Arcol blog Just another RepRap weblog

3Apr/14Off hotend v4 for Rapman hotend v4 adaptation for Rapman machines

The assembled Rapman filament drive with the v4 hotend during extruding:

Get it here.


As you may be aware, back in 2010, the v3 version of the hotend (the PEEK based, so not the v4 all metal one),
was compatible mechanically and electrically with Rapman machines:

Starting from v4, the thermistor was intially switched to 104-GT2, which discontinued mechanical compatibility with the Rapman:

I then migrated to a Honeywell thermistor, which enabled me to leave out the fire cement, shown here:

These changes to the v4 hotend made it technically superior to the old one, and also way faster to assemble. However, it was neither mechanically nor electrically compatible with Rapman machines.

Recently, I have been approached by two people to get manufactured a fully compatible hotend for the Rapman. Two people are almost a crowd! :)

So with that in mind, I think I came up with a pretty good solution:

In detail

The length of the original v4 hotend was short by design,
however to maintain mechanical compatibility with the Rapman,
it needed a longer (73mm tall) hotend.
Pictured here is the assembled unit complete with nozzle, barrel and heatsink:

The new heatsink consists of two parts:
- The heatsink itself, which is 15.5mm longer than the standard one
- a disk, which goes on top of it, what you can mount on the Rapman machine using two M5 bolts.


The lower part of the hotend needs no modification, except it is
reverted back to the firecement version for using the 204-GT thermistor.

Summarizing the modification is basically a reworked heatsink and mounting plate.

I do hope it will serve well all the rapman users, who are still out there.

For reference, see this v3 hotend assembly page.

Some exotic combination

I will keep around the older heater block design which suits the
204-GT2 thermistor (and 104-GT2) because it is necessary for the Rapman.

The new and old heater blocks are compatible mechanically, so you can use the normal hotend with the older heater block if you need it for some reason.

Likewise you can get the Rapman version with the new heaterblock, if you have an exotic machine where this hotend suits better mechanically.


To date, I have only delivered two kits. Of these, one has
been installed and tested with very positive feedback.

Here is a quote from Rob:

I would like to add that the Hotend Unit you supplied is performing like a champion and has surpassed all of my expectations on its performance and reliability to date.
— Rob

How to get it

You have four variations to choose from:
- Assembled with 0.35mm nozzle
- Assembled with 0.5mm nozzle
- Unassembled with 0.35mm nozzle
- Unassembled with 0.5mm nozzle


High precision custom pulleys and belts

Why have I decided to manufacture my own pulleys myself?

Grab one here.

Spoiler alert:)

I) Not finished
The stock pulleys have only conical indentation at the end of the pulley, which acts as a starting point for drilling.


Also no M3 grubscrew either.
So basically you need to drill it on a lathe if you want precise work, and this directly affects the precision of the machine.
(Imagine an eccentric pulley).

II) Eccentric

If you make the pulley first, then you drill it even on a lathe, there is no way you can drill an absolutely concentric hole in the middle[1].
I tried to use a 32 teeth pulley once, we drilled on a lathe, and it was a tiny bit of eccentric hole, destroying the print quality immensely.
But if you drill the hole first, and you machine the outside while putting the workpiece onto a shaft, then it will be concentric, and now if you cut the teeth on the outside, then the endresult will be absolutely concentric.

In general, you always loose precision if you have to remove the workpiece and put back onto the lathe. There are solutions (4-jaw chuck, collet chuck) for the issue, but you start to tool yourself against this specific problem, which is expensive.

III) Low quality tooth profile

If you want to cut the teeth right, ie. within the tolerance specified in the DIN7721 standard,
then you need different cutting tool for the most popular teeth counts.
Some cheap sources, definietly save on cutting tools, having lower quality tooth profile.

IV) New possibilities

If I self-manufacture the pulleys, then it opens new possibilities, which was unimaginable before.
Just one picture to prove the point:

No more flipping the belts on the bearing end!

V) Less mechanical stress on the belts

With bigger diameter the belt turns on a bigger radius, that means less stress on the belt.
Also with toothed bearing (read below), you can forget about belt flipping.

The problem with belt flipping:

  • unnecessary stress on the belt, especially the steel cords inside. It may break, or delaminates over time.
  • aesthetically unpleasant
  • limited by the belt width (you can not flip a 20mm wide belt).

