Before we explain more about the upkeep of your HeatCore Unibody (or its repair, where required), we are briefly going to provide more details on the various types of hot-ends available on the 3D plastic extrusion printing market.

The ideal hot-end

The ideal hot-end (imaginary) would have the following features:

• The hot-end tube and the filament would have the same inner diameters, to ensure perfect transfer of force.
• There would be no friction between the filament and the inner walls of the hot-end to make extrusion easier.
• Fluidisation temperature would be reached by the filament in the heating block (usually around 200ºC) and upwards thermal cut-off would exist to prevent heat from spreading towards the extruder.

However, these features are not available for a number of reasons:

• Both the filament and the inner hot-end tube have diameter tolerances and, therefore, a space must be left between both diameters to prevent jamming. For instance, a hot-end for a filament of 1.75 mm usually has an inner diameter of between 1.9 mm and 2 mm.
• Obviously, zero friction is not possible, and materials such as PTFE are used to minimise it.
• Thermal cutting is not possible either and a behaviour which is as close to the ideal as possible is sought by using materials to provide the greatest possible insulation.

Hot-end families

Broadly speaking, there are three main hot-end families.

• Traditional hot-ends, comprising a series of parts and a PTFE tube (or materials with similar properties) inside.
• 100% metal hot-ends comprising a series of parts, also known as all-metal hot-ends, with no PTFE.
• Single body hot-ends, also known as UniBody hot-ends.

The two last types could potentially be combined, i.e. there could be an all-metal unibody hot-end, although this type of device is not currently available on the market (to the best of the author’s knowledge).

Traditional hot-ends

Traditional hot-ends have two main features.

Multiple parts

The advantages of multiple parts are the following:

• Modularity, as parts can be exchanged when breakages happen, or parts can be adjusted to needs, for instance, with the modification of the output hole: 0.4 mm, 0.3 mm, etc., or even for its adjustment for filaments with different diameters, usually 3 mm or 1.75 mm.
• Using different parts means that different materials can be employed, achieving better temperature control, using materials that heat up quickly, and with high thermal inertia properties in the heating block and thermal insulation materials in the upper part, preventing the heat from spreading to the extruder.

Meanwhile, the greatest disadvantage is that material can filter between the joints of the various parts, with an accumulation of waste that could lead to blockage of the extruder. This is more likely to happen when printing is completed with PLA-based materials, as these are more fluid than ABS.

Internal PTFE tube

The goal of PTFE is to minimise friction between the filament and the inner surface of the hot-end, thus allowing extrusion to take place.

The greatest disadvantage of PTFE is that it starts to deform and wear at temperatures above 240ºC, and this means that no printing with materials requiring higher extrusion temperatures can be done. Moreover, it experiences greater fatigue than metal and an issue is that extended use at high temperatures causes wear and tear.

The most popular examples of traditional hot-ends are j-head and budaschnozzle. Both of these types combine different materials to achieve thermal cut-off, but cannot print at temperatures above 240ºC, and they experience wear and tear of the PTFE tube and can suffer leaks of materials through joints.

Budaschnozzle cross-section

All-metal hot-ends

All-metal hot-ends are solely made out of metal. The major advantage is that very high extrusion temperatures can be reached, and printing can be done with materials like nylon or PTFE. However, although parts with low thermal conductivity are used to achieve thermal cut-off, a 100% metal extruder shall always have greater thermal conductivity than a traditional one, and therefore active cooling fans need to be used together with heat sinks. Meanwhile, metal involves greater friction with the PLA. This is minimised with the application of treatments such as electro-polishing inside the hot-end, but the same results as PTFE are never attained.

The most popular example of an all-metal hot-end is the E3D, allowing the extrusion of all kinds of materials but as there is no PTFE tube, there are issues in dealing with high friction materials and flexible materials. This hot-end also comprises various parts and there can be leaks among them and also jams as a result.

Unibody hot-ends

These hot-ends are manufactured with a single part, the greatest advantage being that there are no losses at the joints (because there are no joints), making printing a lot more stable even at high temperatures (for instance, PLA extrusion can take place at 220ºC with no leakage risk). Moreover, as heat sinks are in a single part with the rest of the hot-end, heat is dispelled better than with other solutions where heat sink fins are in a single separate part. The greatest disadvantage is that being a single part it is difficult to achieve thermal cut-off.

