Merlin Hotend

Hi all,
i just created a new home for all information around the Merlin Hotend i developed
Merlin Hotend
It's still a bit early but it already contains a construction description and a couple of print tests i did.
Cheers
Björn

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Interesting - keep it up!
From my limited experience the long nozzle (actually more like longer distance between the heater and the mechanism pushing the filament)) and the cooling is to stop jamming with PLA. The issue is called "heat creep". Have you tried PLA, or something else that softens at ~80°C?
Of course if you don't plan to use PLA (or somehow get it to work with PLA), it looks like a great little hot end that you could pair with a small form factor extruder.

The Makerbot Replicator 2 and 2X use a relatively short hot end as well, although the 2X can't print PLA reliably and the 2 (not X) prints PLA with some relatively serious cooling in the form of a size-mounted blower fan.

While i myself don't print PLA, several others do. They do use a small fan to cool it, but from what i know mostly for higher precision prints, it shouldn't clog anyway.

Srek,
What is max extruder e-feed rate for ABS when extruding in the air ( mm/min)?

Edited 1 time(s). Last edit at 10/14/2013 11:49AM by karabas.

karabas Wrote:
-------------------------------------------------------
> Srek,
> What is max extruder e-feed rate for ABS when
> extruding in the air ( mm/min)?

Good question, but sadly one i can't answer very soon since i just accidentally destroyed the USB port of the controller. I can still print from SD card but it will take a while until i can control the machine directly again.
I do have an older video online that shows an early version of the Merlin Nozzle at speed
[www.youtube.com]

Sorry
Björn

every hot end should have a rating of how much force it takes to extrude filament, continuously, after retraction and after it has been sitting hot, and after its been sitting cold.

aduy Wrote:
-------------------------------------------------------
> every hot end should have a rating of how much
> force it takes to extrude filament, continuously,
> after retraction and after it has been sitting
> hot, and after its been sitting cold.

Good idea, any idea on how to do the measurement?

One of the things that brought me to the point of developing my own hotend was that a lot of force was needed to push filament in the then existing hotends. It was so bad that i started designing the extruder in a way that you could easily clean the hobbed bolt from filament powder that got scrapped of. With the Merlin hotend this is a non issue, i only ever get damaged filament when it is out of specs and clogs the extruder, like it happened lately with oval t-glase i encountered.

Edited 1 time(s). Last edit at 10/15/2013 08:02AM by Srek.

Here's a method of measuring extrusion effort. It's still in it's early stages of design but the electronics and firmware is now available for everybody. The graphing software is being prepared for release, however, force measurements can be view through the Arduino IDE serial monitor.

Airtripper Extruder Filament Force Sensor:
Arduino Load Cell Circuit & Sketch for Calibration Test [airtripper.com]
Design & 3D Print [airtripper.com]
Introduction [airtripper.com]


Srek Wrote:
-------------------------------------------------------
> aduy Wrote:
> --------------------------------------------------
> -----
> > every hot end should have a rating of how much
> > force it takes to extrude filament,
> continuously,
> > after retraction and after it has been sitting
> > hot, and after its been sitting cold.
>
> Good idea, any idea on how to do the measurement?
>
> One of the things that brought me to the point of
> developing my own hotend was that a lot of force
> was needed to push filament in the then existing
> hotends. It was so bad that i started designing
> the extruder in a way that you could easily clean
> the hobbed bolt from filament powder that got
> scrapped of. With the Merlin hotend this is a non
> issue, i only ever get damaged filament when it is
> out of specs and clogs the extruder, like it
> happened lately with oval t-glase i encountered.

Edited 1 time(s). Last edit at 10/15/2013 11:33PM by Airtripper.

---

Blog - [airtripper.com]
Extrude Filament Force Sensor - [airtripper.com]

Nice idea. It's limited to bowden setups though. I'll see if i can build that as a pure testplatform, it would be nice to get a curve that puts nozzle temperature in relation to force needed as well.

Some more updates, the technical specs are now available
[merlin-hotend.de]

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

nice this is exactly what i was talking about, now maybe someone can make a poll or something where we can put how much force it takes to extrude for each extruder.

Quote
Airtripper
Here's a method of measuring extrusion effort. It's still in it's early stages of design but the electronics and firmware is now available for everybody. The graphing software is being prepared for release, however, force measurements can be view through the Arduino IDE serial monitor.

Airtripper Extruder Filament Force Sensor:
Arduino Load Cell Circuit & Sketch for Calibration Test [airtripper.com]
Design & 3D Print [airtripper.com]
Introduction [airtripper.com]


Srek Wrote:
-------------------------------------------------------
> aduy Wrote:
> --------------------------------------------------
> -----
> > every hot end should have a rating of how much
> > force it takes to extrude filament,
> continuously,
> > after retraction and after it has been sitting
> > hot, and after its been sitting cold.
>
> Good idea, any idea on how to do the measurement?
>
> One of the things that brought me to the point of
> developing my own hotend was that a lot of force
> was needed to push filament in the then existing
> hotends. It was so bad that i started designing
> the extruder in a way that you could easily clean
> the hobbed bolt from filament powder that got
> scrapped of. With the Merlin hotend this is a non
> issue, i only ever get damaged filament when it is
> out of specs and clogs the extruder, like it
> happened lately with oval t-glase i encountered.

