Changing the nozzle @ N2

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Tinkerer
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Joined: Mon Oct 09, 2017 8:30 pm

Changing the nozzle @ N2

Postby Tinkerer » Mon Oct 16, 2017 8:29 pm

Hi All,

did I get that right - one has to take out the hotend completely to change the nozzle?
No way of doing that with the hotend built in?
Kind a boring work, isn't it?

Jetguy
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Re: Changing the nozzle @ N2

Postby Jetguy » Mon Oct 16, 2017 10:48 pm

Well, the alternative is doing it wrong, putting torque on the thermal barrier tube, snapping it off mid process, not getting the nozzle tight and getting a leak.

So yeah, taking a couple of minutes to do it right, not damage an $80 hotend assembly, not cause a leak and make a massive mess.


Jetguy
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Re: Changing the nozzle @ N2

Postby Jetguy » Mon Oct 16, 2017 10:59 pm

It's not that you cannot do it in place, but it first requires understanding what you are doing, what you cannot do (put torque or bending force on the throat tube), what the critical design and assembly steps are.

For example, you could do it in place IF and only IF you have a way to hold the heater block while tightening the nozzle and ensure that no torque or force is on the throat tube. Due to the space around the heater block, this is largely impractical. The best way I know is with the heater rod removed insert a long hard round bar into the heater hole. Even then, the risk is still ever present of a twisting or bending force.
Only with the entire assembly removed can I feel the torque and tension as I tighten the nozzle and ensure that it properly seals to the thermal barrier to prevent leaks. This way, I don't strip anything out, bend it or snap it. Another example were stocking a spare hotend already assembled can pay off. You simply swap in a known good one, work on the bad one off printer, take the time and care to do it right, then keep it ready for the next time.

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Vicky@Raise3D
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Re: Changing the nozzle @ N2

Postby Vicky@Raise3D » Tue Oct 17, 2017 7:52 am

As Jetguy said above, taking the whole hotend off from the machine and holding the heating block to carry out the nozzle changing will be much more safe then directly doing it when it is fixed on machine. Or you may break the throat tube.
Here attached the instruction videos about disassembling hotend and assembling hotend:
https://www.youtube.com/watch?v=Q3EaDHNdlKU
https://www.youtube.com/watch?v=hobwePlokQc

Tinkerer
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Re: Changing the nozzle @ N2

Postby Tinkerer » Tue Oct 17, 2017 11:30 am

Last night I took a close look at the spare hotend I have here.
And understood why one has to take it out to change the nozzle - the throat tube is rather thin.

How much torque do you guys use to tighten the nozzle?
And is it necessary to retighten the nozzle after it has been heated up?

I watched the videos.
What I do not see is - why is it necessary to remove the heatsink as well?
I can unscrew the heating element without that step and then change the nozzle, right?

My intention is to install the V2H-nozzles these days - hope it's worth the efforts;-)

Jetguy
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Re: Changing the nozzle @ N2

Postby Jetguy » Tue Oct 17, 2017 12:57 pm

#1 Yes, highly recommend the V2H nozzle and that's the first thing done to my printers
#2 Why do you have to remove the heatsink? I was hoping you would catch this nugget of information in the threads I pointed you at.
The thermal barrier AKA throat tube screws in from the top, the nozzle screws into the heater block from the bottom. The "system" of the 4 basic parts of the hotend (throat tube, heatsink, heater block, and nozzle) Requires specific assembly steps and orientation. Again, if you read the links entirely, you would see that some users had leaks from improperly assembled hotends from the factory. Now in fairness, I think that was corrected however, you are putting a new nozzle in. The nozzle has a shoulder that must NOT bottom out against the face of the heater block without properly sealing to the thermal barrier inside the heater block and completely invisible. As such, the way you know it is sealed is that there is still potential for the nozzle to rotate and tighten towards the block but during the tightening sequence, you can feel the nozzle torque mate to the thermal barrier. Also realize the entire assembly has to be clocked AKA rotated to specific alignment. What I'm saying is, you may have to screw the thermal barrier AKA throat tube in 1/4 to 1/2 turn from factory assembly to make it further protrude into the heater block so that the new nozzle doesn't bottom out against the block before sealing properly to the throat tube inside. Failure to get this all right means the follow can happen
The assembly might be cocked such that the heater block and heatsink are not straight
The heatsink and heater block might be straight, but the nozzle bottomed out and did not seal
This is why you take it apart, use the jig as per the instructions and tutorial, that ensures alignment but the process and understanding the key assembly technical details you may take it apart and adjust it a few times until satisfied both that the nozzle has sealed and that the assembly is oriented correctly.

Last- at the same time, insulating the heater block while out is 10 times easier than trying to do it in the printer.

#3 how much torque. I don't have a numeric value but the idea is that you are holding the heater block and tighten the nozzle into it while with utmost care, ensuring the throat tube is aligned and does not rotate out of alignment compared to the heater block. But at the same time, you do not want strong force on the throat tube so primary holding is the heater block, with only light secondary force to prevent the throat from rotating. Obviously not so much torque to strip the threads and/or snap off the nozzle (and yes, have seen people snap off a nozzle before).

