Hello fellow tinkerers, the fan I made here was for a specific purpose (my home theater receiver creates a lot of heat that gets trapped in the cabinet that it's in, so I decided to build a fan system to vent the heat out the back), but this type of fan can be used for many applications. Since I had the metal grille, switch, and case fan laying around my house, I only spent one dollar on the power adapter at Goodwill.
What you will need:
-Drill and drillbits
-Dremel tool with cuttoff disk
-12 volt DC adapter
-Computer case fan
Step 1: Prep the fan and power adapter
I got my fan out of an old, useless desktop computer, but I'm assuming most people would simply buy a new fan (an 80mm fan like what I used should cost no more than 5 bucks). The fan probably has a plug end to it, so you're going to want to cut that off, leaving as much wire attached to the fan as possible. Strip the wire ends 1/4 of an inch.
Now take your 12 volt adapter and do the same thing, cutting off the small end. You want the plug and as much wire as you can possibly get. Just like the fan wires, strip the ends approximately 1/4 of an inch.