Nozzles becomes loose after 1 hr. print?
 
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1derman
(@1derman)
Active Member
Nozzles becomes loose after 1 hr. print?

Hello,

I am using a Prusa Mk3S and printing Nylon Pro from Matterhackers with a Nozzle X. My nozzle temp. is 260 and a bed temp is 70. I use Octoprint to run a bed leveling guide. I have modified my print bed using the nylon nut modification to make sure the print plate is as flat as possible.

I was wondering if anyone had some advice/suggestions as to what I should do if my nozzle keeps getting loose. You are probably wondering what I have tried to fix the issue. Well, I ordered a new E3d, 3rd party heat sink, heat break and heat block.  This issue started with the stock prusa heat block. I purchased a feeler gauge to make sure I have the correct 0.5mm gap between the nozzle and the heater block. I also purchased  a torque screwdriver that measures  0.8-5 Nm.

When I assembled the hot end with the new parts, I used a feeler gauge set at 4.8mm. I figured as long as it didn't exceed Prusa's recommended 5.0mm, it should be fine. Then I heated the nozzle to 285 for 1 and 1/2 minutes. Using the torque wrench, set at 2.2 Nm, I tighten the nozzle.  I reassembled the hot end and started the first print. Thinking the problem was solved, after printing for a couple of days, I noticed the first print was perfect, when the nozzle was at its tightest, then the rest of the prints, as the nozzle loosened, started to show issues that originally made me check the nozzle when the problem began. What did I do? I checked the nozzle, and indeed, the nozzle was loose again. By loose, I mean their was no resistance when I tried to unscrew it from the heat block. Is this normal, or do you agree the nozzle should have some resistance when I unscrew it? I did heat up the nozzle to 285 before retightening it.

After a second round and increasing the torque to 2.4 Nm, the problem continues. The only thing I can think of, is reducing the feeler gauge to 2.5-3.5 so the nozzle can be screwed in deeper into the heat block ;therefore, having more grip from the extra thread length ;in addition, I might increase the torque force to 2.5-3 Nm. If that makes any sense. What is the recommended torque force for tightening a nozzle on a Prusa anyway? I couldn't find a clear answer anywhere.

If any one can please help shed some light on the issue, I would be so grateful. I wonder if others have also experienced this problem, or are they printing along with a loose nozzle, thinking their nozzles are properly tightened. If my prints were not tolerance sensitive, meaning I need them to fit other parts, I would never have checked. I would never have thought their was a problem with the prints if I didn't need them to have the correct diameter clearance.

Much thanks if anyone stumbles across this topic.

Posted : 24/01/2022 8:51 am
Neophyl
(@neophyl)
Famed Member
RE: Nozzles becomes loose after 1 hr. print?

A correctly installed nozzle should not come loose.  At all.
Do you know why there is a recommended gap between the nozzle and heat block ?  Its allow leeway so that you can tell its fully screwed up against the heatbreak Inside the heat block.  The seal is between nozzle and heat break.  If its tight (to the recommended torque) then no plastic will leak out and the nozzle will not be able to move and unscrew.  You should not be able to screw the nozzle in any more as it physically butts up against the break.  The gap is so you can tell this.  The actual distance is immaterial.  Again - You are NOT tightening it against the Heat BLOCK but the HEAT BREAK.

Please have a read of this thread and look carefully at the image (which is from the Prusa knowledge base pages)

https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/what-happened-to-my-hotend/
The heat block is in effect just a large nut that allows the parts to be threaded together.  It also happens to physically hold the thermistor and heater cartridge but for the purposes of sealing its just a large nut.  

The prusa instructions are fine as far as they go but they don't really explain the reasoning behind it.  Probably because to some people its really obvious, unfortunately to others they just don't understand why immediately.

Posted : 24/01/2022 9:56 am
1derman
(@1derman)
Active Member
Topic starter answered:
RE:

Hi Neophyl,

Thanks for getting back to me with a potential solution. I followed this great little video in the prusa forums that I found under a thread by karl-herbert. I suggest anyone wanting to take apart their hot end and reassembling it take a look at this link: https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-hardware-firmware-and-software-help/loose-heater-block-after-changing-nozzles/

If you take a look, the tutorial explains why their should be a .5mm gap between the nozzle and the heat block. After following the tutorial as suggested, I am still encountering this issue. I am first screwing in the nozzle all the way, then backing it up using the feeler gauge to create the gap between the nozzle and the heat block, then I screw in the heat break into the heat block, tightening it with my hand, until it can not be tightened any further and is fully hitting up against the nozzle, inside the heat block. At this point, I heat up the nozzle to 285 and use the torque screw driver, set at 2.2 Nm, to tighten the nozzle, locking it up against the heat break inside the heat block ;therefore, ensuring their is no gap between the heat break and the nozzle inside the heat block. Am I doing something wrong?

The only thing I can think of, is reducing the feeler gauge to 2.5-3.5 so the nozzle can be screwed in deeper into the heat block ;therefore, having more grip from the extra thread length ;in addition, I might increase the torque force to 2.5-3 Nm. If that makes any sense. Do you think this might help? Do you know what is the recommended torque force for tightening the nozzle on a Prusa? I couldn't find a clear answer anywhere.

If you have other suggestions or advice as to what may be causing the problem, I would greatly appreciate your insight.

This post was modified 4 months ago 2 times by 1derman
Posted : 25/01/2022 1:50 am
BogdanH
(@bogdanh)
Honorable Member
RE: Nozzles becomes loose after 1 hr. print?

...or are they printing along with a loose nozzle, thinking their nozzles are properly tightened

-that's kinda impossible to be the case. The thing is, if nozzle becomes loose, then a gap between nozzle and heatbreak occurs, where filament runs out at the bottom and the top of the heater block -which is instantly visible.

