keep us informed what PRUSA is going to state. As far as I can remember I have read posts complaining about Prusa Mini inaccurate temperature readings. I think that updating the temperature measurement table should solve the issue but if this is the case why Prusa haven’t done it yet?

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Thank you, already saw a kind of this video. I know there are (sometimes really hard) manufacturing differences. But I've never seen a problem that hard, not even with the cheapest China thermistors on my old anycubic printers. I've done my print with 230/60 and after 12mm increased to 240/60. Print finished - and is one of the most fascinating benchys I've ever printed (In the last 5 years). That mixture of perfection and absolute rubbish is truly some kind of art. And yes, I'm a bit disappointed, so I'll try to have a look on the positive side.

Funny thing - nozzle temperature varies like there is some kind of "broken" connection or lose thermistor. Really inconsistent temperature reading, so I adjusted temperature manually to get my 210-214°C on the nozzle. I'll upload some pictures of measurements and the print later before I disassemble the hotend again and start with my crosswiring.

Something I also thought of was a problem I've had earlier on an anycubic board (8bit). After changing the drivers to tmc2208, I noticed some lost steps while retracting - so if the filament gets pushed in again, you'll always have some steps more distance filament extruded than retracted. Nearly the same behavior. So I think the temperature problem is not the only issue I have. Next thing could be a test of motor current (hope that adjustment works on gcode?) or do some more retraction tests. 

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

May be this observation has something to do with our findings:

https://forum.prusa3d.com/forum/hardware-firmware-and-software-help/hotend-temperature-issues-clogging-temperature-seems-to-be-lower-than-read-assembly-instructions-for-hotend/#post-208664

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

I'm definetly done for today. I was sad when I noticed that the printer will not arrive before Christmas. Now I'm glad it didn't. Printed now over 300g of different filaments, with 2 little success. A Cali cat which lost her head while looking at her and a retract tower which seemed to solve all problems I had. Until the next half benchy. Measured, crosswired, replaced and so on. Disassembled the hotend 2 more times. I don't wanna even write the support, because I don't know how they could help me out. Rebuilt it complete stock, also problems. Tomorrow I'll replace the whole heater /thermistor combo out of my mk3 in hope it will work. Sadly i replaced my last spare thermistor 2 weeks ago, because the old one stucked to the original e3d block. So I replaced the whole block with new cartridge and thermistor. :/

Fun fact, most prints stopped after ~1h print time (2 times exactly 1:02h and one time 59min)

I absolutely don't understand this little thing. My hope was a little semi portable fun printer, now I have a bit bigger project. 

BTW, happy new year @all! 

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

Posted by: @padigree

I don't wanna even write the support, because I don't know how they could help me out. Rebuilt it complete stock, also problems  

Why not, at least point them to this thread to give some input, as you have issues with stock parts also. 
For me this is not really acceptable, as Prusa prides itself for quality (both products and support). 

RE: Strange extrusion problem using Bondtech extruder and heat break on Prusa Mini

i have just installed the bondtech heatbreak and seeing the same problems as you guys, i did the cube test after a filament unload then load. it was perfect (untill last few milimeters) then did another cube right after and there the problem got really clear. i have seen alot of people happy with the heatbreak upgrade, so is it just a bad batch or is there a fix they are not letting us know. dont see how some people are so happy with it