Basic hotend maintenance

The hotend is one of the most important components of an FFF 3D printer and the one that undergoes the most wear and tear. It is essential to carry out proper maintenance and periodically check its condition.

There are multiple types of hotends, both standalone (e.g., E3D V6) and integrated in compact hotend assemblies (e.g., Hemera, LGX FF), however, they all have a series of common components.

Image 1: Hotend integrated in the LGX compact hotend. Source: bondtech.se

In any hotend, we can find the following components:

• Nozzle: This is the element through which the melted material is extruded.
• Heater cartridge: It consists of a resistor whose function is to heat the heating block.
• Temperature sensor: It can be of different types: thermistor, thermocouple, PT100,... Its function is to measure the temperature of the heating block.
• Heating block: This is the element responsible for transmitting the temperature to the nozzle and the hot zone of the heat break.
• Heat break: This is the thermal break element. Its function is to guide the filament to the nozzle, preventing it from melting prematurely. It consists of a hot and a cold zone, and its thermal performance is fundamental for the proper functioning of the hotend. There are two different types: all-metal and with a PTFE insert. The all-metal heat break withstands high temperatures but is prone to heat creep when its thermal performance is not optimal. The hotend with a PTFE insert prevents the filament from melting inside the heat break and minimizes friction inside it, however, it is not recommended for materials requiring temperatures above 265 ºC.
• Heat sink: This is the element responsible for cooling the heat break, keeping the hot and cold zones separate. It can be passive or active.

Image 2: Parts of a hotend. Source: cults3D.com

To ensure the proper functioning of the hotend, it is necessary to check both the condition of each of the elements and the assembly of all of them.

Nozzle

This is a consumable element and therefore has a limited service life. Nozzle wear will cause an increase in the output diameter and a reduction in its length. This will result in inconsistent extrusion that will deteriorate the finish of the parts.

There are several factors that accelerate the wear of a nozzle. The most common is the use of composite materials. The presence of fibers or particles in the filament produces high abrasion on the walls of the nozzle. Filaments of fiberglass or carbon, those loaded with ceramic or metallic particles, and phosphorescent filaments are especially abrasive.

On the other hand, the material from which the nozzle is made will also define its durability. The most common materials are:

• Brass: These have a very limited durability, even with non-abrasive filaments. It is advisable to replace them often to ensure the highest print quality.
• Brass or copper with nickel coating: The nickel coating provides greater surface hardness to the nozzle and therefore greater resistance to abrasion. Its durability is very high with non-abrasive filaments and moderate with abrasive filaments.
• Stainless steel: These nozzles are developed for medical and food contact applications, however, they have good durability with non-abrasive filaments. Although they have moderate durability with abrasive filaments, they are not the most recommended option.
• Hardened steel and similar: These have good durability when used with abrasive materials and very good with non-abrasive filaments. In general, the print quality is not as good as in the previous cases due to the roughness of the material and its adhesion with the molten plastic, however, some incorporate special coatings that solve this problem.
• With ruby tip: Ruby is one of the hardest materials and suffers the least wear, however, only the tip of the nozzle is made of this material, which is crimped in a brass nozzle. It has high durability with non-abrasive materials and its main advantage is that it does not lose quality throughout its service life. Over time, the brass part wears out until the ruby tip comes off. With highly abrasive materials, it is recommended to use hardened steel nozzles.

Image 3: Brass, nickel-coated copper, and hardened steel nozzles. Source: Brozzl.com

It is difficult to estimate how often a nozzle should be replaced, as it depends largely on the material used and the temperature, however, as a rough guide, the following values can be estimated:

• Brass nozzle:
• With non-abrasive materials: Replace every 200 hours of use.
• With abrasive materials: Not recommended.
• Nickel-coated brass nozzle:
• With non-abrasive materials: Replace every 1000 hours of use.
• With abrasive materials: Replace every 100 hours of use.
• Stainless steel:
• With non-abrasive materials: Replace every 1000 hours of use.
• With abrasive materials: 100 hours.
• Hardened steel:
• With non-abrasive materials: Not recommended.
• With abrasive materials: 400 hours.
• With ruby tip:
• With non-abrasive materials: when the ruby comes off.
• With abrasive materials: when the ruby comes off.

Heater Cartridge

The most common failure related to the heater cartridge is due to a connection problem. The wires entering the cartridge are usually protected by two temperature-resistant plastic sleeves. These sleeves tend to degrade with use, exposing the metal wire. As soon as the wear is evident, the heater cartridge should be replaced, as the loss of insulation from the wires can cause a short circuit, fire, or serious damage to the user.

Temperature Sensor

Like the heater cartridge, the most delicate point is the connection of the wires. Damage to the wire or its connection will cause erroneous and erratic temperature readings. If the wire breaks completely, the temperature value will remain fixed at its maximum value. It is advisable to check the condition of the connections frequently.

Image 4: Different formats of NT100 thermistor. Source: alibaba.com

Heater Block

Although it does not require any specific maintenance task, it is very important to keep it as clean as possible. Accumulated plastic residues can detach and adhere to the piece during printing, causing aesthetic defects or even printing failures. The use of silicone sleeves or plastic repellent coatings can help keep the block clean, especially when printing with materials such as PETG. In the case of using silicone sleeves, it is advisable to remove and clean them regularly, as well as replace them as soon as they begin to degrade. In the case of the non-stick coating, it is recommended to apply new coatings every 2 or 3 prints.

