A bottle cutter that uses 608ZZ skateboard bearings (8x22x7mm), and US pennies or 5/16 washers to adjust the cut width.

Parts

2, 608 bearings (8x22x7mm) (Grind at least one side flat to use as a shearing surface. I used an angle grinder and then a Dremel with a sanding head to smooth it out. If the surface is rough it is Much harder to cut the plastic.)

2, 5/16 or 8mm bolts and nuts ( Fully threaded bolts and 8mm bolts may need shims for the bearings to overlap properly. There is a remix that moves the bolt holes closer together if the holes don't work with your bolts.)

Several US pennies or 5/16 washers. Any metal disk with a diameter less than 19.2mm will work.

When making PET filament I prefer strips around 8.5 to 9mm wide. The wider the strip the rounder and more solid your filament will be, but it will also become thicker and harder to pull through the nozzle. I keep my nozzle at around 215 to 220 C when making filament. My filament comes out around 1.85 to 1.92mm in diameter. On a Prusa mk3 and an E3D rapid change nozzle the filament needs to be less than 2mm or it will jam. Filament that is too thin will also jam because the extruder can't grip it, but it's easy to remove.

Dry your PET filament after making it and before you print with it.

I Print PET on a Prusa mk3s with an E3D revo .6 or .8 nozzle

275 to 280 C Extruder (PET melts at ~260 C)

80 to 85 C Textured bed.

1.1 to 1.4 extrusion multiplier. (This is dependent on your filament diameter and how wide you cut the bottle strips.)

Update:

I rebuilt my PET filament maker nozzle out of a steel bolt and now my filament comes out at 1.75-1.8mm and is much easier to pull. The key was drilling the nozzle slightly undersized and then evenly polishing the inside of the hole using some metal polish on cotton or hemp string. This makes it really easy to fine tune the hole size. The hardness of the steel actually helps by wearing away slowly.

I now cut strips to around 9mm and print at 1.15 extrusion modifier.

Edit: added .stp file of model.