Prusa i3 MK2 Clone Extruder for 18 mm sensors and MK8 Hobbed Pulley

Regenerated the18mm version, as in the18mm version the sensor holder must be moved 8 mm to make room for the fan.

I Use:
* the Prusa MK3 Nozzle fan for the MK2(S): https://www.thingiverse.com/thing:2717991
* the extruder-cover-cut-moved-MK3: https://www.thingiverse.com/thing:2717991 for a clone extruder with a 1mm moved extruder.
*Anet A8 x-carriage for E3D Prusa MK2s i3 extruder: https://www.thingiverse.com/thing:2494988

The 18mm sensor is approximately 39mm right and 3mm back from the