## Step 3: Calculations

Enter the mighty trigonometry functions.

First we need to figure out the displacement of the CPU fan when looking at it from above. In my example, the fan was 1-1/4" lower and 3/8" to the right of the vent hole. Plug this into the Pythagorean formula to get a displacement of 1.305" (about 1-5/16").

The number we just found is crucial for the next step. We need to figure out how long to cut the PVC and at what angle. We know the CPU fan sits 3-1/2" into the case, but we can subtract 1/4" because of the plywood piece that mounts the PVC. That leaves us with 3-1/4" deep and skewed 1-5/16" laterally. The Pythagorean formula gives us a total length of 3-1/2" for the PVC.

The angle can be figured out using tangent. With the opposite and adjacent sides known, one can easily figure out the angle theta in the third diagram. However, the saw must be set to cut at an angle of 22 degrees, not the 68 we found (90 - 68 = 22).
<p>does it have to be slanted? why not straight<br></p>
I made this for my CPU before i read this. Te effect was awesome. The cpu was overclocked and it still maintaining tempriture below 40 C. About the dust ... it always intakes dust so frequently cleaning is important even without this .
wonderfull instructable i liked this fan duct technology i must admitt that you are the only one gave me most advantages to my laptop since i recently joined you
does it intake alot of dust
yea
my fan is JUST out of line with my CPU.. >:(
I remember somewhere i was that they put a tube over the processor and a supercooled liquid(not sure what it was though) and overclocked it to 5000mhz !
Youtube, liquid nitrogen. Very cold. it was Over 5ghz
yeah i also saw it on something on tv
ive benn needing this beacause my server heats up
at Xoxide.com
kool, i bought three light up fans for \$3.99 each at \$2.55 shipping, for all of them
A chrome version and a clear version would be great for gamers aswell, also I noticed my miter saw has a dent in it running along (like a little guide or something) perfect for keeping round stuff straight 'n true. I didn't make this for the computer but the ideas came in handy for another item. hence the metal one, I needed a similar item for the forklift air intake because all of were nicking our arms on the fan blades while spraying ether in to the intake and cranking the starter. Extend the intake with this. Also thanks to this there's no longer a stupid rubber intake thankyou very much for reminding me of my miter saw and pipes also the trigonometry was there already...
could you get some of those pre-shaped galvanized air conditioning and vent shapes (made out of thin metal) from lowe's/home depot and do this too? i think one of those would cost about the same and do the same thing
Sure. I just find working with those more annoying and troublesome. Metal ducting is a pain ;-)
I've been needing something like this...Thanks!
Great Instructable! I would have liked to see more pictures showing detail of how the duct fit inside and comparative results from before and after the installation.
I'll probably take some pictures next time I open the case. As it is it's just a pain to go under and unplug everything and open it all up, but I'll keep that in mind. There wasn't really any way to compare the before and after because I was already using a duct before I made this. I know that I got better cooling when I installed the original duct (and my CPU fan had to work less, gotta love AMD's Cool n' Quiet!). All I know is that this is much less hassle than the duct I had before and that's a good result for me :-)