Print Cooling Fan modification to 60mm (Noctua Fan)

This is a fan duct / shroud that allows you to mount a 60mm square fan to a MK2.5s or MK3s extruder assembly. 

The fan duct / shroud was inspired by https://www.thingiverse.com/thing:3019115. Chroja unfortunately had it designed for a MK2 extruder cover assembly. The mk2.5s and mk3s has a revised extruder cover assembly that provides a 2nd screw mounting location for better strength and stability of the original 5015 print cooling fan. 

For owners of MK2.5s machines, you will eventually experience that the 12V print cooling fan is no longer available from Prusa. I even checked digikey/mouser and directly with Sunon who made the original fan that the 12V version is end of life and an obsolete part number. 

The alternatives are poor quality 5015 fans off of Amazon/Ailbaba and ebay that fail quickly.

In my opinion Noctua makes some of the finest fans for which I installed a NF-A6x25 FLX to my mk2.5s. Note that MK3/MK3s owners will need the 5V equivalent of this fan (user to verify correct part numebr).

The part was design with best possible flow dynamics (no sharp edge where possible, smooth radius, and no sharp corners. The outlet matches the same dimensions as the 5015 Prusa fan (19.6mm x 15.0mm). 

Note: surface finish matters, so enable the cooling fan during print to get the best possible surface. Smooth surfaces = laminar flow = better cooling performance 

Print with:

-No support

-w/ cooling fan enabled

-5 line vertical perimeters to avoid having to use infill

BOM:

4x M3 washers

4x M3x30mm SHCS

2x M3x8mm SHCS

2 zip ties

petg filament

Install (MK2.5s, MK3 and MK3+ are simlar… wiring is different as it's 5V):

1. Remove old 5015 fan
2. Splice in the female connectors from one of the unused noctua fan cables in the Noctua kit (I chose to strip, wrap, flux, solder, clean, shrink tube my splice).
   1. Ignore the yellow signal wire. It's not used for mk2.5s
3. Install qty 2 of M3x8mm SHCS to extruder cover (tight, but not crushing tight)
4. Check fan flow direction
5. Fan wires exit the fan's housing at the 11 oclock position
6. Install qty4 M3x30mm + qty 4 M3 washers while also making sure to:
   1. route fan wires under the bridge of the Fan duct
   2. route fan wire between the SHCS and fan frame at the top right corner
7. zip tie the connector to the bottom right fan duct support arm
8. Check for obstructions

N.B. Print cooling settings going forward:

• Fan must always be enabled in Prusa Slicer
  • Why? Because the fan shroud/duct has a significant amount of volume. The default Prusa Slicer code assumes a normal blower motor, where when it's commanded to turn on, it does not need to fill a fan duct with air, and compress the air, and for the air to then exit the blower fan to the part being printed.  
    • If you use the default fan settings, the cooling air in this new configuration (60mm fan + fan shroud/duct) is effectively always discharging late compared to when the tip needs it, or no cooling is done at all…
  • Set fan low speed to 85% to 90% (so it is always blowing air) to maintain the Fan duct/shroud to be filled with air. The amount of air that is cooling part is negligible since a square fan has very low pressure output when not at 100% duty cycle. 
    • I've noticed that Fan speed < 70% and the Noctua fan does not spin 100% of the time, it spins up and down. I think that translates to Prusa menu>Tune>fan speed>177 in bits…
    • I've had best experience with fan % around 88%
    • Please comment with your experiences.