Best hot end?

Hi all,

I have a multi-purpose 3-axis robotic workcell, that I need to add an extruder head to, in order to make it a 3D printer. I've been working with some high-schoolers who have built the machine...
Workcell
PnP config

They also built an extruder feed mechanism (pics overdue), and we started engineering a hot end using chassis-mount power resistors for the heater (similar to the plastruder mk5), but it seems that's a very bad thing to do -- as even within max temp spec externally, these resistors can fail since the internal core temp can be much higher. And apparently they can fail violently. So I'm looking for a new hot end, but confused about all the versions/variations/tweaks etc. Of all the designs, which one really works best? "Best" meaning getting the finest extrusion, and reliable.

At this point, I'm leaning towards buying the parts and assembling it, or perhaps buying the hot end already-built.

Thanks,
-Neil.

many work well,

lots of people like the makergear ones, arcol.hu and copies, jhead and others.

I have a few things I commonly say on the subject that I think work well as general rules:

1. Don't rely on peek or ptfe threads for strength, this doesn;t mean you can;t have them just support the pressure with something else.
2. keep everything above the nozzle cool, heatsinks and/or fans help.
3. don't get too hung up in the mounting details, I mount them all with picture hanging wire, any shape to and drive.
4. be careful in your wiring, make sure it won't come loose and you thermistor won't pop out. make real sure wires are well insulated.

as your 1st extruder I recommend against making your own from scratch. It's good to become familiar with how they should work before building your own.

Threads in PEEK work fine for me.

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[www.hydraraptor.blogspot.com]

Peek works fine with high pessure, but you must know how... and you dont need any support...

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Mfg
Wolfgang

Aller Anfang war schwer - Wolfstrap

Reprap-fab.org

Erfahrungen kann man leider schlecht weiter geben, die muss man selber machen.

I know we have been around a few times on this, and I know people got it to work... I completely stripped out peek threads on an arcol hot end, they were very tight fitting, I got them too hot and there was a lot of pressure... not the fault of the hot end design really but something I'd like others to learn from... my take is, if you add external support you haven't hurt anything, you've only added to the reliability. It doesn't limit what hot end you can use, anyone can get a fender washer, cut notches into it and run picture hanging wire for support. Lately I also drill holes in the fender washer and run the insulated thermistor and resistor wires through those hold and it keep them in place more reliably. I know these things are optional, but due to their low cost and ease they are good things to know, especially if you've had problems in that area.

here's a picture of what im talking about. I've become neater with it since, but it gets the idea across. [suddendevelopment.com]
this solution costs less than $1

Imo threads in ptfe could work too, but M10 minimum, and M12 - M14 - M16 for the best.
Even so, its still probably better if one doesnt rely on threads for support.

I tried an M10 external thread with PTFE and it didn't last long enough to do the first layer.

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[www.hydraraptor.blogspot.com]

PTFE you can forget, I have a graveyard full of such hot ends.
PEEK with the PEEK threaded into the metal hot end with a PTFE tube inside works well.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

nophead Wrote:
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> I tried an M10 external thread with PTFE and it
> didn't last long enough to do the first layer.

Very interesting to me. I used same on ptfe and one of them at least so far has gone through 2x2.3 kg rolls of filament and changed like 3 aluminium blocks, and over 12+ brass nozzles with slightly different shapes i could do. Still works, except once when tried a new block i mis-turned it while screwing and ruined a good part of threads. To repair i applied alot of ptfe tape mixed with layers of rtv silicone to harden it, and fixed it so it still works, just dunno if i unscrew it now if it will be usable after.

Might be different grades of ptfe perhaps. I think there is quite a big variety of sorts on the market. This could be main difference.

Edit:
Also maybe the shape can do something aswell, i use a slow slope which starts a few mm away from the thread end. I also only tighten the block by hand, never with the wrench, and even by hand not too tight. A picture in the other thread shows a thread which ends abruptly. Prone to get fractured when assembling, simply by tightening it. And maybe with that shape, at temperature, the dilatation pulls the metal away more, so it breaks it. Dunno if it happens like that or not, but it might explain the instant breaking it. Otherwise if it would be pure ptfe failure at least should last for some minimal time, and should show signs of fatigue, like ptfe turning into cheese, basic signs of deformation, that sort of looks instead of pure severe "clean" sectioning it.

Edited 3 time(s). Last edit at 10/27/2011 11:55AM by NoobMan.

I have a hot end from maker gear.
wades mounting with the laser cut wood holding the nozzle into the hot end with screws on the sides
Go here:
hot end
The hot end has a grove it sits in.
And there is a hole in the motor and feeder part that the nozzle fits into.
It doesnt budge.
2 but getting close to 3 lbs printed. just make sure everything is tight.
Hobbed bolt cleaned once. I recommend using a piece of all thread and dremel notches across it.
I have not had many issues with this extruder.
For me a must get for beginners. or really anyone that is having issue with there extruder.
Ill stick with Wades for a while
-Erik

I have had hot ends push apart in my early days, but this was due to running the extruder at too low a temperature. Low temperatures raise the extrusion forces a lot and hence tend to push the hot ends off. This probably explains why there is some disagreement as to the threads in ptfe / peek debate, people run different temperatures and build at different speeds.

I have used a plywood plate (about 6mm) to bolt into my extruder and then 3 tie bars down to the washer above the nozzle. It works really well in my opinion, so on my new design I would go for wood and tie bar design again, cheap, easily worked and a good insulator.

Heres a prebuilt one if you just want to fit and go.....Quite dear though.
Rapman Hot End

When you have external support like that then you can also use PTFE (teflon).
The discussion was about PEEK vs PTFE threaded into a hotend with no other external support.
PTFE just does not hold up, not even for PLA and certainly not for ABS.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Interesting read, thanks everyone. What I would like to ask is your opinion on Aluminium nozzles versus brass. Any thoughts appreciated.

i run a makergear topend on my orca3
and will prolly never go back

and is that ally or brass?

tony woollacott Wrote:
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> and is that ally or brass?

It's brass. Brass conducts heat a bit better than aluminum, but using aluminum for the hot end will work just fine.

Edit: It seems I was thinking copper vs. aluminum rather than brass. Aluminum is more conductive than brass, but less so than copper. I stand corrected.

Edited 1 time(s). Last edit at 03/24/2012 12:37AM by NewPerfection.

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Actually, aluminum is a better conductor than brass by 30-50%

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www.Fablicator.com

Thermal conductivity coefiecients
Aluminum - 250
Brass - 109
PTFE - 0.25