Gearbox for standard bowden extruder

Update 21.07.2019: After 5 month of using it I made some changes:
- screws position and necessary length to offer an easier way to mount;
- M5x45 Hex bolt instead of M5x45 rod obtaining a more rigid axis.
If the motor doesn't get hot PLA can be used for small gear.
No further development.

A simple gearbox to improve your standard extruder.
The gearbox can be equipped with 3:1 ratio gears from Drakon extruder - https://www.thingiverse.com/thing:2172854
or 2:1 ratio gears - h