Remaking the Vertex K8400 Printhead

The original printhead for the Velleman Vertex K8400 3D printer is simply not a good design. I have upgraded problematic parts of the 3d printer by re-designing the printhead and changing belts and pulleys. This article describes why and how i performed this upgrade.

Problem 1: The ‘PEEK isolator’.

This is a plastic heat sink, that will not dissipate enough heat, which causes several problems during printing.

This is due to a simple fact; PEEK is good for many things, but thermal conductivity is not one of them. In fact, the average thermal conductivity for PEEK material is around 0.29 W/mK. Where as common steel, used in most common 3d printer hotends, is around 50 W/mK, 172 times better at releasing the heat – which is the purpose of the heat sink. PEEK’s thermal conductivity will increase linearly with rising temperature, but that is not relevant, as the heat-sinks temperature should stay as low as possible.
So not only is PEEK not suited as a heatsink, Vellemans heat-sink design is also very short, which causes it to heat up very quickly.
This has been documented many times on various forums, with different issues ranging from highly frequent clogging, to heat-sinks almost melting down.
Billedresultat for vertex isolator burnedBilledresultat for k8400 clogged

So it s a no brainer; the orignal Vertex K8400 printhead is a poor design. A new is needed. I choose the E3D Lite6, as it fit my needs exactly; It has a steel heatsink with active cooling, and as i only print PLA, the ‘lite’ (Max 240 degrees C) is the cheapest option that fulfills my needs.

Installing the E3D hotend on the Vertex K8400 requires a new mountplate. I designed a mountplate which could hold the hotend and a 20mm fan. I had this plate milled in aluminium, the hotend fixated with a 4mm bolt. The design causes no loss of print-space in XY axis, but a loss of 5mm in the z-axis.
I removed the original ‘Excluder board’. It’s only job was to offer easier mounting of wires and flashing red lights. Completely useless. Instead i hooked up the E3D active heatsink cooling fan to pin ‘Fan1’, and the print-cooler was coupled with the mainboard cooling-fan in pin ‘Fan2’.

I set ‘Fan2’ to activate when temperature was above 50 degrees C. This makes sure than the active heatsink cooling fan will turn back on if the the mainboard restarts or temporarily looses power, keeping the heat from creeping up the hotend.


Problem 2: The pulleys of madness

The Vertex K8400 is borne with GT2.5 system belts and pulleys – these belts are less common in cnc supply stores than the GT2 system, but they are obtainable. What is less common, is the pulleys, which has 19 teeth.
These are only available through Velleman Vertex 3D printer parts suppliers. Even if you find one of these rare suppliers, the price for one pulley is 18 Euros – just about 5 times more expensive than standard 3D printer pulleys. On top of the shitpie, is the brown-cherry fact that these pulleys has a 1.5 mm thread for fixation on the rods that is removed when tightened properly.

Why anyone would use 19T pulleys is beyond me. I have pondered about this for quite some time, but i can not figure it out.
It is pure madness. Let me explain why;
The standard NEMA17 motors used by most 3D printers, including the Vertex K8400, have a 1.8 degree step angle. The motor turns circular, 360 degrees, which means the stepper motor takes 200 steps to make a complete 360 degree turn. 200 steps, an even easy number. These steps are then geared up by the pulleys pulling the belts, which moves the printhead.
This is where Velleman chose the odd 19T pulleys.

A stepper motor with a 1.8 step angle, turning 19T pulleys on GT2.5 belts, takes 134.74 steps per mm. An uneven number.

Though these steps are absolute, thus only accumulates in the single g-code line – they still present a fundamental error, as the stepper motor  can not take less than 1.0 step, the decimals are lost, causing small deviations from the sliced model.

My solution was to swap out all the pulleys to 20 tooth pulleys, and in the same maneuver i switched belts and pulleys to the more commonly available and cheaper GT2 system.

A stepper motor with a 1.8 step angle, turning 20T pulleys on GT2 belts, takes 160 steps per mm. An even easy number.

Firmware changes:

//For Gt20 belts and pulleys//

#define DEFAULT_AXIS_STEPS_PER_UNIT {160,160,4266.66,200} //
//For setting Fan 2 to run board cooling+active nozzle cooling above 50 degree c //

//#define EXTRUDER_2_AUTO_FAN_PIN -1
#define EXTRUDER_AUTO_FAN_SPEED 255 // == full speed

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