The most important part of the 3D printer. The extruder system is what feeds and heats the filament to the heatbed. The extruder system outlined in this post must suit the ultimaker style cartesian motion platform researched in the previous research post on motion systems. Therefore it has certain geometric constraining limits. Although since the motion platform has not been designed yet this will be a general research into what will the most effective extruder system considering the criteria set out by the brief.
The Standard Extruder Systems
Here are two of the standard extruder systems:
- Direct Drive
- Bowden Drive
Here is a diagram of the concept of a direct drive:
A direct drive system uses a filament drive gear system that is located very close to the top of the hotend. The drive gear is powered by a standard stepper or geared stepper. The close proximity between the drive gear and hotend makes feeding of filament a lot more efficient. Downside is that the stepper motor is part of extruder system which greatly increases the mass and lowers the possible acceleration and velocity rates. This system is generally regarded as the most reliable of the two standard extruder systems.
- More efficient feeding of filament into the hotend
- Less buckling of the filament due to close proximity of extruder to the hotend
- Overall just more reliable than other systems
- Higher mass due to the stepper motor
Here is a diagram of the concept of a bowden drive:
Similar to the direct drive system except that the filament is driven through a long PTFE tube which allows the stepper motor to not be part of the moving gantry system. This lowers the mass of the system. The system becomes less efficient because of greater distance the filament has to travel. Much higher retraction settings are needed because of the lag involved. Generally the bowden system can be less reliable than the direct drive and is harder to fine tune due to hysteresis.
- Lower gantry mass equates to higher possible acceleration and velocity
- Stepper assembly isn’t on the moving gantry which lowers the complexity
- Hysteresis of the filament makes it harder to fine tune and can effect reliability
Extruder System Selection
This was a very hard decision as the advantages and disadvantages of both systems fare evenly between them. But looking at the criteria needed for this printer. One criteria is that reliability is a key part of this printer and a direct drive is more likely to be more reliable.