Hot End and Extruder Building Questions

Hi,

I'm quite new at this 3D printers world but I'm starting a project where I'll try to develop my won 3D printer arduino based.

I've been doing lots of research, reading articles and watching lots of videos, but most of the information refers to already-built printers, kits or upgrades for commercial printers so I actually miss some details abot how it works. Anyway I'm now specially centered on hot ends and extrusion and there are some base questions to which I can't find an answer, let's see:

As far as I know a hot end is the device that heats the filament until it's melted. So, the filament is pushed by a stepper motor, it melts down in the hot end and it goes out through a nozzle. My questions are:

- I can see everywhere "hot end temperatures" (like 240 C for ABS), can I assume that is the temperature on the inside surface of the hot end? or even further, if I were using nichrome wire around a barrel, could I assume for the calculations that 240 is the temperature I should get on the nichrome wire?
And related to this, where should I set the temperature sensor? Does it go inside the hot end or does it measure the barrel temperature?

- About extrusion: the way to extrude the plastic is simply melting it and letting it fall through the nozzle hole? I mean, I'm wondering if the hole through which the filament goes inside of the hot end was so tight that the movement of the filament generated pressure inside and that madethe melted plastic go out. Maybe this guess is just a fool idea but as I said I couldn't find this info anywhere sad smiley

- A bit to do with the previous one, how do you prevent the reflux of the melted plastic, i mean, how do you get the melted plastic not going up through the conduction where the filament comes in?


Just to make it clear, I'm not trying to make you work for me, I think these are basic questions and probably some of you won't answer because of that, but I couldn't find an aswer anywhere and I think you guys know a lot about this. I'm so excited with this 3D printing world and its enormous potential.

Thank you all in advance

Toalla

Toalla Wrote:
-------------------------------------------------------
> Hi,
>
> I'm quite new at this 3D printers world but I'm
> starting a project where I'll try to develop my
> won 3D printer arduino based.

Welcome to RepRap!

>
> I've been doing lots of research, reading articles
> and watching lots of videos, but most of the
> information refers to already-built printers, kits
> or upgrades for commercial printers so I actually
> miss some details abot how it works. Anyway I'm
> now specially centered on hot ends and extrusion
> and there are some base questions to which I can't
> find an answer, let's see:
>
> As far as I know a hot end is the device that
> heats the filament until it's melted. So, the
> filament is pushed by a stepper motor, it melts
> down in the hot end and it goes out through a
> nozzle. My questions are:
>
> - I can see everywhere "hot end temperatures"
> (like 240 C for ABS), can I assume that is the

240°C will melt most hot ends that use PEEK as the insulator.

> temperature on the inside surface of the hot end?
> or even further, if I were using nichrome wire
> around a barrel, could I assume for the
> calculations that 240 is the temperature I should
> get on the nichrome wire?
> And related to this, where should I set the
> temperature sensor? Does it go inside the hot end
> or does it measure the barrel temperature?
>

The temperature should be measured as close to the nozzle/melt pot as possible. The melt pot is preferably a very small region near the tip, where the temperature of the heater block melts the filament.

> - About extrusion: the way to extrude the plastic
> is simply melting it and letting it fall through
> the nozzle hole? I mean, I'm wondering if the hole
> through which the filament goes inside of the hot
> end was so tight that the movement of the filament
> generated pressure inside and that madethe melted
> plastic go out. Maybe this guess is just a fool
> idea but as I said I couldn't find this info
> anywhere sad smiley
>

The filament is 3mm in diameter. The nozzle opening is 0.35mm in diameter. The pressure is generated by pushing the solid filament into the melt pot. If the hot end design is good, the preasure is relesed through the nozzle. If the design is bad, it goes in the opposite direction, and you end up with a clogged insulator.

> - A bit to do with the previous one, how do you
> prevent the reflux of the melted plastic, i mean,
> how do you get the melted plastic not going up
> through the conduction where the filament comes
> in?
>

That's the trick, isn't it? Since the filament is still solid, and the opening of the hotend is always taking in more, any melt that tries to travel up gets cooler, and is pulled back down. This only works on good designs..

>
> Just to make it clear, I'm not trying to make you
> work for me, I think these are basic questions and
> probably some of you won't answer because of that,
> but I couldn't find an aswer anywhere and I think
> you guys know a lot about this. I'm so excited
> with this 3D printing world and its enormous
> potential.
>
> Thank you all in advance
>
> Toalla

Have a look at the J-Head hotend on the wiki pages. At this point, so many of us have tried it all, and the designs that have survived are pretty solid. Not that you should not experiment, but there are shoulders you can stand on

jcabrer Wrote:

> 240°C will melt most hot ends that use PEEK as
> the insulator.

