Hot End Filament Leak

Topics around mechanical design, controller and electronics. Mods & hacks welcome.
bfwalach
Posts: 12
Joined: Thu Aug 31, 2017 6:49 pm

Hot End Filament Leak

Postby bfwalach » Thu Feb 22, 2018 8:13 pm

Hi all,

Recently cleaned my hot end and swapped out the extruder head because of frequent jamming and filament leaking. I started another print and noticed it is leaking from the middle screw (left in pic) and also between the heat sink and heating element. Any ideas about what to do?

Brian

IMG_20180222_150734.jpg

User avatar
Vicky@Raise3D
Posts: 4138
Joined: Fri Mar 25, 2016 3:54 am

Re: Hot End Filament Leak

Postby Vicky@Raise3D » Fri Feb 23, 2018 4:58 am

Filament leakage is normally because the throat tube and nozzle are not well sealed with each other. A minor gap between will cause the melt filament leak out.
Have you checked our assembling instruction and followed step by step carefully during the reassembling?
Did you leave a minor gap between nozzle and heating block to make sure it has touched the throat tube already?

bfwalach
Posts: 12
Joined: Thu Aug 31, 2017 6:49 pm

Re: Hot End Filament Leak

Postby bfwalach » Fri Feb 23, 2018 7:52 pm

I followed the instructions in the video and disassembled the entire hot end, cleaned it and cleared out any stuck filament, and reassembled it. The video is inconsistent with the materials we received because, in the video, the extruder is not flush with the heating element. In both units we received, including one I am looking at now, the extruder is flush with the heating element.

In any event, the extruder is still leaking. I broke two of our four hot ends today trying to disassemble and re-assemble them because they were so stuck from filament leakage. I am putting some pics below.

Pics from the leaking extruder this morning:
IMG_20180222_151629 (1).jpg

IMG_20180222_150734.jpg


Stripped screw (3 of my four hot ends had stripped screws; they are tiny and strip easily)
IMG_20180223_080658.jpg


Reassembled hot end
IMG_20180223_082959.jpg


Leaking after two minutes:
IMG_20180223_144345.jpg


I am at a loss here.

zemlin
Posts: 353
Joined: Sat Oct 21, 2017 2:02 pm

Re: Hot End Filament Leak

Postby zemlin » Fri Feb 23, 2018 8:17 pm

- have your hot ends hot when you disassemble them.
- in the first photo it is apparent that the nozzle is shouldered on the body of the heater block. That is incorrect. You need to thread the throat tube further into the heater block until the nozzle seats against the end of the throat tube before it shoulders against the heater block.
- do the reassembly hot to ensure you don't have plastic preventing your parts from going together as required.
- I replaced the brass set screws in my hot ends with these:
https://www.mcmaster.com/#94085a091/=1bp5r55
The brass tip won't damage the threads. The steel body won't strip as easily as the brass screws. Don't use the ball-end of a wrench when torquing these little guys.

bfwalach
Posts: 12
Joined: Thu Aug 31, 2017 6:49 pm

Re: Hot End Filament Leak

Postby bfwalach » Mon Feb 26, 2018 12:44 pm

What's weird is the tool I used to line up the heating block suggested I should not go any tighter.

IMG_20180223_080236.jpg


However, when I tried to go tighter with another hot end, this happened:

IMG_20180222_143047.jpg

zemlin
Posts: 353
Joined: Sat Oct 21, 2017 2:02 pm

Re: Hot End Filament Leak

Postby zemlin » Mon Feb 26, 2018 1:28 pm

I watched those videos last night and was not impressed with their use of that fixture. The key is that torque needs to be isolated from the heat break in the throat tube, and that is not the case with their assembly fixture.

I swapped a nozzle yesterday. My method is to put an adjustable wrench on the heater block and torque the nozzle - not putting any torque on the throat tube. What I found was that when torquing the nozzle the throat tube would start to rotate in the heater block in spite of the brass-tipped set screw being tightened down as much as I dare.

