Hotend: the hot part of the print head

What a hotend consists of

A hotend is the assembly that guides filament from the top down into the hot zone. The main parts are a heater cartridge or ceramic heater, a temperature sensor (a thermistor), a metal block in which the plastic is melted, and the nozzle at the end.

Above the hot zone is a heatsink with a fan. It keeps the upper part of the filament solid, so the plastic does not melt too early and jam. Between the hot and cold zones is a thin metal tube, the heat break, which separates the heat.

Temperatures and materials

Typical nozzle temperature is around 200 to 230 °C for PLA and around 230 to 250 °C for PETG. The exact values are set by the filament maker and the profile in the slicer. At a higher temperature the plastic is runnier and bonds better between layers, but it oozes more and makes strings (stringing).

A hotend that goes to higher temperatures can also handle engineering plastics, but we only print PLA and PETG, which sit in the normal range.

What can go wrong

• Heat creep. When heat climbs too high, the filament softens before the hot zone and jams (heat creep).
• Clogging. Dirt or burnt plastic blocks the path (clogged nozzle). The part then does not get enough material.
• Plastic leaks. If it is tightened badly, molten plastic escapes around the nozzle. That is why a hotend is tightened hot after a change.

Speed, flow and your order

Print quality rests on a stable temperature and a smooth supply of plastic. You do not set anything on your order, but uneven layers or holes in the walls are often a sign of a problem in the hotend. That is why we photograph every batch before dispatch.

The hotend not only melts plastic, it also decides how fast you can print. The plastic has to have time to melt as it passes through the hot zone, so there is a maximum volume the hotend can handle per second (flow rate). A bigger block and a stronger heater raise that limit.

If the speed in the slicer is set higher than the hotend can keep up with, the plastic does not melt completely, under-extrusion threatens and the part is weaker. So our print speed is not just a number on the machine but a compromise between time, strength and looks. The same principle is behind the fact that printing goes faster with thicker layers.