Bq’s hot-end is a UniBody one, and the inner tube is made out of PTFE to minimise friction. The greatest weakness is the wear and tear borne by the PTFE.

The video provided below explains the advantages of unibody hot-ends in respect of hot-ends with a series of parts

Unibody Hot-end HeatCore Maintenance

There are two significant maintenance tasks

1. Cleaning the inside of the hot-end, to prevent jams, to ensure that there are no materials and waste inside the hot-end when it is idle. This also extends the life of the PTFE tube.
2. Changing the PTFE tube, given that it will suffer wear and tear with extended use, and this shall lead to jams due to its deformation.

Cleaning the hot-end to prevent blockage

To clean the inside of the hot-end, acupuncture needles with a 0.4 mm diameter are used, and these needles are supplied with Witbox and also with Prusa i3 Hephestos. You can also buy needles here.

Watch this video to find out how to do it

Changing the PTFE inner tube

We are going to explain how to change the PTFE tube of the HeatCore Unibody extruder. This must be done when no extrusion is taking place or when extrusion with little density is occurring. Should you have any queries, please get in touch with our technical support department using the email address: soporte3d@bq.com, as the operation may be complex.

The following tools are required for the change:

The PTFE tube is situated in the internal part of the hot-end and, therefore, before starting the change we need to disassemble the carriage from Axis X of the extruder. Remember to heat it and unload the filament beforehand.

Step 1 Using an Allen key measuring 2.5 mm, loosen the two screws fastening the fan and the heat sink to the block (body) of the extruder.
Step 2 Use the 1.5 mm Allen key to loosen the grub screws fastening the hot-end to the block. Please remember to insert the key skilfully before loosening, as this a small grub screw that can suffer damage when not handled with care!
Step 3 Now take off the screw plug on top of the hot-end. The main purpose of this screw is avoiding movements of the tube inside the hot-end. Hold the hot-end with one hand and use the other hand to hold the pliers. Using a little force, unscrew the grub screw.
Step 4 Please consider that the state of the PTFE tube may have caused the entrapment of some filament remains in the hot-end. Using a clamp, hold the hot-end so that it is isolated. Please be extremely careful when doing this as you will need to heat the hot-end to a temperature of 200 to 220ºC. Use the tool to hold it and make sure it is firmly in place to avoid any accidents.
	Now connect the hot-end to the printer. The following cables will be connected: Heating cartridge: heats the hot-end. Thermistor: this sensor measures the temperature of the hot-end. Switch on the printer and using the LCD menu select the option called “Preheat” and wait until the hot-end reaches the target temperature provided in the LCD. After this temperature is reached, use the pliers to carefully pull out the filament trapped inside. This may be tricky, so please be patient.
Step 5 There is a white tube inside the hot-end and this tube is called PTFE tube. To remove the PTFE tube, a screwdriver and a screw used for wood will be used. The screw has to be placed inside the tube’s hole. It must be placed inside until both items are joined together and for this operation the screw used shall be 16 mm long, and it will be inserted almost up to the head.
Now use the pliers to pull from the screw and it will come out together with the tube. Please be careful, remember that the hot-end is hot! Once you have removed this part, switch off the printer and disconnect the hot-end (heating cartridge and thermistor) and let it cool down.
Step 6 Now insert the new PTFE tube in the hot-end. This tube shall have the following measurements: Ø on the outside 4 mm, Ø on the inside 2 mm, and a length of 19.4 ±0.2 mm. You can use the cone end of the lid to push it to the end. After inserting, screw the lid on again. Make sure the lid is tightly fastened on the hot-end and use some pliers for the few last turns when you are screwing the lid on.
Step 7 Now you have changed the hot-end PTFE tube, you only need to assemble the extruder for it to be ready and working.

Please watch the following video to change the PTFE tube of your HeatCore Unibody Extruder:

• Fotos_cambio_PTFE

  Photos of the process of changing the PTFE tube | CC-BY-SA