Next time I swap a nozzle I'm going to remove the throat tubes and file flats on them where the set screw lands - the flats will need to line up with the flats on the upper end so the heater block orientation remains correct. With flats for the set screws it will prevent rotation of the throat tube in the heater block when torquing the nozzles.

bfwalach
Posts: 12
Joined: Thu Aug 31, 2017 6:49 pm

Re: Hot End Filament Leak

Postby bfwalach » Mon Feb 26, 2018 9:11 pm

Thanks for the input. I figured I would take everything apart again and try one more time. I found that the throat tube screwed an extra quarter turn past where it should finally line up with the heating block. This caused the extruder nozzle to sit up a bit more (as it should I guess), but it left the throat tube pretty loose. Threw it on anyway and while it's not leaking from the screw anymore, it is leaking up at the throat tube as expected. Pretty significantly. Do you (or anyone) know anything I can seal that off with?

At this point when the new hot end assemblies come in (we have two printers so I just ordered four more hot ends) I am going to try to start fresh and really not mess anything up. I think there is some user error here, but also I think the parts are very fragile.

zemlin
Posts: 353
Joined: Sat Oct 21, 2017 2:02 pm

Re: Hot End Filament Leak

Postby zemlin » Mon Feb 26, 2018 10:42 pm

bfwalach wrote: it is leaking up at the throat tube as expected. Pretty significantly. Do you (or anyone) know anything I can seal that off with?
The seal is the metal-to-metal contact between the nozzle and the end of the throat tube inside the block. You need to screw the throat tube into the block far enough that the nozzle cannot shoulder on the heater block.

bfwalach
Posts: 12
Joined: Thu Aug 31, 2017 6:49 pm

Re: Hot End Filament Leak

Postby bfwalach » Tue Feb 27, 2018 12:50 pm

zemlin wrote:
bfwalach wrote: it is leaking up at the throat tube as expected. Pretty significantly. Do you (or anyone) know anything I can seal that off with?
The seal is the metal-to-metal contact between the nozzle and the end of the throat tube inside the block. You need to screw the throat tube into the block far enough that the nozzle cannot shoulder on the heater block.


So I screwed it in as far as it would go and it was off by about 90 degrees so I went back a quarter turn and left it there. I assume that it originally stopped? Or maybe something came off of the piece? There's nothing stopping it at the exact point it should sit at.

zemlin
Posts: 353
Joined: Sat Oct 21, 2017 2:02 pm

Re: Hot End Filament Leak

Postby zemlin » Tue Feb 27, 2018 1:02 pm

bfwalach wrote:
zemlin wrote:
bfwalach wrote: it is leaking up at the throat tube as expected. Pretty significantly. Do you (or anyone) know anything I can seal that off with?
The seal is the metal-to-metal contact between the nozzle and the end of the throat tube inside the block. You need to screw the throat tube into the block far enough that the nozzle cannot shoulder on the heater block.


So I screwed it in as far as it would go and it was off by about 90 degrees so I went back a quarter turn and left it there. I assume that it originally stopped? Or maybe something came off of the piece? There's nothing stopping it at the exact point it should sit at.


Then you simply need to screw the throat tube deeper into the heater block by a half turn or more.

bfwalach
Posts: 12
Joined: Thu Aug 31, 2017 6:49 pm

Re: Hot End Filament Leak

Postby bfwalach » Tue Feb 27, 2018 6:18 pm

Well, the last time I did that, this happened:

IMG_20180222_143047.jpg

Jetguy
Posts: 2696
Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: Hot End Filament Leak

Postby Jetguy » Tue Feb 27, 2018 6:30 pm

Because you did it in the wrong order. You first unscrew the nozzle a 1/4 to 1/2 turn, then turn screw in the tube further that last bit so it lines up and is in further into the block and THEN tighten the nozzle while holding the block. You do not put stress or torque or try to turn the throat in against the nozzle as you will snap it.

Jetguy
Posts: 2696
Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: Hot End Filament Leak

Postby Jetguy » Tue Feb 27, 2018 6:36 pm

I screwed it in as far as it would go and it was off by about 90 degrees so I went back a quarter turn and left it there.

This is the exact moment you messed up and caused the leak. Instead of loosening the tube to line up, you loosen the nozzle first, tighten or turn in the throat tube so that it now lines up (it will not tighten, just turn in that direction to the next logical line up) and THEN tighten the nozzle back up inside. And while tightening the nozzle, you are holding the heater block and NOT torqueing against the throat tube or heatsink. It is only held lightly as the nozzle screws in and mates to it inside the heater block.