Ok, I don't think I got the wrong info, I have read everywhere the working temperature for ABS extrusion is around 220-240 C and for PLA for example is around 180-220 C. If you say that temperature would melt hot ends using PEEK as the insulator, does it mean that those hot ends do not allow you to extrude ABS plastic? Or maybe I'm not understanding what you try to say, it's another option haha


> The temperature should be measured as close to the
> nozzle/melt pot as possible. The melt pot is
> preferably a very small region near the tip, where
> the temperature of the heater block melts the
> filament.


So, let's see if I'm getting it, melted plastic should literally flow over the temperature sensor?


> The filament is 3mm in diameter. The nozzle
> opening is 0.35mm in diameter. The pressure is
> generated by pushing the solid filament into the
> melt pot. If the hot end design is good, the
> preasure is relesed through the nozzle. If the
> design is bad, it goes in the opposite direction,
> and you end up with a clogged insulator.

Is there any mechanism to adjust the filament input or just a tight hole?

> That's the trick, isn't it? Since the filament is still solid, and the opening of the hotend is always taking in more, any melt that tries to travel up > > gets cooler, and is pulled back down. This only works on good designs..

Is that what is called "cold end"? So the extruder should have an upper cold part where melted plastic trying to reflux gets solid again, and a lower hot part, (melting pot) where it gets liquid and goes out through the nozzle, is that right?

> Have a
> look at the J-Head hotend on the wiki pages.
> At this point, so many of us have tried it all,
> and the designs that have survived are pretty
> solid. Not that you should not experiment, but
> there are shoulders you can stand on


I may end up buying one of those, most people has good opinions about them, but anyway I would like to understand how it works in order to solve future problems, and I'll probably try and build my own prototype.

Thank you again for your help, jcabrer, it is being really useful.

Toalla Wrote:
-------------------------------------------------------

> Ok, I don't think I got the wrong info, I have
> read everywhere the working temperature for ABS
> extrusion is around 220-240 C and for PLA for
> example is around 180-220 C. If you say that
> temperature would melt hot ends using PEEK as the
> insulator, does it mean that those hot ends do not
> allow you to extrude ABS plastic? Or maybe I'm not
> understanding what you try to say, it's another
> option haha
>

you will find that every supplier, and batches will have there own tempurature differences. some will be hotter and some will be cooler so it is next to impossible to give people a set temp, so the temps you have are the common ranges.

on that same note though you can print ABS with a hot end that uses PEEK has an insulator, it just means you cant print much higher than 230.


> So, let's see if I'm getting it, melted plastic
> should literally flow over the temperature
> sensor?
>

i have not seen that done yet, but i do not think that would be a good idea. it would add more points of failure, it is normally places close the the hot end, each design is a little different placement but i find that most are on the far side of the heater block from what ever you use for a heating element or on the nut used for the nozzle.

> Is there any mechanism to adjust the filament
> input or just a tight hole?
>
> > That's the trick, isn't it? Since the filament
> is still solid, and the opening of the hotend is
> always taking in more, any melt that tries to
> travel up > > gets cooler, and is pulled back
> down. This only works on good designs..
>
> Is that what is called "cold end"? So the extruder
> should have an upper cold part where melted
> plastic trying to reflux gets solid again, and a
> lower hot part, (melting pot) where it gets liquid
> and goes out through the nozzle, is that right?
>

no think more like a hot glue gun, they are not all that dissimilar, idealy your are pussing a solid into a chamber of fixed volume with 2 ways for the liquid to exit , the bigger hole where your filament should be a close fit so that the path of least resistance is out of the tip.

its when the path of least resistance is where your filament comes in when you end up with a lot of troubles.

> I may end up buying one of those, most people has
> good opinions about them, but anyway I would like
> to understand how it works in order to solve
> future problems, and I'll probably try and build
> my own prototype.
>
> Thank you again for your help, jcabrer, it is
> being really useful.
>
>

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[mike-mack.blogspot.com]

Thank you very much, dissidence, it's getting clearer and clearer, I'm definitely going to give it a try and if I kind of succeed I'll post the result on the forum.
Reading your tips I think the best and fastest thing I can do is just build a first device and apply the trial and error methode to modify it

if you ask me trial and error, is the best way to learn for a lot of things.

the fewer the pieces though the less trouble you will have, that much i can tell you. i am a big fan of the makergear hot ends, and a growing fan of the qu-bd hot ends. they have been good to me at least.

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[mike-mack.blogspot.com]