There are 3 main types of extruders for Filament Fusion Printing (FFF): Direct Drive, Bowden and Remote Motor.
They operate on the same principles, and all three have their own advantages and disadvantages.
Direct-drive extruder motors are located just above the hot zone with generally little distance between the drive and this hot zone.
Direct-drive extruders reduce the required distance between the hot and cold zone of the extruder. This makes retraction easier. Retraction is the process by which the extruder pulls the filament backwards to move it away from the nozzle and reduce the pressure in the nozzle so that the filament does not ooze while the hot end moves in the vacuum. Direct-drive extruders do not need to shrink much, usually between 0.8 and 1.8mm.
Direct drive extruders also control the amount of material deposited very well, as there is little distance between the drive and the hot zone and therefore little bending or compression of the filament.
One of the disadvantages of having the extruder so close to the hot zone is that the motor weight is moved with the carriage, which can cause problems when printing at high speed. Additional weight means that your extruder can cause undulations on the part due to twisting of the mechanical elements during changes of direction.
Another disadvantage of the direct drive is its low tolerance to over-extrusion problems, poor Z-setting of the printing bed, etc. For example, if the diameter of the filament is not constant or the quantity of material is incorrectly calibrated, and there is too much extruded material, the direct drive extruder can machine the filament and become inoperative, the extrusion is stopped and does not start again.
The last disadvantage is that it is more difficult to make a heated chamber in a direct extruder (without falling into existing patents), as standard stepper motors are not designed to operate at more than 60/65°C.
Bowden extruders have the extruder motor placed at a certain distance from the hot zone, the motor is generally fixed to the printer frame outside the printing zone.
This reduces the weight on the printing carriage and allows faster printing.
One of the disadvantages is that it requires the filament to travel long distances to reach the hot end. Retraction distances generally have to be much longer than their direct-drive counterparts to compensate. Bowden extruders require a shrinkage between 4.0 and 6.0mm.
The second disadvantage is that flexible materials are practically impossible to print on a Bowden extruder because they deform along the filament path, swell and no longer extrude…
An advantage of the Bowden is that the extruder motor can be placed outside the chamber, which makes it relatively easy to make a heated chamber printer.
A Remote Motor extruder usually has the filament drive mechanism placed just above the hot zone, which gives excellent retraction, without hindering the head’s movements by adding the mass of the motor to the carriage because the motor is fixed outside the chamber. The power is transmitted to the extrusion head by a semi-rigid shaft (a bit like the flexible shafts for a Dremel)
Remote Motor extruders generally require a shrinkage of 1.5 to 2.0mm and allow the printing of flexible materials under the same conditions as a Direct Drive extruder.
The drive motor being placed outside the printing chamber, the latter can be easily heated.
They tolerate over-extrusion or poorly calibrated bed problems very well (as well as Bowden extruders), because the motor transmission cable smoothes pressure peaks in the nozzle, without having the disadvantages of the distance between the drive zone and the hot zone of the BOWDEN.