Jetguy
Posts: 2696
Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: Hot End Filament Leak

Postby Jetguy » Tue Feb 27, 2018 7:19 pm

Again, let's go over this decision point.
I screwed it in as far as it would go and it was off by about 90 degrees

So, at this point you cannot turn the throat tube to line up because it is mating to the nozzle too soon to rotate slightly more to line up as required.

If you choose to back off or unscrew to the next alignment= this causes a leak
If you choose to turn forward and attempt to screw in without first loosening the nozzle and screwing it out= you snap off the throat

So again, the correct answer is that you find when "screwed it in as far as it would go and it was off by about 90 degrees" is, stop trying to turn it in any direction (do not loosen or tighten it), loosen the nozzle, then turn in the throat freely because the nozzle is not blocking it until it lines up as required.

Now with both the throat screwed in far enough and aligned as required, then and ONLY then we hold the heater block firmly and tighten the nozzle. The nozzle should NOT screw 100% against the face of the heater block before it feels tight. That is how we know it sealed to the throat tube.

Again, key points here:
Never try to tighten or loosen the throat first. Always remove the nozzle and in doing so, never put stress, bending, or torque on the heatsink or throat tube. Always use the heater block as the main gripping point. I prefer to use a bar through the heater hole in the block VS using pliers or a vise to grip the outside of the block.
Always use a proper 6 point socket or tool on the nozzle, never pliers or a 12 point tool or socket. Also avoid an open end wrench (only 2 sides).
Never tighten the central setscrew until you are 100% sure the nozzle sealed to the throat tube. Having it tight during the sequence can make you think the nozzle is tight and in fact, it did not seal. In this case, if you loosen the central screw, the throat tube should not rotate or unscrew from the heater block.
Always inspect the nozzle to heater block from the side and the nozzle should not bottom out the hex shank against the face of the heater block. That pretty much guarantees a leak because you cannot sense if it just is able to no longer thread into the heater block or if it in fact sealed and stopped against the throat tube.

Forgot a big one: Never, ever use the ball end of the hex key on the setscrews in the heater block. ONLY use the square cut end (often, the short end of the "L", not the long end on the supplied hex keys). This is how you strip out the screw easily because the ball end has less contact.

bfwalach
Posts: 12
Joined: Thu Aug 31, 2017 6:49 pm

Re: Hot End Filament Leak

Postby bfwalach » Mon Mar 05, 2018 9:09 pm

Thanks for all the info. I think you're right and it's a bit of live and learn on my end. Ideally I wouldn't ever need to take the thing apart! I also wish I had purchased some thermal paste to use as that would have helped seal off the throat tube to the heater block. My new hot ends came in and they seem to be working well, so with all of the feedback you guys have given me, I should be able to take dare of it a bit better.

Jetguy
Posts: 2696
Joined: Tue Mar 22, 2016 1:40 am
Location: In a van, down by the river

Re: Hot End Filament Leak

Postby Jetguy » Mon Mar 05, 2018 9:51 pm

No, thermal paste will not seal anything. This is the first and biggest misunderstanding that even Raise 3D has done in the past. There are several hundred PSI of plastic pressure on the seal. This is why incorrect assembly will blow plastic right out of the threads. The only seal that is effective under this heat and pressure is metal metal deformation sealing. This is why assembly is so critical. What is actually happening is that when you tighten the nozzle into the heater block and it presses upwards against the throat tube also threaded in from the topside, the face of these 2 metal parts squishes and deforms making a seal. This is why once a nozzle is removed and inserted, the mating face of that nozzle may not perfectly seal again. It will have tiny scratches and deformation and if you do this multiple times, it may leak even when assembled correctly. Nozzles are consumable items and truth be told, the entire hotend has a limited number of cycles you can take it apart and install new nozzles before the threads fail.

I'm sure people doubt the PSI- but it's simple math. The filament cross section is only 1.75mm in diameter. It only takes barely 3 pounds of downward force to convert that to square inches and it's hundreds of PSI. The math works out that using 1.75mm filament, every 1 pound of force downward into the nozzle and hotend creates 267.7 PSI of pressure in the sealing area of the nozzle to throat tube.


Return to “Hardware”

Who is online

Users browsing this forum: No registered users and 4 guests