VI) Different (out of standard) width pulleys

It is just an idea now, but the possibility is there.
We can have 20mm wide pulley, if you are thinking in a really big (above 500mm) machine,
and you are affraid of belt stretch.

Product tour

Let's see what we have here.

I) T2.5@32 pulley

This pulley has 32 teeth, 5mm bore, M3 grubscrew ready to be inserted onto a motor shaft:

Available here.

II) T2.5@16 pulley
This pulley has 16 teeth, 5mm bore, M3 grubscrew ready to be inserted onto a motor shaft:

Available here.

III) 608@T2.5 bearing

This 608 bearing has a ring with T2.5 tooth profile, you can put it onto the other of the belt.
It solves the belt flipping problem.

Available here.

IV) 624@T2.5 bearing

This 624 bearing has a ring with T2.5 tooth profile.

Available here.

V) High quality belt

Maybe you can source elsewhere, but this one is steel reinforced, and known to be working high quality belt.

Available here.

Tolerance and precision

There is no backlash, if you have

  • good enough tooth profile (minimal clearance between the pulley's teeth and belt's one)
  • low weight carriage (under 1.5kg or 3 pounds for american readers:)
  • numerous teeth contact (16 teeth pulleys or more)
  • high enough tension, so the belt does not slip between the belt

Here is how the teeth look like:

And here is with belt applied.

Notice the non-existant or minimal clearance between the belt and pulley's teeth.

Standard flange

It has a flange and a degree between 8 - 20 degree according the DIN7721 standard.
Here is a picture:

Out-of-the-box experience

They are ready to go, you only need to put onto the motor shaft, even the M3 grubscrew is included.
No need hunting for lathe or sourcing small grubscrews or workaround with bigger M3 screws.

The belts fit well around the pulley.

(For closeup picture, please refer to the bearing section.
This one could is not easily photographed because of the metal skirt)

High quality belts

For your convenience, I have sourced high quality belts with steel cords inside.

You can get it here(TODO)

Bearings example assembly

In case of toothed 624 bearing:
M4 Bolt - (M4 washer) - M5 mudguard washer - M4 washer -
- (toothed) 624 bearing -
- M4 washer - M5 mudguard washer - (M4 washer) - machine

The M5 mudguard washer is enough in diameter:

In case of toothed 608 bearing:

M8 Bolt - special M8 washer of >30mm diameter - M8 washer -
- (toothed) 608 bearing -
- M8 washer - special M8 washer of >30mm diameter - machine

I used a special washer, which had 40mm diameter, maybe it is a bit overkill:

Update: I have manufactured special disks, which is only 0.5mm thick, so it does not wear of the belt's edge.
Obligatory picture:


Chrome beauty

Grab one here.

The chrome family:

Here is how the normal mini hyena v2.1 with 8mm bore looks like:

Here is how the mini hyena v2.1 looks chrome plated:

I think the normal hyena looks the most beautiful when chrome plated:

It is really shiny, it is almost like having a brand new bike:)

Here is a comparison photo between the mini hyenas:


Summary of 2012, 220% steam ahead

What a year. Read and remember the biggest moments of 2012.

And at the end get to know of a completely new product, the best way to finish a year.

Lets greet the new family member, the mini-hyena v2.0 and also regular hyena v2.0!

Achievements in 2012

Just a quick recap before we advance to the next big thing:) hotend v4 — 2012 January

Although the initial version of the v4 hotend went live at the end of 2011, many later improvements came this year. So it is a really 2012 product. Grab one here. hyena v1.0 — 2012 April

I started with v1.0, do you remember?:

M8 nut with M3 grubscrew — 2012 April


When a simple nylock M8 nut is not enough, and you need more torque.
Documentation here. Available here. hotend v4.0.5 — 2012 May

Bugfix release over v4.0. Announcement here.

Grooved 608 bearing — 2012 May

Tiny, but useful improvement. Original announcement here. mini hyena v1.0 — 2012 June


Discovering the need a reliable drive gear for direct drive mechanism, I launched the mini hyena campaign.

I gathered many feedbacks from this campaign, which helped to redesign the whole hyena family. See at the end of this article:) hotend v4.1.1 — 2012 October


I improved v4.0.5 more, and came out with v4.1.1:
It is not only bugfix (set screw), but also a real improvement (aluminium mounting) and aesthetic (black tubing) over v4.0.5 design.
Grab one here. hyena v1.1 — 2012 October


It is basically a usability improvement. Now you can counter-tighten with a 6mm wrench instead of a pliers.
For announcement, read here.
Grab one here.

