Extruder
The extruder is the core of the printer. It is where the plastic gets drawn in, melted, and pushed out. It is essentially a fancy hot glue gun. It is small, but it is where most of the printer’s technology is located. The extruder consists of two parts; the hot end and the cold end. The cold end has a motor that draws the filament in and pushes it through. The hot end is where the filament gets melted and squirted out.
Direct Drive vs Bowden Extruders
On direct drive printers, the hot end and cold end are connected together, one on top of the other. The filament goes straight down through the cold end and into the hot end.
With a Bowden setup, the hot end and cold end are separated. The cold end will be stationary and bolted somewhere onto the printer’s frame. The filament is pushed through a long tube (called a Bowden tube) to the hot end. This means that the printer has less weight to move around.
Hobbed Gear
This gear bites the filament and pushes it down through the hot end
Hobbed Gear
Idler Gear
The idler is a spring loaded wheel that pushes the filament up against the hobbed gear. Most printers have a way to adjust the tension on the idler, so that it neither squeezes the filament too hard or too little.
Idler
Hot end - All Metal vs PEEK/PTFE
By not using any plastic insulators in their construction, all metal hot ends are able to reach much higher temperatures and print a wider range of materials. However, they require active cooling.
Hot end - Heat Sink / Hot End Fan
This ensures that heat does not travel up the plastic and melt it prematurely before it reaches the nozzle. This phenomenon is called heat creep and it causes jams, especially with PLA. This fan should be running whenever the hot end is warm.
Heat Sink
Heater Cartridge
The heater cartridge is pretty self explanatory. It heats the plastic. It is simply a high power resistor. Almost all modern printers use cartridge heaters, but many older printers used coils of nichrome wire (like the kind in a toaster). If you are replacing your heater cartidge, of even your entire hotend, make sure you know if your system is running 12v or 24v.
Heater
Thermistor/Thermocouple/RTD
These are all various types of sensors for determining the temperature of the hot end. They are essentially electronic thermometers. Thermistors are the most common type of sensor, but some printers will use thermocouples for extremely high temperature printing.
Thermistor
Nozzle
The nozzle is simply a piece with a small hole for the melted filament to come out of. Nozzles are interchangeable, and come in various sizes; 0.4 mm is normal, while you might use a smaller nozzle for finer detail or a larger nozzle to print faster. Nozzles can also sometimes get clogged. This is one of the most common issues with 3D printers. See this article for advice on unclogging your nozzle.
Nozzle
Layer cooling fan
This fan cools off the plastic immediately after it is deposited by the nozzle. It helps the object hold its shape. The slicer will turn this fan on and off under different circumstances, depending on what material you are printing. It is not to be confused with the heat sink fan, which cools the hot end itself and not the printed object.
Layer Cooling Fan