Extruding thin wires of consistent diameter is not easy: try manually extruding a sausage from your printer, by slowly turning the wheel. Through a 0.4mm nozzle, I can get sausages ranging from 0.05mm up to 1.0mm, by varying temperature and pressure alone.
The extruded plastic contracts length-wise after coming out of the nozzle, while still molten, as the molecules tend to go back to their usual curled-up shape (instead of being too stretched-out). This makes the diameter very unpredictable, and requires a very constant temperature, pressure, speed, cooling; and constant monitoring and adjusting.
If the filament diameter is only 10% off, then the area is 20% off, thus causing over- or underextrusion in your printer (if it still can pass through the bowden tube and nozzle).
So I don't think you will get very far with home-equipment, although it might be good enough for a doodle-pen?
Maybe you can find second-hand *professional* equipment from bankrupt companies, or from stopped production lines? Or from companies that upgraded to new machinery? If you can get these cheap, it might work well.
But even then the setup for each run may consume and waste as much material as a full spool. When I was a kid, in our neighbourhood we had a plastic company that produced straws for lollipops. At that time safety rules were a bit more relaxed, so we were occasionally allowed to walk around between the machinery, as long as we didn't touch anything. Each startup of the plastic extruder produced a huge bag of waste, before the flow was constant and smooth enough, even for lollipop straws.
It is not just the extruder: you also need the grinder, feeder, heater, dryer in front of the extruder; and behind the machine the long cooling trajectory with transport band, and the spool-winding machinery.
So you should rather do this as a learning exercise, and for the joy of creating new stuff, but not for economy.
A good filament recycler that yields good filament to use for under $300 would be the best thing since sliced bread, sorry sliced bread
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