There's no need to "measure" the gap between nozzle and heater block with a feeler gauge. The thing is, V6 nozzle has 1mm thread and so turning the nozzle by half rotation is exactly 0.5mm. And then, 0.5mm is only an arbitrary number (recommendation) and so 0,1mm more or less plays no role. Actually even 0.8mm gap would be ok. Important is, that there is a gap.. otherwise one can't tighten the nozzle against heatbreak.

About torque for nozzle.. Official E3D recommended value is 3.0Nm, Prusa recommends (for the same nozzle) 2.5Nm, and Bondtech recommends 1.5Nm. What does that tell us? It means it's not some exact science. We could also say "it must be tightened just enough (1.5Nm) and not too much (3.0Nm)".
I have tightened nozzles by feeling until I bough fixed 1.8Nm torque wrench and in both cases nozzle never became loose. However, it's important that we don't rotate heater block after tightening the nozzle!

[Mini+] [MK3S+BEAR]

Posted : 25/01/2022 8:43 am
AndersK
(@andersk)
Eminent Member
RE: Nozzles becomes loose after 1 hr. print?

I have not used the nozzle X but the special coating lowers friction. Great inside the nozzle but not wanted in threads really. This in combination with thermal cycling and different thermal expansion properties could cause it.

You could try to knurl the threads a bit on the nozzle to increase friction, old trick in many trades.

You can use a combination pliers but don't squeeze to hard.

Posted : 28/01/2022 10:24 am
Thejiral
(@thejiral)
Estimable Member
RE:

Forget the feeler gauge. Heat hot end to 285°C, screw in nozzle loosely, let it really reach the temperature of 285°C. Then screw it until there starts to be resistance and then just tighten it quickly with 1.5 to 3 NM, until it clicks at the given NM. When you are done. the Nozzle is installed. Only then check if you can see any sort of visible gap between Nozzle and hotend (0.1-0.5 mm, it's not rocket science, you don't need to measure it properly). If you don't see any gap whatsoever, something is wrong with your hotend and the nozzle is not properly pressed against the heat break but rather against the bottom of the hotend. If you see that gap, the nozzle shouldn't get loose, ever. 

PS: I have used Nozzle X once and had no problems with it staying where it should. 

This post was modified 4 months ago by Thejiral

Mk3s MMU2s, Voron 0.1

Posted : 28/01/2022 11:56 am
Neophyl
(@neophyl)
Famed Member
RE: Nozzles becomes loose after 1 hr. print?

Its not nozzle x related.  Thats whats been fitted to my printer for the last 3 years mostly.  Its my default nozzle, although I'd guess at this point its pretty much just a steel nozzle now as its seen some serious use.  Zero issues with it ever coming loose and I have done many swaps and refittings now.

Posted : 28/01/2022 12:33 pm
1derman
(@1derman)
Active Member
Topic starter answered:
RE:

Neophyle, I would agree with AndersK. Different metals react differently to the intensity of heat.  The harder the metal, the more intensity of heat is required. The  softer the metal, the less intensity of heat is required. Please correct me if I'm wrong.

This post was modified 3 months ago 2 times by 1derman
Posted : 01/03/2022 10:42 am
1derman
(@1derman)
Active Member
Topic starter answered:
RE: Nozzles becomes loose after 1 hr. print?

Neophyle, I would agree with AndersK. Different metals react differently to the intensity of heat. The harder the metal (nozzle), the more intensity of heat is required to manipulate the expansion.  The softer the metal (nozzle), the less intensity of heat is required to manipulate the expansion. Please correct me if I'm wrong. Check your nozzle after printing for at least 24 hours.  Copper is a softer metal. Hardened steal, hence, Nozzle X, is a hardened/harder metal; therefore, requiring higher temperatures.

Posted : 01/03/2022 11:21 am
1derman
(@1derman)
Active Member
Topic starter answered:
RE:

I forgot to mention, that different types of metals, require more or less torque strength. The harder the metal, the more torque. the softer the metal, the less torque. So copper nozzles or an Olson Ruby nozzle requires less torque than a Nozzle X. The 3DVerkstan torque wrench made for the Olson Ruby nozzle has a low torque strength. Using the 3DVerkstan for the Nozzle X is not a good idea.

This post was modified 3 months ago 3 times by 1derman
Posted : 01/03/2022 8:38 pm
David
(@david)
New Member
RE: Nozzles becomes loose after 1 hr. print?

Hi All,

I'm getting same issue of nozzle X getting loose and generating leaks (3rd time). This never happened before, I'm following prusa procedure and I understand how mounting should be made properly. I'm starting to have serious doubts with the nozzle X surface treatment. This time, I'll papersand the back side of the nozzle on my lathe.

Best regards

Posted : 04/04/2022 3:57 pm
Thejiral
(@thejiral)
Estimable Member
RE:

Nozzle X is not my standard nozzle but I have printed with it for some time, couldn't see any loosening issue on my Stock MK3s (E3d V6 hotend). I have it now on a dragon hotend as well and haven't had any issues there either. 

As described previously, I heat up the hotend, insert nozzle wait until everything has equilibrated at that max temperature and then screw it in to the final torque recommended. Done. Nothing moves. I personally don't care about the distance of the nozzle to the heatblock as long as it is visibly more than zero. 

If you papersand the backside of your nozzle you risk it becoming leaky as you reduce the overall length of the nozzle (even if you manage to papersand it 100% even on your lathe), with such a non-specification length the nozzle might be stopped by the heatblock bottoms instead inside of the hotend at the end of the nozzle thread. 

This post was modified 1 month ago by Thejiral

Mk3s MMU2s, Voron 0.1

Posted : 05/04/2022 1:42 pm
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