Spring kit — 2012 November


Original announcement here. Grab one here.

Maglev fans — 2012 November


Maglev fans move more air with less noise; a small but nice improvement.
It is available for sale with the complete extruder (see next point).

Complete extruder — 2012 December


Original announcement here. Grab one here.

The Hyena family v2

The campaign helped me get the manufacturing done and gather much feedback.
Which kickstarted the design of v1's successor!

Asymmetric tooth profile - Hyena v2

To come up with this tooth profile it had taken countless hours and numerous versions.

Did you think the hyena was a great product? Then you'll think v2 is the best product ever!

The v2 outperforms v1 by 220%. That means at a given force where v1 has already slipped and chewed up your filament, v2 is still pushing it through happily!



For the tech-savvy out there, here is the drawing:

Unified size

One of the main discoveries from the campaign was
that the four different sizes did more confusion than good.

The conclusion is to make one size with either a 5mm or 8mm bore.
It makes everyone's life easier and one size fits all!

Here is a picture to demonstrate this handy property:

Regular hyena adjusted — Hyena v2.0

This news itself would deserve a separate article, as it is a huge milestone.
For v1.0 announcement, read here, and for v1.1 read here.


The shorter, the better

You don't need worry about the length of your motor shaft. Or particular extruder design,
because the mini hyena was designed to the shortest length possible: 10mm!

One size fits all

A picture worth a thousand words:)


Mini hyena fits on either 5mm or 8mm motor shafts.

Final look

When the extruder is properly set up the hyena accumulates absolutely no plastic chips over time.

Here is a photo after two weeks of continous printing:

If there are some chips inside, clean the Hyena with a needle not a file.
Never use heat especially not a blowtorch.

Printing achievements

I should compile an another article, where we are currently quality-wise, since I teamed up with a professional graphic artist (hey QNLaca!:)).

Until that article, here is a photo for the impatients:

Hall of fame

People, who made the mini hyena and also the v2 development possible:

  • Anonymous
  • dazed.dnc
  • Anonymous
  • atntias
  • Sefi1
  • fdefoy
  • harmonicity
  • hewball
  • houde.jeff
  • Anonymous
  • whosawhatsis
  • Intrinsicallysublime
  • bjoern5
  • contribute1334329857
  • cjmekeel
  • ckaosatom
  • scott.a.maher
  • wat_willy
  • raldrich
  • nop.head
  • device2003-kst
  • RobPovey
  • repraphd
  • justin.hawkins
  • Anonymous
  • contribute1338394611
  • vastempty
  • contribute1338413084
  • Anonymous
  • Inc0me
  • gary.s.hodgson
  • Anonymous
  • Anonymous
  • MattS
  • hoani.cross
  • boman22
  • lincomatic
  • Anonymous
  • colin22
  • m.feherpataky
  • DerekAnderson1
  • proto.user
  • Anonymous
  • SteveKelly
  • contribute1338109472
  • Pazu1978
  • AlessandroRanellucci
  • reprapdiscount
  • paranya2
  • Anonymous
  • Anonymous
  • labmat
  • maxinux
  • kurtis.burr
  • Anonymous
  • maik1
  • clem.taylor
  • Anonymous
  • Anonymous
  • JordanRoss
  • logxen
  • Anonymous
  • Anonymous
  • logxen
  • jax1000
  • reprapdiscount

It's Party-time! See you guys in 2013!:) Can't wait to show you my latest stuffs!:)
I change slightly the commenting policy. I will close the commenting after a week of the date of publishing to prevent spams leaking through.

But in all occasion, please prefer the mailing list.

After the above deadline, any further discussion can only happen on the mailing list, in this thread.


Recommended extruder setup


Grab the complete setup here.

Many people ask me what setup I am using with the v4 hotend,
or what setup I recommend for it.

I bit the bullet, and I wrote this detailed article.

I am always trying to push the envelop of 3D printing, therefore my machine
is evolving all the time, so you can expect more articles in the future:)

The extruder shown here will also be available as a kit through the website.

This recommendation is for 2012 december, although it could have been built since around 2012 march.

Partlist (with pictures) hotend v4.1.1:

Go grab one! or Grab the complete setup! hyena v1.1:

Go grab one! or Grab the complete setup!

