Sometimes, the plastic fan blade of a fan can be prone to breaking, rendering the fan useless, even though the motor is still able to run well. A non-functioning fan can be very inconvenient, especially when all you want to do is cool off on a hot summer day. So what now? Thankfully, it's quite easy to make your own fan blades out of cardboard.

In this tutorial I will show you how to craft my simple and efficient 2-blade design, but feel free to experiment with other designs of your own choosing (e.g. number of blades, shape, etc).

This is my 1st Instructable tutorial, so feel free to leave some feedback if you wish.

Step 1: Gather the Materials and Tools

These are the materials and tools you need to craft a cardboard fan blade.

Required materials and tools:

Cardboard of sufficient size (should be thin, and can hold its shape after bending it)
30 cm (12 inch) ruler
Pencil or pen
2 scissors (1 big, 1 small)
Drawing compass
Protractor
A fan (not shown)
Glue stick

Step 2: Design the Blades

In my case, I experimented with different fan designs to see which one would produce the most wind.

Depicted are 4 prototype fan blades.

This 4-blade one was my 1st attempt at making a cardboard fan blade. (the tape is to keep the blades at an optimum angle) I started out with a very large circular piece of cardboard about the same size as the final blade, drew perpendicular guide lines, and cut 4 slots on those lines, bending the sectors. Initially, the fan blade rotated slowly and hardly blew any air. Cutting out the sharp corners yielded the final result pictured, which blew more air than before. Unfortunately it was also a bit wobbly.
Same thing as the 4-blade one, only with 8 blades. Airflow was slightly less than the 4-blader. It also looks like a flower.
A 2-blade prototype. The idea came from the blade designs of some industrial fans. Although somewhat noisy, it was surprisingly capable of creating strong winds. Not too bad for something crafted from the side of a pizza box.
A refined version of the prototype, drawn using a ruler, drawing compass and protractor. (NOT crafted from the side of a pizza box this time.) The final design is based on this prototype.

From my experience it seems that with a motor that's already weak, the fewer the number of blades, the stronger the wind produced.

Step 3: Cut Out a Blank Square Piece of Cardboard to Work On

If you've got a pizza box, dissect it. Cut out the top bit (which is usually not oily). Else, just cut a square piece of cardboard out of a box, roughly the size of your fan.

Step 4: Draw the Design

The following instructions are for if you want to make my 2-bladed fan design. I have provided a schematic of my 2-blade design to make it easier to understand.

Divide the square piece of cardboard into 2 halves. You'll only need 1 half to craft my 2-blade design.
On 1 of the halves, find a centre point and draw 2 wide arcs opposite each other, with radius 16 cm.
Draw a straight line through the centre and the 2 arcs, using the ruler. This line should cross the 2 opposite arcs. Afterwards, draw another line at a 45 degree angle to the straight line.
On the angled line, draw 2 arcs on each side with radius 9 cm and 12.5 cm each.
Draw a circle with radius 4 cm at the centre. This will become the fan blade's hub.
Draw an arc with its centre at the outermost intersection, starting at the closer side of the centre circle.
Next, draw another arc with its centre at the other intersection, starting at the far side of the centre circle.
Repeat steps 6-7 on the other side. Afterwards, the outline of the collection of circles and arcs you've just drawn should look just like the schematic.

Step 5: Cut Out the Design

Now that the drawing is done, it's time to cut it out!

Step 6: Cut Out the Circular Blade 'hub' Parts

Draw 2 circles on the bits of the leftover cardboard from the previous step, then cut them out.

Step 7: Puncture Holes and Cut Slots

Now we need to find a way to puncture the holes in the blade, so that it can slip on the motor shaft easily.

Here's the method I used:

Measure the radius of the motor shaft.
Using this measurement, draw small circles in the centre of the 2 circular pieces and the main blade.
Using the sharp needle on your drawing compass, poke through one of the circular pieces on various spots in the mini circle you just drew.
Tear through the holes using the sharp needle.
Flip over and repeat steps 3-4.
Push out the unwanted little circle, and the hole is formed!
Repeat steps 3-6 for the other circular piece and the main fan blade.
You might want to fit it on the motor shaft just to check if it fits nicely.
To ensure the blade engages with the pin on the motor shaft, cut 2 slots opposite each other in the larger circular piece, as well as the main fan blade.

Step 8: Glue Them Together

Using the glue stick, glue the 2 circular pieces to the main fan blade, ensuring that the slots on the blade and the larger circle match up.

Step 9: Bend the Blades!

And the fan blade is done!

Step 10: Find a Way to Fix the Blade in Place

Since the final cardboard blade is much thinner than the plastic blade it replaced, the screw-on cap can't be used as-is without the blade disengaging with the motor shaft and slipping.

This is a simple cardboard retaining device that allows the screw-on cap to bridge the gap between cap and blade. What the device basically does is to help to hold the blade in place, acting as an extension of the plastic cap. I strongly recommend you create one of these.

The components of the device: 2 holders and 2 'sticks'.
The holes in the 2 holders can be made using the same techniques as shown in Step 7 earlier, while the 'sticks' are just simply rectangular pieces of cardboard of equal length, folded in half.