Why are filament extruders so slow?

Is it because they're cheap? Do you have to 10X the budget to extrude quickly? What about filament extrusion makes it so slow when regular printing extruders can go so much faster?

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The tolerance between screw and tube is not nearly good enough, the surface finish of the tube is often very wrong, the surface finish and geometry of the screw are really bad, the motor spins way too slowly and does not have enough torque, and the nozzle design is bad. The extruder is also often too short.

Basically what you want is better motor and NC machined tube, nozzle and screw. A good motor and controller can cost 1000€, and machining the other parts can cost 2000€. So yeah, basically at least 10x more money than a hobby extruder. Commercial machines cost something like 50k-100k ->

Edited 2 time(s). Last edit at 06/05/2014 04:22PM by jkoljo.

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MrDoctorDIV
What about filament extrusion makes it so slow when regular printing extruders can go so much faster?

"Much faster"? Do you have a printer that can churn through 1kg in under 8 hours?

Motor power is roughly equal to the cube of extrusion speed. That means quadrupling extrusion speed requires a motor 64 times more powerful. That gets expensive quickly.

Edited 1 time(s). Last edit at 06/06/2014 06:22PM by greenman100.

Theres a big difference in volume between a thread 0.3mm x 0.42mm versus a thread 1.75mm x 1.75mm (using recent common settings).

Now, if you are asking what it takes to make them go faster:

1. Heatzone: You need a longer heatzone. The pellets need enough surface area contact to melt in time before reaching the die.

2. Torque: In order either increase the speed of your screw, or increase the diameter you need greater torque than the tiny gear motors currently used. The motors used are reaching the limits of torque available compared to just switching over to industrial motors running on AC with traditional gear boxes.

3. Design: In order to reliably extrude to the tolerances that should be reached for filament, screw design is a must. Lyman cheated with using a $15 auger bit. Its a simple conveyor concept which pretty much limited the speed to reliably maintain quality tolerances. If you want to extruded to your specified speed, you design the extrusion screw with a feed zone, a melt zone, and a metering zone, specifically matched to the screw L/D ratio and the material properties fo what you are extruding. You also need to design your die accordingly afterwards. And for better quality control, post-processing techniques (like water bathing and pressing) help maintain the tolerance.

But dont take my word for it:

Basic Screw Geometry

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