Compact direct drive extruder

Two compact direct drive extruders for 1.75 mm filament.
One inspired by MK8 extruder, another one - by bulldog extruder.
Can be used with flexible filaments.

Materials used:
- 695zz bearing
- (optional) PC4-M6 fittings
- PTFE tube OD 3mm / ID 2mm
- Springs length 22mm / OD 7.5mm / ID 5.2mm
- Drive gear
- M5x10 and M3x6, M3x8 and M3x16 screws