M8 nut with M3 grubscrew:

Go grab one! or Grab the complete setup! spring kit:

Go grab one! or Grab the complete setup!

40mm fan:
Are you wondering why is a cap there?: Maglev carriage fan

Wade's accessible extruder body:

Carriage with 2 fan holders:

Satchet of nuts and bolts:

608 bearings and linear bearings (LM08UU):

Just to see it in perspective:)

Downloading the .stl file of the RP parts

All of the RP parts, are from thingiverse.
However I have modified almost all of them. I will publish one .stl file per
week on thingiverse, referring back to the original thing and its author.

Assembly of the carriage

Here is the carriage one more time:

The linear bearings goes in there:

The two fans on the sides, and it looks like this when mounted on a machine:
(Note: There is one bar clamp missing from the above picture)

The modell of this print is available on thingiverse, as thing:39923. It is basically a touchup of thing:15534, which is based on thing:9869.


This is the idler of the Wade extruder pusher:

It has an integrated guide, so you dont need the grooved 608 bearing,
to guide the filament, its mere cost saving.
You can still have the grooved 608 bearing, it does not make things worse, this idler just duplicates the grooved 608 bearing feature.

The modell of this print is available on thingiverse, as thing:39933. It is basically a touchup of thing:17030 and thing:6703.

I have RP parts available in three different colors: white, green and black.
Here is a comparison between green and white print:


Here is the gears I use:

You may be wondering why I am not using herringbone gears.
Herringbone gears run a little quiter, and have a tiny bit less backlash.
Also they can handle higher torque.

However it does not affect print quality.
The filament has a backlash due to its inertia, and we compensate
for backlash anyway. It has the same number of teeth, so no additional
resolution either (not that we need it).

But the main reason is that it is more troublesome to print out, for no real
advantage, so I kept the traditional spur gears. You can print a
herringbone if you wish as an upgrade.

Wade pusher (extruder upper body)

Here we go:

It is a modified Accessible Wade extruder, mainly the holes were adjusted.
It is more accurate and compatible with
v4 hotend.

Here is how the gears, idler and wade upper body will come together:

The complete setup

The complete extruder assembled with carriage. Everything mounted:

You can see the setup is standing on two M8 nuts, so the
hotend is lower by just enough distance then the two fans.
It is optimised for the minimum height, so you have the
maximum printing height possible*.

Here are some more pictures, it is kind of rotating:)


You could have build this extruder setup from about february of this year (2012).
If someone would have published this extruder setup back in time, it
would have saved me some unnecessary circles.
So I hope you (dear Reader) find this article equally useful,
what I would have found it, if it was existed back then.

Printing quality

If you want to check what is possible
with our v4
hotend in regard of printing quality, or you want a trouble free
extruder setup, then go get one!

As a remainder, here it is the wade pusher printed in white:
(the white is the easiest to photograph, every irregularities are shown)

Im fairly happy with the overall printing quality, you can see it as
our current state of the art at 0.3mm layer height.

No worries, even finer layer height is possible, so it is not the
limit of what v4 is capable of.


Grab the complete setup here.

I think Im able to print one full set per week, and for start I have
3 full sets. I know it is limited, but it is not intended for general
public, just for the quality enthusiastic and those who want
a working printer first and a DIY machine second.

I have some leftover pictures, which would be too bad to miss out:)

And even moar:

I change slightly the commenting policy. I will close the commenting after a week of the date of publishing to prevent spams leaking through.

But in all occasion, please prefer the mailing list.

After the above deadline, any further discussion can only happen on the mailing list, in this thread.

30Oct/12Off hotend v4.1.1.


For previous announcement please read here:

The v4.1.1 version

Im really proud to announce hotend v4.1.1:

In a nutshell:
- v4.1. - aluminium mounting plate (that also means integrated setscrew in the heatsink)
- v4.1.1 - firesleeve

Aluminium mounting plate (v4.1.)

I replaced the wood mounting plate with an aluminium one.

Just to recall here is how the v4.0.5 looked like:

Here is the v4.1:

I also added an M3 setscrew, to fix the heatsink to the mounting plate
(prevent rotating the whole hotend at high speed).

Also here is how the hotend looks after 6 months of printing:

So the firecement is quite good solution, once it is applied.

