Briefcase sized, portable plastic grinder/filament extruder/spooler

A small shredder, hand-driven by a ratchet...

The "Filastruder" uses a soda bottle for a hopper...

These are part of why I think it CAN be done into a small briefcase-size unit, where most of the unit is actually a fold-out hopper that can double as reel storage.

The shredder might need a motor with quite a bit of torque though depending on the intended duty cycle. Just thinking of typical compact paper shredders here which can overheat after only a few minutes of continuous shredding of a few sheets at a time. Can gear it down but I suspect that shredder blades will have an optimum speed to chip the plastic rather than to chew it.

High torque drill, maybe?

Would perhaps first need to work out how much material needs to be shred in order to have enough raw plastic to extrude a usable amount of filament in one go before choosing an appropriate sized motor.

I'm assuming that if touring with this briefcase then time will be limited, so probably looking at stockpiling the bottles beforehand then straight into near-continuous shredding upon arrival, and extrusion into reels of filament, whilst consultations about prosthetics and 3D design take place. Then as soon as the first reel is ready 3d-printing can start.

I've just weighed an empty 2pint milk carton here and it weighs around 25grams. Googling and you appear to get just over 100m of 3mm diameter filament per kilogram of plastic.

Filament volume and length – ToyBuilder Labs

So that's around 2.5m of filament per milk carton, or around 40 such cartons requiring shredding for each 100m spool.

A high torque cordless drill motor is compact however it's not really designed to run continuously for any length of time. Entry level bench pillar drills tend to have 1/3HP or 1/2HP electric motors but they are large and heavy.

My crosscut office shredder here is rated at around 1/5HP and definitely would not be up to the job.

Looking at the Precious Plastic shredder build and they are suggesting a motor rating of around 2.7HP running at  @ 70RPM. Sounds a lot however perhaps required for 'just works' type operation.

Would perhaps first need to work out how much material needs to be shred in order to have enough raw plastic to extrude a usable amount of filament in one go before choosing an appropriate sized motor.

I'm assuming that if touring with this briefcase then time will be limited, so probably looking at stockpiling the bottles beforehand then straight into near-continuous shredding upon arrival, and extrusion into reels of filament, whilst consultations about prosthetics and 3D design take place. Then as soon as the first reel is ready 3d-printing can start.

I've just weighed an empty 2pint milk carton here and it weighs around 25grams. Googling and you appear to get just over 100m of 3mm diameter filament per kilogram of plastic.

Filament volume and length – ToyBuilder Labs

So that's around 2.5m of filament per milk carton, or around 40 such cartons requiring shredding for each 100m spool.

A high torque cordless drill motor is compact however it's not really designed to run continuously for any length of time. Entry level bench pillar drills tend to have 1/3HP or 1/2HP electric motors but they are large and heavy.

My crosscut office shredder here is rated at around 1/5HP and definitely would not be up to the job.

Looking at the Precious Plastic shredder build and they are suggesting a motor rating of around 2.7HP running at  @ 70RPM. Sounds a lot however perhaps required for 'just works' type operation.

Drills with the impact and hammer-drill settings are intended for heavier, longer operation, since that is for masonry and concrete.

The collection and prep phase might further be defined, as well.  Suppose that the collection and prep is only one type of bottle, since we've already specified one type of plastic, to reduce the need to disassemble and clean.  Clean and cut into relatively flat pieces, and run them through an office shredder, followed by low-heat, to insure dryness.  Caps, tops, bottoms and handles could be set aside, to be recycled using a larger grinder.  For purposes of airline mobility, restricting the plastic makes sense.  When using an automobile for transportation, it would be easier to have a larger grinder.

Once the smaller pieces are pre-shredded (think typical strip-shredder) for the final-grinder/extruder, the final grinder isn't having to do all the work.  Its' purpose is to make the final pieces small enough to feed into the melt chamber and extruder, not ground-down from chunks.

When things gear-up, it might be practical to have several interchangeable extruder heads, for different plastics, rather than trying to clean one out, for use with different plastics, so designing a setup with multiple temperature presets makes sense, either way.

Realistically, I'm trying to help a teacher do more.  Most of their printing is done in the classroom.  However, a fully portable mini-factory could be considered as a more prudent setup, for those with limited space.  If the extruder and the printer both close down to briefcase size, then it can be more practical for home use, mission trips, demonstrations, etc.

A demolition hammer drill motor/gearbox might do the trick - they are rated at around 2HP but are still fairly compact.

I'm not 100% convinced about the cutting of the bottles - you are likely to end up with injuries. Crushing them flat however may help feed them into the shredder cutter. However a shredder like this appears to make quick work of whole bottles and will probably feed ok if there is enough weight of material in the hopper

https://www.youtube.com/watch?v=j6Ghwd29W-o

Alternatively some sort of a feed tube where the next bottle inserted effectively pushes the previous one into the cutter

In a later design they added a mesh under the shredder which appears to grate the shredded material into smaller pieces.

https://www.youtube.com/watch?v=VFIPXgrk7u0#t=10m10s

Not sure how small you can make a cutter that still will bite into a bottle.

This video shows pretty coarse plastic pieces going into the extruder unit

https://www.youtube.com/watch?v=p4NoY33-Tfo#t=15m48s

so it looks like grinding may not be absolutely necessary.