How to clean a hotend stuck with TPU ?

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How to clean a hotend stuck with TPU ?

Postby davidbha » Sat Apr 25, 2020 11:36 pm

I have printed for the first time on my Pro2Plus with eSUN eTPU-95A transparent filament, and even succeeded to find such settings that enabled me to print the first 9 layers without any problem, when I suddenly observed that from layers 10-12 the printer actually printed in air, without any filament extruding from the hotend. The hotend moved as if it was printing as usual, but nothing came out of it.

It seems that if I wouldn't stop it, it could continue printing for hours in this virtual mode (with clogged hotend) till the end.
I intended to let the printer work all through night, and if I hadn't accidentally discovered this malfunction, the virtual print would have continued that way till the morning.

1) How can I clean the clogged extruder/hotend ? Is there any tutorial that explains how to do it ?

2) How such a malfunction (in which the printer didn't feel that the filament is not advancing for a very long time) can happen without any warning ?
3) Why the first 9 layers made good progress and only after a long time (about almost 3 hours) the problem began ?

Thank you.

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Re: How to clean a hotend stuck with TPU ?

Postby Markus64 » Sun Apr 26, 2020 7:54 am

That seems familiar to me! The same thing happened to me two weeks ago. I unscrewed the hotend and noticed that both the nozzle and the throat tube burned into the aluminum so that a normal unscrewing was not possible. In my case, the blockage was above the heat sink and relatively easy to remove. That is exactly why I am now converting my Pro2 to liquid cooling.

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Re: How to clean a hotend stuck with TPU ?

Postby Daws » Mon May 18, 2020 7:26 am

I had the same issue recently, I've never printed with TPU before and used the Ideamaker profile to run a test print, mine jammed after the first layer.

The real problem was when I came to clean the hot-end. I have watched the Raise3D you-tube tutorials and have good mechanical sensibilities. After removing the throat tube securing grub screw, I found that the tube was effectively seized in place and would only turn with a lot of effort (I heated it up as per the instructions using the printer heating element, this did not help. I removed the whole hot-end assembly and gently heated it with a small butane pencil torch and also used some freeze penetrating spray, neither of these approaches worked. I decided to persist with removing as I had ordered a spare throat tube and as expected, the throat tube snapped at the undercut section. I removed the broken part by drilling and retapping as the thread had become damaged by unscrewing the throat -tube.

I had ordered a new V2 hot-end complete from my local dealer and when it arrived I decided to strip it down and add some copper anti-sieze past on the grub screws and threat tube threads. Trying to remove the throat tube on this brand new un-used exruder was quite difficult and when it was removed, I could see evidence of aluminium galling on the steel threads. It has not been cross threaded but it does not spin on like it should do as shown in the assembly video.

Assuming the thread is cut correctly on the throat tube (assume this is CNC turned with a single point threading tool) my only explanation is that the cross drilling with the locking screw has not been adequately de-burred and this has caused the throat tube to pick-up material and damage the thread, this would be very obvious when it is assembled in the factory.

Long story short, has anyone else noticed that it is difficult to remove the throat tube?
CAD-NX Printer-Raise3D N2

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Re: How to clean a hotend stuck with TPU ?

Postby Jetguy » Mon May 18, 2020 11:53 am

Sorry, just saw this was a pro2, however there were signatures showing N2 so I was a little confused.

Yes, the Pro2 hotend OEM V2 or whatever you want t call it is a piece of junk IMO.
For all the reasons said in this topic carried over from the N series V2 hotend, but then, Pro2 also has LESS heatsink and poorer airflow!!!
That and the moving nozzle mechanism that leaves mechanical gaps in the guiding of filament like flexible allows the filament to buckle and jam from being pushed down by the feeder.

So yes, there are ALSO discussions on modified hotends for Pro2, either E3D based adapters like was made for the N series, or water cooling mods. To date though, very little discussion on the path between the feeder at the top and through the nozzle moving system and the problems there inherent to the moving nozzle design.

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Re: How to clean a hotend stuck with TPU ?

Postby Jetguy » Mon May 18, 2020 12:14 pm

Topics lik ... ins#p50642 ... ins#p46152

N series topic, but shows the N series E3d hotend system and other details discussion TPU on that printer. ... ods#p35054

The gap and where flexible filament can buckle on the N series, but ALSO likely similar gaps in the Pro2 moving mechanism also causing TPU to buckle. ... 580#p28580

I was able to radically improve the performance of the N series with TPU, however Pro2 presents far more of a challenge.
Different hotend mounting- a clamp system already not great with very limited contact and mounting pressure compared to the system of N2 hotend mounting.
Shorter Pro2 hotend design to compensate for the additional height of the moving mechanism. Hence why less fins, different mounting and so forth of the hotend compared to an N series.

So many reasons why I feel Pro2 was not necessarily an leapfrog improvement claimed over N series.
Just the fact was- about 2X more expensive.

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