#4 Generally not needed to tighten after proper assembly. That said, a lot of that depends on proper assembly. If say you messed up before and got a leak, and the threads are contaminated or you failed to ensure the nozzle did not bottom out before tightening to the throat tube- it will leak and again and that plastic in the threads can prevent you from really understanding and feeling if it sealed to the thermal barrier. Just because the nozzle is tight to the heater block does not mean it was installed right. Especially true if the heater block can rotate around the thermal barrier- that's a telltale sign. Now what is bad is recent V 2 hotends have a 5th brass setscrew in the heater block that can tighten to the thermal barrier. This has the potential to mask this loose nozzle not sealed to thermal barrier condition during assembly.

What I do not see is - why is it necessary to remove the heatsink as well?
I can unscrew the heating element without that step and then change the nozzle, right?


No, for reasons I stated above, to be absolutely sure the new nozzle has sealed and not just bottomed out in the heater block without sealing- you SHOULD further inspect the assembly, understand the function of the 5th setscrew in the heater block, understand that the factory may have set the system with the factory nozzle such that a new nozzle may be very near to bottoming out against the heater block without sealing. So yes, you may have to undo the 5th screw, turn the heater block or throat another 1/4 to 1/2 turn, rotate the heatsink to match this new arrangement, tighten the nozzle with that 5th screw loose, then the last step is tighten that 5th setscrew Only after you 100% know the nozzle has sealed, the assembly is oriented properly for assembly into the printer.

Here is a quick edit of the stock picture for the V2 hotend.
V2 hotend 5th setscrew.jpg
Last edited by Jetguy on Tue Oct 17, 2017 1:38 pm, edited 2 times in total.

Jetguy
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Re: Changing the nozzle @ N2

Postby Jetguy » Tue Oct 17, 2017 1:02 pm

Before you ask why is the throat tube small and thin- this goes to basic extruder theory and why I call it and and am trying to help the terminology- the thermal barrier.

The throat tube screws into and mechanically connects the hot heater block and nozzle to the rest of the hotend and extruder assembly.
The thin cross section of metal and the specific metal used (I think it's titanium) has a relatively low rate of conduction. The 2 factors combine to limit the heat conducted upwards to an amount that the heatsink and fan can remove easily so that the rest of the filament path and the extruder does not overheat and soften low temp filament like PLA before it hits the melt zone of the extruder.

Basically, without a proper throat tube and heatsink fan combo- printing PLA and other low temp materials would jam near constantly.

Jetguy
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Re: Changing the nozzle @ N2

Postby Jetguy » Tue Oct 17, 2017 1:10 pm

Before you ask why sealant or an o-ring is not used to seal the nozzle:
Between the hydraulic pressure of several hundred pounds per square inch inside the melt zone and the high enough temps to melt plastic and TPU rubber- that's why you cannot use sealing compounds.

The seal must be metal on metal deformation. The throat tube tip presses against the inlet of the nozzle and even the V2H nozzle is still a brass nozzle under the coating and the brass deforms slightly at a microscopic level to form a tight metal on metal seal.

Why hundreds of PSI of pressure?
The filament is really small cross section area, not unlike a needle pressing into a surface. At only a few pounds of force pushing on the filament you reach several hundred PSI (Pounds per Square Inch) and because this is less than one square inch- that's why the number can be so high. And yes, this is valid and why the plastic will leak out of the tiniest of tiny gaps or holes in an imperfect seal.

EldRick
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Re: Changing the nozzle @ N2

Postby EldRick » Tue Oct 17, 2017 3:33 pm

I'd like to remove the hot-end, but the wires running to it are so short that I cannot drop the hot-end down at all.

How might I get another half-inch of heater and temp. sensor wires to allow me to remove the heater block?

Jetguy
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Re: Changing the nozzle @ N2

Postby Jetguy » Tue Oct 17, 2017 3:42 pm

You loosen the fan first. This gives you access to the set screws in the heater block locking in the cartridges. You loosen all 4 so that both the heater and thermocouple can slide out at the same time. You simply pull the block down enough that the mounting head on the throat tube is out of the central crossing block and then slide the heater block off of the thermocouple and heater cartridge while they stay still.

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walshlg
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Re: Changing the nozzle @ N2

Postby walshlg » Wed Oct 18, 2017 12:08 pm

One suggestion, look and see and make a note of where the fans connect to the breakout board and then UNPLUG them before working on the hotend. It is so very easy to slip and ruin a fan when removing those fan screws

EldRick
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Re: Changing the nozzle @ N2

Postby EldRick » Wed Oct 18, 2017 4:15 pm

My problem is that there is not enough slack in the wires running to the heater and thermocouple - I can't drop the assembly enough to remove it.

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Steven.W
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Re: Changing the nozzle @ N2

Postby Steven.W » Wed Oct 18, 2017 7:39 pm

EldRick!
Make sure to loosen each screw on the side hot end before trying to remove anything, and when you have all those guys loose they should be able to come out no problem. A bit of resistance is normal because, like you said, there isn't too much playroom when removing the heater rod and thermocoupler. Once those are out and you've removed the screw limiting the hot end's movement it should come down freely. If you have any issues getting it done still and have looked over all the advice here on the thread feel free to submit a ticket so we can better support you!
Steven Whalen
Raise3D

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walshlg
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Re: Changing the nozzle @ N2

Postby walshlg » Fri Oct 20, 2017 4:59 pm

EldRick wrote:My problem is that there is not enough slack in the wires running to the heater and thermocouple - I can't drop the assembly enough to remove it.


buy the newer thermocouples, they are much longer and better constructed


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