Why a Gearless Extruder Works for 3 mm Filament

While it is accepted dogma that one should always gear down a stepper motor to push 3 mm filamnet through an extruder - we think otherwise.

We start with principle calculations of filament strength. We know that it is possible to push 3 mm filaments strongly into the melt zone of an extruder, to push through the operative non-Newtonian fluid physics - of partially molten plastic being very viscous and thus hard to move. Read more - [1].

The maximum push force that an extruder can exert on a filament, at the limit of zero bending of the filament - would be equivalent to its tensile strength - about 5000 psi. [2]

3 mm filament thus has a 0.01*5000 psi maximum pull allowed on it, where 0.01 square inches is the cross sectional area of a 3 mm filament. This takes for 50 lb - which sounds about right. Let's say that compressive strength equals compressive strength. So at max, we can push with 50 lb.

How much force does a 72 oz in stepper motor, like the one we use, give? For an MK7 Drive Gear like we use -