I Really like the idea!

I'll post some prints as soon as I get it from RRD.

---

ePoxi

---

My designs @Thingiverse - RepRap Argentina Users Group Wiki - #RepRap.AR en Freenode WebChat - Grupo RepRap Argentina @Facebook

Question for Bjorn:

I have installed a Bulldog XL from RepRapDiscount onto my Mendel Prusa, with the Merlin hotend. This replaces the previous Wade's extruder, with which I'd got some OK prints.

Does the Merlin hot end benefit from the cooling fan supplied with the Bulldog?

The reason I ask is that I have been trying to commission the Bulldog and have not yet achieved reliable extrusion.

It might be the ABS filament, which is on the high end of the diameter tolerance at a shade over 3mm on one axis and a shade under on the other. If I move it by hand into the extrusion channel, it moves smoothly, though needs to be pushed (which the Bulldog should be good at right?).

I also note from your Merlin website that you recommend reaming the PTFE tube out - do you have any idea if RRD do that?

Thanks, and best wishes, Chris.

Verify that the filament feeds through the nozzle by hand.
If it's difficult to push the filament through the nozzle by hand it might be clogged. If it feeds easily then look at the extruder.
Don't trouble shoot with black filament, as it could have cheap fillers added.
It's typically better to have a fan on the cold end as it reduces the glass transition temperature length, which reduces the force to push the filament through the barrel.

[forums.reprap.org]

I don't know if they ream the PTFE, but i doubt it. Afair the hotend is only loosely assembled and reaming should be done after it has been screwed tight..
As for the fan, with ABS i usually don't need it, but i see no disadvantage in using it all the time.

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Hey
I drilled the PTFE tube after tightening the hotend together, this has resulted in the tube having a diameter that is slightly bigger than 1.8mm

The hotend prints 1.75mm PLA with a Bowden system setup.

Cooling is done with a hotend holder I designed myself, but as you have a bulldog, you don't need mine!

Just make sure that with ABS printing, the air doesn't move over the print surface, as it makes your prints almost sure to warp and 'plop' off the bed.

What do you mean with 'ok' results?

Thanks for the help everyone! I went through a number of the diagnostics suggested + one more.

@A2 - I couldn't push it through by hand, but I struggle to push it through that extruder even when the whole hot end is off, of which more, further down. As it happened it was blocked. I swapped back to the Wade extruder, in which it's easy to push the filament by hand. I couldn't get a reliable run through, and took your advice to switch from black. I substited a likely good grade of white filament, and it's a lot better (though there were problems due, I think, to the hobbed bolt in the Wade).

I have tried the fan on the Merlin briefly, but I think it cools the heater more than the PEEK barrel.

@Srek - thanks for your comments. The Merlin hot end seemed to have become blocked, so I left it soaking in acetone for a couple of days, and cleaned it out. Unfortunately, I can not unscrew the brass nozzle from the PEEK - rather, I'm reluctant to exercise sufficient brutality, for fear of mashing up the nozzle and barrel. The brass nozzle doesn't seem to be completely screwed in, so I'm *hoping* it's screwed down snug to the PTFE. At the top end, the PTFE sits a bit proud of the PEEK barrel, so it screws up tight to the alu slot mounting bush.

@Ohmarinus - my 3mm ABS filament seems to fit easily in the PTFE, so I'm reluctant to drill it out. There are other points on the filament path which are tighter. The brass bush as the filament exits the drive chamber, is particularly tight, and the alu slot mounting bush is tighter than the PTFE - I think this is exacerbated by the filament getting a set in it if it's been sat on the hobbed wheel too long. The current white filament is 3.06mm max, so should be OK.

So currently, it's still jamming, though not quite as frequently.

Chances are the connection between brass and Teflon inlay is tight. If you think it is neccessary to open the hotend try to heat it up to normal operational temperature beforehand.

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

OK so looking to set up one of these hot ends, want a recommendation on which extruder design people may of had some success with? currently using a modified Gregs Wade with a cheap J-Head on a Prusa I3 Remake, and planning the upgrade.

Ah yes, I'm using the Airtripper bowden extruder, had to make small changes and will even redo the design myself because I had one small problem with the grub screw of the MK8 gear sticking out too much that it would push against the idler bearing and push the idler away causing slippage of the filament.

