I don't do a ton of soldering, but I *hate* the fumes that are produced and am too cheap to buy a $100+ HEPA or activated charcoal soldering fume extractor. I decided I would try making my own for a little cheaper. Here's what I used:
1x Holmes-Type Air Filter (I bought a HEPA one at Target for about $20)
1x 12v Power Supply (Check your junk drawer, these are one of the most common type of "wall wart")
1x 2.1mm female power supply connector (to match above)
3x 80mm computer fans (I bought new ones for about $3 each, shop around or scavenge from old hardware)
1/2" plywood or other enclosure material
1x 5" x 10" screen (nylon, wire, or something similar will work)
1x SPST switch (pretty much any cheap switch will work to turn it on or off, or you can simply unplug the power supply)
1x 200 Ohm linear trim potentiometer (this is optional, and probably not needed)
1x activated charcoal filter sheet ($6 online, because I don't believe in such thing as "overkill")
I did this in one day without a lot a foresight, so I HIGHLY recommend reading through this whole Instructable before building anything. Read the final section on "What I'd do differently" if nothing else. :)
Step 1: Constructing the Enclosure
Building the enclosure is pretty straight forward, and can be accomplished a myriad of ways. I actually designed an acrylic enclosure to laser cut from Ponoko, but the cost was a bit prohibitive for me. I used some scrap plywood laying around and cut two 5 1/4" x 8" panels for the sides, and two 8" x 11" panels for the front and back. I also cut two 5 1/4" x 10 1/2" panels out of 1/4" plywood for the fan and filter shelves. Take one of the large panels and cut the air intake hole/area. Then I simply dado-ed the vertical pieces to hold the fan and filter shelves. The top dado is about 1/4" from the top and 1/4" wide to accommodate the fan shelf. The second dado should be about 2" lower, so that there is some room for the fans, mounting hardware, and electronics. I then drilled holes for the power supply connector and the on/off switch on one of the side panels. I choose the side so that I would have the ability to place the extractor on it's face and have a larger air intake area if needed. I rabbeted the front and back panels to keep measurements simple during assembly. Finally, I used 2 1/4" pieces of wood for the fan and filter shelves. Cut appropriate holes for each! Finally cut some blocks to hold the filter in place.
Step 2: Assemble the Enclosure
The next step is to start assembling everything. For this step, I first bolted the fans to the fan mount shelf, as it will be a little tight to access once it's glued together. I then glued the front, sides, and the two shelves together, replaced the back piece (with no glue), and clamped everything together for a few hours. Once the glue was dry, I drilled some pilot holes for screws to hold on the back panel. Then I removed the clamps and the back piece, and fit the filter retention blocks with the filter inside the enclosure. A little more glue and clamping (remove the filter before the glue dries so that it isn't accidentally glued into place) and the filter retention blocks are set. The front piece and the filter are not glued so that the filter can be easily replaced at a later date. At this point I did a quick test assembly and then stained the enclosure. After the enclosure is dry, attach the screen to the top of the enclosure to prevent anything from falling into or touching the fans when running. (This is missing from my photos, but you definitely want this for both safety and aesthetics.)
Step 3: Wire It Up!
Almost done now! All that is left is to wire up everything. Fortunately, there isn't much to this step. Cut the connectors off the fans and wire the fans in parallel, not in series. This means soldering all the red wires together, the back wires together, and the yellow wires (if your fans have them) together. Black and Yellow gets soldered to the ground terminal of your PS connector. Red should be connected to the switch and then trim pot if present, and then to the positive terminal of the PS connector. Test to make sure everything is working before any permanent soldering or hot gluing! Once everything is verified as working, you can permanently mount the switch, PS connector, and trim pot, and solder everything. I glued the trim pot to the corner (remember to recess this a bit if you dadoed and rabbeted the front and rear panels like I did). For my build, the fans really needed to be on full power anyways, so the trim pot could have been easily omitted. Doing this simplifies the wiring some and reduces the cost by about a buck. :) Finally, I placed the activated charcoal filter between the fans and the HEPA filter. If I were to do this again, I'd add one more shelf and put it about 1/4" above the HEPA filter, so that the charcoal filter is sandwiched between the two shelves. Finally, screw the back on with some small screws and marvel at your creation! Oh, plug in the power supply and turn it on too. :)
Step 4: Final Thoughts (and What I'd Do Better Next Time!)
There's a couple of things I would do differently if I were to attempt this a second time. First off, I wasn't very exact when I created the hole for the fans, which could affect air flow. Keeping the all the parts airtight will definitely increase the efficiency of the extractor. Second, after completing the build, I realized that the three fans worked best when run full speed, so there is really no need for the potentiometer. Finally, I would add one more shelve to accommodate holding the charcoal filter securely between the new shelf and the filter shelf. Of course, many may find that the extra filter is probably not needed, but I feel it's a nice addition to the build, and one doesn't actually have to place a filter in the space to get an operational extractor. I also placed a screen (nylon netting) on top of the fans on the outside to prevent anything from falling into the fan area.