I have a nema 17 motor and MK8 extruder. Unfortunately my nema 17's power is not enough to turn and push the filament. I desided to make printed extruder with herringbone gears by using the motor and mk8 extruder's gear.
Printable Parts: Body Tensioner 9 Teeth Motor Gear 45 Teeth Extruder Gear
Needs: MK8 Extruder Gear 3 Piece 5x5x16 Ball Bearing (625rs, 625zz or any tipe of 5x5x16 bearing) M3 Bolts For Nema17 M5x55 Bolt M5x40 Bolt M5 Nuts M5 Washers 5mm Diameter 10mm Pin 15mmX6-7 mm Diameter Tension Spring TFE Tube And Connector