This translucent LED holding mid-section of a 25 mm thick computer fan replaces the original and converts a non-LED fan into an LED fan.

I first saw this on 2GuysTek's YouTube channel for modifying the Noctua NF-A12x25 fan and wanted to do my take on it.

Why do that? One can simply buy an LED fan…

Not only you can buy an LED fan, but you may also be able to buy an add-on LED ring for your existing fan, although the choices, especially for the ring, are limited.

I see three reasons for doing it yourself: 

1. You want to keep a specific fan (you like the brand, and/or it has some features not easily replaceable). I have an Arctic 80 mm fan with an extra socket for daisy-chaining other fans (PST series), which I wanted to keep. 
2. You want to have a specific LED strip (certain appearance, voltage, connection to the motherboard/controller). For my 4-pin 12-volt non-addressable motherboard RGB header and 80 mm fan, Speclux 5050 3-piece BS-SL014-54L-RGB kit fit well (with 300 mm strip length, it would be too short for larger fans). I wrapped one strip around the fan and glued two other strips inside the case. I will talk more about different LED types below.
3. You are looking for a project.

Types of LED strips

These days, entire components such as memory or graphics cards may come with built-in LEDs, communicating with the rest of the system via some protocol. For this project, we are only interested in LED strips, as they can be wrapped around the cooling fan. You will not be needing the double-sided glue tape that may come with the strip (I was able to remove mine), as the strip is wrapped around the fan frame “inside-out”, with lights shining inside the fan frame into the propeller. 

There are two popular types: 5 volts 3-pin and 12 volts 4-pin. 3-pin LEDs are individually addressable. While one part of a strip can display one color, another part can display a different color. Effects like “running light” or “color wave” are possible with 3-pin LEDs. 4-pin LEDs are non-addressable. You can still display the color you want, or do some simple effects like dimming or changing one color to another, but each individual LED on the strip will display the same color and brightness as the rest.

One can buy an LED kit that comes with wires already attached, splitters (there are usually more than one strip to be connected to one RGB header), and extension cables. This is convenient, but the length of the strip(s) in the kit may be insufficient for larger fans. Then, one can buy an LED strip on a reel (like in the video above). In such case, wire attachments are to be made manually (either with a soldering iron or with solder-less connectors). For example, for a 4-pin LED strip, search for “5050 RGB 4-pin led strip to power connector adapter”.

Computer LEDs need a matching controller to power them and render the desired lighting effects. A motherboard may have this controller built-in, in which case it will have the appropriate pins called RGB header. Another possibility is to use a separate LED controller that will be hidden somewhere inside the case. The lighting effects you see in the video above were possible because of the individually controlled LEDs.

Slicing the fan

The procedure I describe here will be slightly more involved than what you see in the video.

You will need a vise with protective jaw pads (especially if the jaws are serrated metal), a hack saw (a mini hack saw may be more convenient), sandpaper (100 and 220 grit), clear epoxy plus some time and patience, especially for sanding. It took me about an hour to hack-saw the fan and sand the parts.

Liberate the fan wire from the fan frame: you do not want to cut the wire while cutting the frame (pic. 1). Put on the protective jaw pads, if needed (pic. 2). Secure the fan in the vise. With a hack saw, carefully cut along the frame on the motor side first. Rotate the fan 90 degrees once one side is cut through. Do not cut deeper than necessary, or else you are risking nicking the fan blades. Once the motor is out, it will be easier to cut the second side (pic. 3).

Your goal is to separate the fan into three parts (pic. 4). You will be replacing the mid-section ring, but you will still need the other two parts. Wrap a piece of 100-grit sandpaper over a flat wooden stick and sand the surface until flat (pic. 5). Be careful around the fan blades. Repeat with 220 grit for a smoother appearance. The result will be a smooth leveled surface (pic. 6).

Printing the new mid-section ring

For the models I uploaded here, the wall thickness of the ring is set to match the original fan: 2.0 mm. At this wall thickness, print the ring from a translucent material. Atomic Filament, for one, offers several translucent PETG samples. I ended up preferring Translucent Smoke Black PETG over Crystal Clear PETG because it lets less light shine through the fan (although it strings like mad while printing). My LEDs are hooked up to a non-addressable type header on the motherboard (ASUS Prime B560M-K) with a lightning control app (ASUS AI Suite 3) that does not even allow adjusting the brightness. Blasting lots of static color through clear plastic felt overwhelming. I wanted to tone it down a bit. But your hardware and preferences may be different.

