All images are clickable for larger versions.
Some case fans like the Nexus 120mm Real Silent case fan
have "closed" corners. Most case fans have two flanges with a hole on each corner. With the "closed" corner fans each hole is connected by a tube to the corresponding hole on the opposite flange. I don't know if you can still understand me, so maybe some pictures will make it more clear.
The orange fan has "closed" corners. The black fan has the more standard corners.
These tubes sit in the way if you want to use vibration dampening rubber fan mounts
. Also when mounting such fans on a Thermalright XP-120
, the tubes get in the way of the mounting clips. Well, if the tubes are unwanted, they have to go.
The Dremel Solution
I put an already used brown cutting disk in my Dremel. Use the thickest cutting disk you have. Don't forget to put your goggles on. Little pieces of orange plastic will be flying everywhere. My Dremel has a variable speed from 10.000RPM to 33.000RPM. I set the speed switch to the second "click". You shouldn't use too high speeds, 'cause then the plastic will melt.
First cut two groves through the tube parallel and flush with the flanges. Then cut the rest of the tube into "fingers" that are a little wider than the thickness of the cutting disk. Next cut right through the middle of each "finger". The last bits of plastic are removed by gently tilting the cutting disk a little. (N.B. Never tilt the cutting disk when working with harder materials! The disk could splinter and parts of it could lodge themself into vital parts of your anatomy.)
Use your fingers to remove all (almost) loose pieces of plasic. Then smooth out the surface of the remaining plastic ridge by running the cutting disk over it.
The Hand Tool Solution
First use a hacksaw to saw two groves through the tube parallel and flush with the flanges.
Then take some pliers. Use them to squeeze hard on the tube. It will break into pieces.
Lastly use a small file to smooth out the edges.
Using hand tools, it takes me less than half the time to open a corner, compared to using a rotary tool. Not to mention that with the Dremel you end up with pieces of orange plastic in your hair and all over the room.
If anybody has other ideas (Blow torch? Chainsaw?) how to open the corners, feel free to add them.
Don't take the text in this post to serious. I was bored this afternoon. But now we have pretty pictures to point too, when people ask about the "closed" corner problem.
Edit: Added 120mm to the title, as I saw several people on the forum think other sizes had closed corners too.