Upcycled print fan for upshort cooling

Have you ever wished for a more personal summer breeze…?

This cheeky but effective little project repurposes your leftover print fan from the MK4/MK3.9 to MK4S/MK3.9S upgrade and channels airflow right where it’s needed most.

Designed to strap to your leg, the discreet enclosure hides the fan while pulling in fresh air and delivering it straight to, er, key areas.  Whether you’re working in the garden, grilling, or just trying to survive the heat, it provides just enough comfort exactly where it really matters.
 

Bill of materials

1 x print fan from your Prusa MK4/3.9 > MK4S/MK3.9S upgrade (outer assembly parts removed).
1 x standard 50x50mm 3 AA cell holder
3 x AA cells
1 x 10x10mm 5v step up (boost) converter - 2108A or similar; ubiquitous on AliExpress
1 x 6mm toggle switch (13mm wide) - common dimensions for switches of this size
3 x M3 8-12mm button head bolts for the fan
2 x M3 8-20mm button head bolts for the case
3 x M3 hex nuts
Wires, solder, etc.
1 x 20-24mm strap (I used 24mm) wide enough for your leg with hook-and-loop or other fastening method
 

Assembly

Wire the battery (of AA cells) to the input and ground of the converter with the switch in-line (I I used the ground wire) and the fan to the ground and output of the converter.

If this is unclear to anyone, let me know and I will make a diagram.  I can also provide links to parts if desired - I didn't include them here as the links would expire quickly.

The fan screws to the base plate and the battery can either just rest in place (the shroud has a protrusion to hold it down) or you can use an adhesive.

The switch bolts in using the nuts that come with the switch.  Insert this before the battery for insertion clearance.

Insert the base into the shroud and bolt in place.