In theory the Merlin will work with ALL J-head compatible extruders

As a follow-up to my last mail: I bought a new batch of black abs filament from 3Dfilaprint, and it's going fine; so I think a lot of my initial problems were filament quality. I have to disassemble some of the Bulldog XL drive to get new filament in, but once it's going, it seems pretty happy.

I aim to get some better (i.e. deeper channel) hobbed bolts to see if I can get better performance from my Wade: they're not expensive.

@Matticus: what sort of improvement do you want on your existing setup?

This might be a stupid question, but why isn't the PEEK part getting too hot over time? Does PEEK radiate enough heat so that it keeps up with the thermal conductivity? Why doesn't it need active cooling? Also why doesn't the PTFE tube melt if it's in direct connection with the brass part? I guess these are general questions as the J-Head uses the same design, but I'm curious.

Another question about a bowden setup, wouldn't it be best to use a long PTFE tube, thread it one one end and screw it directly into the PEEK part? Wouldn't that eliminate the need for any push fittings?

Thank you Srek for sharing your nice design! Utilizing airbrush nozzles seems like a very good idea.

The M10 thread on the PEEK increases the surface area sufficiently for the hotend to radiate the heat. Depending on the material you are printing you do need active cooling, especially PLA works better with cooling.
The upper part of the brass part does not get nearly as hot as the lower end, while the PTFE does get a bit soft, it will not melt. The cooling done by transfering heat to the PEEK part is enough (up to certain temperatures, i don't recommend using the Merlin hotend above 250C° and then only with cooling).

Have you ever tried to thread a 4mm PTFE tube?
I have, it's a bloody nuisance. It is certainly possible for industrial machining, but not for me. Also due to the PTFE beeing so frictionless it would easily unscrew itself. That is one of the reasons why the 6mm PTFE tube in the hotend hast to be screwed in so tight. Only the deformation achieved by that will keep it in place. The other reason is that it needs to be tight to seal the gap between PTFE and brass.
If you check my g+ postings or youtube videos you can see that i am currently designing a bowden extruder that does not need pushfits, so far it works nice
[www.youtube.com]

As for the airbrush nozzle, i got that idea from Chri when he visited Hackerspace FFM, just like many others did help me on this over time. The afaik really unique features are the threaded inliner and the outer threading for cooling.

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Thanks for the explanation! I guess I should have looked up the melting temperature of PTFE, it's actually 326°C so of course it should be fine.

And I didn't figure that the normal bowden tube is 4mm thick, not 6mm like the lining in the merlin hotend. I think the E3D V6 uses a continuous 4mm bowden tube from extruder to heat break, and use a special coupling to hold the tube in place. I don't know if a "through and though" bowden tube is really needed, but it wouldn't hurt.
I guess I could try to retrofit this idea by printing a clamp or something to hold the ptfe tube and hotend. But you'd need another lining tube of 4mm inner diameter, to fit the 4mm tube inside the peek element, or have to drill out the existing 6mm threaded tube. Can you glue together PTFE with heat resistant glue?

I hope I'm making sense, just thinking out loud here I'm just assembling my first printer and looking at my J-Head clone where you have PTFE lining, a grub screw, then a press fitting, and think that can't be a good setup. I'll follow your plus pages for more updates!

PS: Could this pneumatic fitting work to pass through and hold in place a 4mm PTFE tube? It has a M6 outer threading and 4mm inner diameter: [www.conrad.de]

Edited 1 time(s). Last edit at 06/23/2014 09:23AM by Dejay.

I created a Wiki page for the Merlin hotend. Its pretty much a copy of Sreks blog page, so just FYI or if you like to participate.

---

LG

Jonas

hey i love the merlin hotend design !
it's way cheaper (from where i am located) to get a merlin hotend.
with the added advantage of the screw on nozle.

I don't want to complain!
but have you taken a look at the E3D and how they fasten the ntc ?
wouldn't that be possible with a merlin hotend?
also i don't know if it's a big issue though. but the topend of the merlin hotend. (where the filament enters)
if it's hole were a bit cone shaped could guide the filament into the right direction?

anyway i am in no possition to complain though
i haven't even used the hotend yet!.
(i am kinda scared to) due to the nozle being to fragile

besides what i have seen and heard so far, is that it's a pretty good nozle

Greetings,
Duality

Personally i use heat resistent glue or silicon to mount the thermistor.
The top opening of the hotend is only slightly tapered so there is no rim. I did not put a bigger cone in there by intention, it would have adverse effects when printing very soft materials like Ninjaflex or FPE.
I hope you have fun and good results with your Merlin.
Cheers
Björn

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

i see thanks for the reply !

i have encountered the problem of the filament not going into the hotend though. so i gues i'll have to make my own cone in it
it's aluminium ?

Greetings,
Duality

You are talking about the j-head adapter? Yes, that is aluminum. I was actually talking about the PTFE part
The J-Head adapter is something reprapdiscount added to the package to make the hotend compatible to many extruders.

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]