The Problem with Hob Gear Extruders
The hobbed gear system provides only a limited amount of contact surface area between the printing filament and the mechanism controlling the filament – This limits the amount of force that can be exerted onto your filament.
The hobbed gear is constructed from metallic material which slip easily on polymer and in particular flexible polymer – This limits the amount of force that can be exerted onto your filament.
While the hobbed gear offers some degree of grip however the aggressive nature of the small serrations can easily become clogged with filament debris – This limits the amount of force that can be exerted onto your filament.
If the hobbed gear is driven too fast the serrations will gouge out and damage the filament profile. This will not only limit the amount of force that can be exerted onto your filament but damaged filament will ultimately lead to under extrusion or complete print failures.
The fundamental design of the pinch type roller system also makes it difficult to completely contain the filament. The removal of any cavities along the ENTIRE filament path is essential when printing flex. The solution in the past has been to insert a PTFE tube close to the pinch rollers, a simple solution but really not very satisfactory.
One big problem lies in the fact that to produce force with flexible filament the pinch rollers need to squeeze the filament and as the force is localised the pressure distorts the cylindrical profile of the filament, as it leaves the rollers it is elliptical and you can not fit a oval profile into a round PTFE tube without creating excessive friction. To overcome this you need to either limit the amount of pressure exerted on the filament or you need to leave some space to allow the filament profile to resume the original cylindrical shape before entering the PTFE tubing and as we know – any cavity no matter how small along the filament feed path is bad news for flex.
The Flex Wheel – Designed for flex but prints everything the best.
International Patent application pending.