This is a simple fume scrubber to help get rid of ABS fumes. It's intended to go inside of a heated build environment and keep the interior fume levels down without wasting heat by blowing them out.
The fan_mount_v2.scad file from http://www.thingiverse.com/thing:18273 is used. Either version of the scrubber just uses bulk activated charcoal (such as this: http://www.amazon.com/Acurel-LLC-Economy-Activated-Pellets/dp/B000YIWT0M/ref=sr_1_2?ie=UTF8&qid=1344565074&sr=8-2&keywords=activated+charcoal ) and can be attached with self-adhesive velcro. The STL files are for 40mm fans.
Version 3 (Round):
This one requires no filter material, you just pour some charcoal in the top. It works much better than v2, but is harder to print; slic3r wants to print the filter grid as a series of squares rather than as a grid. To counteract this, I offset the x and y lines in the z direction so that you get the first layer as a support and it seems to work for me. If you have a nozzle fan (I don't yet) I think this would work wonderfully.
I will probably be experimenting with different screen designs to see what prints the best. I'm fairly sure the best thing will be to have non-intersecting criss-crossing bars. That way slic3r should have it draw the x lines on one layer and the y lines on the next, then repeating.
Version 2 (Rectangular):
To use this you put a small piece of filter material between the grate and the fan and then fill the top with bulk activated charcoal and then put a small piece of filter in the top to plug the hole and mount. If your fan doesn't have a built-in guard (an X across it is enough, just not open) you'll probably want an external one between it and the filter to keep the filter out of it.
Version 1 (N/A):
This was abandoned and never uploaded. It would have been similar to V3.