Firesleeve added (v4.1.1)

To prevent skin burn, protect heater block against fan blow, and last but not least looks awesome:

Machine compatibility

This hotend is designed for reprap machines (or compatible).
However I had success reports from customers using in 24VDC system, like R2C2 electronics (you need different resistor, so definietly say it before purchase).

I would be really interested how others have mounted or adapted this hotend for their machine,
like or

If you happen to have a machine like the above, and you want assistance,
just drop me an email through preorder(at-arcoldothu.

Go grab one:

I closed down the commenting on this webpage due to the enormous number of penis enlargement suggestions.

If you have any thoughts to share about this article, please discuss it on's mailing list,
in this thread.


Arcol Hyena v1.1

Available at:

History (v1.0)

For previous v1.0 announcement, read here:
and here:

V1.1 update

This is a minor, but really handy upgrade to hyena.

At one end it has 6mm flats for wrenches. So no more pliers to holding while putting the big gear onto the shaft.

This is how it should be mounted (flat end is the opposite one from big gear):

Here is a closeup of the two flat sides:

Here is how you should put the big gear onto the hyena:

Also here it is mounted on the extruder pusher:

(Note the M8 nut with M3 grubscrew! It is *really* useful)

M8 nut with M3 grubscrew:

I closed down the commenting on this webpage due to the enormous number of penis enlargement suggestions.

If you have any thoughts to share about this article, please discuss it on's mailing list,
in this thread.

17Oct/12Off spring kit

Available at:

This is a simple spring kit for the extruder pusher:

Many people have trouble finding the right spring for the job, so
I decided I will offer the exact same springs, that I use on my own machine.
I settled to this spring after trying out more then 20 different springs.

The ideal spring is small, stiff, but not too hard to compress,
so the hobbed bar (hyena) does not bite into the filament instantly.

Also when you change the filament, the bolt is long enough so you do
not need to take it out completely from the extruder pusher.

Curious enough, how it looks mounted?:), here we go:

Go grab one!:

I closed down the commenting on this webpage due to the enormous number of penis enlargement suggestions.

If you have any thoughts to share about this article, please discuss it on's mailing list,
in this thread.


New: Grooved 608 bearings

This is the new 608 grooved bearing:

It has an awesome half circle groove which is a perfect fit for the filament.
I use a normal 608 bearing, so it fits to a Wade style filament pusher exactly, like
the Greg's accessible extruder body (thing:8252). Here is a closeup picture:

Here is how the filament would look like on the bearing:

And also a picture with the hyena:

Oh wait, I can do a better photo, to see from the front (notice the match for frame of reference):

Why is it an awesome thing to have?

  • It prevents filament twisting
  • It is a guide in itself, Accessible Greg's extruder, needs one I believe, at least for me its needed. (accidents happen:-(

Im collecting ideas here. Im recently trying out many methods to raise funds to manufacture the newest gadget for 3D printing world:)

Well, this small improvement may not deserve a full campaign, like the awesome mini hyena, but still what do you think what would be an adequate price for it?

If you have a thought about pricing, or more what price is it worth for you, just put it in the comment. If we can agree on a sane pricing, I will list at that price on the webshop:)

Lets do it folks!

Some of you were wondering how much flesh rest at the bottom of the groove.
So I destroyed one for ya:)

And here is a better view from the front:

Im not worried about wall thickness here, it is imho pretty strong still.
If you have any other question just shoot it in the comments:)

14May/12Off hotend v4.0.5 v4.0 hot-end for 3.0mm filament (works also for 1.75mm filament too).

It has been a long time since I announced v3.0.

The new features:

  • - Hot-zone is completely metal.
  • - high temp extrusion should be possible, like pp, hdpe, plexi, polycarbonate, nylon (hopefully, this will be confirmed within a month)
  • - shorter, more compact, a comparison photo between v3.0 and v4.0:
  • - easier to assemble
  • - reworked nozzle
  • - laping for wrenches on nozzle, on stainless steel, heatsink
  • - built for easy maintenance
  • - self cleaning (you can remove the hardened plastic using two wrenches:)
  • - built with dual extruder in mind
  • - mounting compatibility for the average/stock reprap hotends
  • - 100k thermistor (which seems to be a more common preference)

For assembly instructions please read here:

Regressions/future adaptations:
Dropped compatibility for Rapman, Makerbot. A new mounting needs to be designed for these machines.
For rapman a 200k thermistor also needs to be sourced to be electrically compatible.