PETG is not the only material that can be translucent. So can be PLA, ABS, as well as more exotic PMMA and Polycarbonate. 

2GuysTek printed their ring from white, normally non-translucent PLA, but made it 0.5 mm thin for translucency. I raise my eyebrows seeing the walls this thin, but the bottom line is that you can customize the ring's wall thickness and other parameters by following the CAD link to Onshape at the bottom of this page. You do not need to know Onshape to do that, you only need to pick the values from the already-defined configurations.

Once you are on the Onshape page, look at the top left of the screen, where it says “Configurations”. These are lists of pre-defined parameters that modify the part. If the “Features” panel partly blocks them, position the mouse on top of the “Features” panel until the mouse pointer changes to the “slide” icon and drag the “Features” panel down a bit. This way you will be able to see all pre-defined configurations possible for this part. In particular, you should be able to see the following configurations:

• Fan Description - pick 80 mm, 92 mm, or 120 mm fan
• Wall Thickness - pick a value from 0.5 mm to 2.0 mm
• LED Slot Height (1 through 4) - pick a value from 2.0 mm to 7.0 mm. 

It is useful to be able to regulate LED Slot Height individually for all four LED slots. My LED strip, for example, is about 3 mm high. However, I want to tuck the leading end of it under the tail end, so I need one slot that is 2 * 3 mm = 6 mm. I also want to tuck the strip under the wires in the next two slots, and the wires are 1.5 mm high. So my slots are 3 mm, 4.5 mm, 4.5 mm and 6 mm in height.

For PETG, I found that I can avoid supports for slots up to and including 4 mm. Supports are hard to remove with PETG and they produce additional stringing. Avoid them if you can. If you must use supports, avoid putting them close to the walls: they will be hard to remove.

For the models I have uploaded here, 

• Fan Description=80 mm, 92 mm, or 120 mm
• Wall Thickness=2.0 mm
• LED Slot Height (1)=6 mm
• LED Slot Height (2 through 4)=3 mm.

In other words, I assume that you will be tucking one LED end under the other, but you will not be tucking it under any wires. Supports will be needed for a 6 mm high LED Slot. If I am wrong in my assumptions, go to Onshape and change the configurations to your liking.

To export the model from Onshape, first make sure that all things are configured as they should be. Then, right-click the "LED Mid-Section Ring” tab and select “Export…”. Choose “Format: STL”,  “STL Format: Binary”, “Units: Millimeter”, “Resolution: Fine”.

Note that the screw holes on the ring are not for holding screws: they are slightly larger than the screws. They are for ease of alignment when gluing the ring to the fan frame. The idea is that you put two screws diagonally into top and bottom fan plates and glue the ring using these screws as a guide.

The four cutouts at the screw hole posts are to allow for the wrapping of extra fan wire around the fan frame, turning it into a reel. The cutouts also allow for zip ties to tidy up and secure the wires.

Assembling the fan

The left picture (pic. 1) shows the mid-section ring printed with Translucent Smoke Black PETG. Notice how the LED strip is tucked under itself on top and under the wires on the right and bottom. 

The next step is to drive two screws diagonally into each plate of the fan frame. Drive the screws from the outside in (pic. 2), resulting in threads of the screws protruding on the inside (pic. 3).

Now that you have the parts ready, think in which orientation you want to glue them (pic. 4). When there was only one wire, it was possible to turn the fan 90, 180, or 270 degrees to select the best exit position for the fan wire. With both LED and fan wires, this will not be so simple after the parts are glued together since rotating the entire fan affects the exit position of both wires. Think of good exit positions for both of them now, while the parts can still be rotated independently before they are glued together.

I used 4 min clear epoxy to glue the parts (pic. 5), where “4 min” stands for maximum working time. I wish I had had a longer setting epoxy, with at least 15 min of working time. It is only possible to clean up the epoxy with mineral spirits while it is still fluid. 

The final result is shown of the right (pic. 6). Notice how the fan wire is wound around the frame and zip-tied to a corner.

CAD Link

https://cad.onshape.com/documents/7e776dbc4782c26d3a374ac3/w/19cf61b464ab037bb5dced2e/e/c32060d9a35f6c737621910b