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3Apr/140 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:

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.


Hobbed bar, hyena v1.0

This is my take of a new hobbed bolt replacement :)

I call it the hyena, because hyenas have the strongest jaw of all mammals.
All teeth are cut individually:

Here is a comparison photo with one of my hobbed bolts:

The brass one is the new version:)
You mount it with a M8 nylock nut, so the width of your extruder does not matter.

Key advantage over the old version

  • It's machined from straight, round brass stock. Regular bolts often have large tolerances and are not entirely straight. The hyena is guaranteed to be straight.
  • Each tooth is individually machines, so there is no "orphan tooth". An orphan tooth is an incompletely cut tooth that occurs during hobbed bolt production with a tap, because the teeth of the tap do not match the diameter of the bolt while cutting. This is a problems because it's the spot where filament begins to slip. It tends to bite a small piece of plastic off the filament as it does not reach deep enough to grip. The next (normal) tooth continues eating into the filament, resulting a complete filament strip, and no printing. The hyena prevents this by making sure every tooth grips by the same amount.

Installing on a Wade style extruder

Some pictures, from the top:

Also when opened (please note the washers around the bearings!):

(Also take note the really useful and special M8 nut. It will be the subject of an another announcement:)

Im a technical guy, any drawings?

Here it is:

Enough talk, I want one!



When a compiler reach the state, when it can compiles itself, it's called self-hosting.
My Hot-end v3.0 reached that state, and more:-)

30Oct/10Off Hotend v3.0 dummy model

This is a dummy model of Hot-end v3.0 to get a feeling of the actual size. A real hot-end cant be printed using plastic:)

28Oct/10Off Hotend v3.0

This is a really big announcement.:-) The new hot-end has been born, and rocks!


Wade’s machined bolt version 1.3

This is only a small update about Wade's machined bolt manufacturing.


Heated bed kit v1.7 – laser cutted z-switch holder

This is a small upgrade of the heated bed kit compared to version 1.6.
I do believe I worked out all the caveats, and possible weak points of the design.