Arcol.hu hotend v4 adaptation for Rapman machines
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!
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.
For reference, see this v3 hotend assembly page.
Some exotic combination
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.
How to get it
Why have I decided to manufacture my own pulleys myself?
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).
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.
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
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.
Let's see what we have here.
I) T2.5@32 pulley
III) 608@T2.5 bearing
IV) 624@T2.5 bearing
V) High quality belt
Maybe you can source elsewhere, but this one is steel reinforced, and known to be working high quality belt.
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
Notice the non-existant or minimal clearance between the belt and pulley's teeth.
(For closeup picture, please refer to the bearing section.
This one could is not easily photographed because of the metal skirt)
High quality belts
You can get it here(TODO)
Bearings example assembly
In case of toothed 608 bearing:
It is really shiny, it is almost like having a brand new bike:)
Arcol.hu 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:
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.
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
(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?
This is a dummy model of Arcol.hu Hot-end v3.0 to get a feeling of the actual size. A real hot-end cant be printed using plastic:)