Image 5: E3D Silicone Sleeve. Source: e3d-online.com

Heatbreak

Completely metallic heatbreaks do not require special maintenance. If abrasive materials are printed regularly, it is recommended to disassemble the heatbreak every 500 hours of use to check the wear of the inner throat. As soon as signs of wear begin to be observed, the heatbreak should be replaced.

In the case of heatbreaks with a PTFE insert, the insert suffers directly from wear. It should be replaced every 500 hours of use with PLA, every 300 hours of use with ABS or PETG, and every 80 hours of use with abrasive filaments.

Heatsink

The heatbreak is usually directly attached to a cooling element. This can be passive (finned heatsink) or active (finned heatsink + fan). Its ability to dissipate heat from the cold zone of the heatbreak is crucial to prevent problems. Excessive heating of the cold zone can cause the filament to soften and compress, causing a jam. This phenomenon is known as heat creep and is common when printing PLA in a hotend with a metallic heatbreak.

To ensure optimal dissipation, it is necessary to apply thermal paste to the junction of the heatbreak with the heatsink. It is advisable to use thermal pastes that also have anti-adhesive properties such as boron nitride, to facilitate the disassembly of the heatsink in future revisions.

In the case of active heatsinks, the fan operation should be checked at the beginning of each print. Some printers control this fan thermostatically, so it may remain off until the hotend reaches 50 ºC or 100 ºC.

Assembly

Because each element of the hotend is made of a different material and their coefficients of thermal expansion are also different, it is common for the joint between them to loosen due to sudden temperature changes. It is very important to check every 2-3 weeks that all elements and screws of the hotend are correctly tightened.

If the nozzle has loosened, it should be tightened again when hot. It is very important that the heatbreak and nozzle are tightened and in contact with each other, as a small gap between them will produce a leakage of melted material that will damage the hotend.

Image 6: Plastic leakage caused by poor hotend tightening. Source: forum.prusaprinters.org

The optimal tightening torque should be consulted with the manufacturer for each hotend, as excessive torque will damage the heating block thread. As a reference, E3D recommends a torque of 3 n·m for its hotends, while slice engineering uses 1.5 n·m. In the absence of a manufacturer's reference value, a torque in the range of 1-2 n·m can be used

It is also important to check the screws that hold the heating cartridge and the temperature sensor.

System Mixing

Original spare parts should always be used, or at least those belonging to the same system. Although it may often seem that there is compatibility between components of different systems, since they have the same type of thread, the length and dimensions of each element are also very important. The different components of a hotend have been designed to work correctly together, and mixing components that do not belong to the same system can cause malfunction or even damage to the hotend.

Material Changes

When a filament is removed from the hotend, there are always residues left inside. When loading a new material with a lower printing temperature, it will drag the unmelted residues of the previous material causing a jam. That is why whenever a material change is made, the hotend must be cleaned using a cleaning filament. To do this, between 500 and 800 mm of cleaning filament will be extruded at a temperature 10 ºC higher than that of the last material used.

The Layer Fan

Although the layer fan is not a component of the hotend itself, it is usually located next to it. A mispositioned layer fan can direct air directly to the block causing it to cool down. This causes the hotend not to reach the set temperature or for the temperature to fluctuate greatly, which usually results in a temperature error in the printer. In these cases, it is advisable to try the same print with the layer fan deactivated to verify if it is a temperature sensor failure or the effect of a poor position of the layer fan.

Filament Entry

A point of entry for dirt inside the hotend is the filament entry zone. In Bowden systems, where the filament is guided by a PTFE tube to the hotend, the entry is protected and it is not common for dust to enter, however in printers with direct extruders, the filament entry may be exposed to the air facilitating the entry of dust into the hotend. In these cases, it is advisable to guide the filament from the spool to the extruder through a PTFE tube whenever possible. The entry of dust and dirt into the hotend is a common cause of jams.

Likewise, it is recommended to keep the filament spools clean and prevent dust from settling on them, so they should be avoided to be left on the printer support if it is not protected and stored inside closed bags or boxes.

Printers with Multiple Hotends

When you have a printer with multiple hotends, you must calibrate the relative position of these.

First, it must be checked that the distance from the hotends to the printing surface is the same. To do this, the main hotend will be fixed and the printing base will be leveled with respect to it. Then, the height of the other hotends with respect to the main one must be adjusted. The way to adjust the height varies from one printer to another, so the equipment manual or the manufacturer should be consulted if you do not know how to do it.

Once the height of the hotends has been adjusted, it is necessary to know the relative XY position of each one with respect to the main one. In general, each manufacturer provides a printing file that allows calibrating the XY offset of each hotend, although there are also many other options in well-known file repositories. In this case, the XY position of the hotends cannot be altered, so the offset values will be entered into the firmware to compensate for the position during printing.

The height of the hotends must be checked every 2 weeks, while the XY calibration will only be performed when deviations or overlaps are detected in the parts printed with each hotend.

Image 7: Dual extruder calibration pattern for Raise Pro2 printers. Source: Raise3D.com

The hotend is probably the printer system that requires the most maintenance, however, it is very important to keep it in good condition to ensure good print quality and minimize the risk of failures.

Note: This guide discusses concepts in a general way and without focusing on a specific brand or model, although they may be mentioned at some point. There may be significant differences in calibration or adjustment procedures between different brands and models, so it is recommended to consult the manufacturer's manual before reading this guide.