Want to make your fan blow more wind? Or perhaps the fan blade has broken at the time you need it most! Never worry - it's easy to craft your own replacement blades out of cardboard.

In this tutorial I will show you how to craft my hub-and-blade design, building upon previous experience with cardboard fan blade design. After you're done, your fan will blow stronger wind than before!

Step 1: Background

After publishing my 1st cardboard fan blade design on Instructables, I continued experimenting, tweaking and creating new designs to see which one would produce the most wind. These are the results:

A 2-blade 'S' design, cut from a single piece of cardboard and the subject of my previous Instructable tutorial.
A 3-blade variation of the 'S' design. Performance was noticeably better than the 'S' blade, blowing a stronger wind. However, the limitations of the monocoque design became apparent over time, as the glued-together circular 'hub' parts loosened and came off due to stress forces. (later on, I installed computer screws to hold the blade together)
This was an experiment in reproducing the blade design that comes with the majority of electric fans around the world. It performed terribly, blowing less wind than the 'S' blade.
A trimmed version of blade #3, blowing slightly more wind than the 'S' blade.
Around this time, after reading some tutorials on DIY wind turbines (of which there are many), I experimented with a wind turbine made out of a Pringles can (blades) and its cap (the hub), mounted to a K'NEX tower, turning a small K'NEX wheel. It proved to be a good design, and was even able to winch up a small load when the wind was strong enough.
Close-up of the wind turbine. I used leftover computer screws from previous PC projects.
The success of the wind turbine gave me the idea to create a fan blade from multiple components, with a central hub and 4 blades screwed onto it. Performance was much better than all of the previous designs.
Designing the blades: I utilised a 'swept-forward' design, slightly widening from the centre to the tip, due to its ability to produce strong winds.

Eventually, I settled on a 3-bladed version of blade #7, which performs similarly to #7 and is less stressful to run for the motor. In this tutorial, I will show you how to make this particular design.

Step 2: Tools and Materials You'll Need

Here are the required materials and tools.

Materials:

An adequately sized piece of cardboard with dimensions 30cm * 30cm, which is able to hold its shape once bent
A fan (not shown)

Tools:

Glue stick
Pencil
Drawing compass
A sharp object (to be used for poking holes)
A ruler (optionally: 1 short ruler and 1 long ruler)
Screwdriver
Scissors
Retractable knife (to help with cutting)
Protractor
Set square
6 identical computer screws (I used 6-32 screws with 3mm diameter thread and 5-6mm length) or similar

Step 3: Prepare the 18 * 18cm Square Cardboard Piece

Before drawing the 1st blade, you need to prepare a square piece of cardboard to work on.

Draw a 18cm * 18cm square at 1 corner of your piece of cardboard.
Draw a horizontal parallel line across the square, 5.5cm down from the top-left corner. (From here onwards, I will refer to it as the 'centre line'.)
On the centre line, draw a 16.5cm arc with its centre at the left side.
Cut out the 18 * 18cm square cardboard piece. This is where you'll draw the shape of the 1st blade.

Step 4: Draw the 1st Blade

Next, it's time to draw the shape of the 1st blade. Don't worry - you'll only have to do this once, as you'll be using the 1st blade as a template for the other 2 blades. To assist with your drawing, I have provided a schematic of my blade design.

Draw the following points on the left side of the centre line at the indicated distance from the left edge. The pair of circled points are where the screws attaching the blade to the hub will go.
At the 0.5cm point, draw a perpendicular line.
On this perpendicular line, draw the following points at the given distance from the centre line.
From both points, draw new lines parallel to the centre line.
Next, draw the following points at the indicated distance from the vertical line (red) at the left.
At the 7.5cm point on the bottom line, draw a perpendicular line 9.5cm long.
Likewise, at the 10cm point on the top line, draw a perpendicular line 1cm long, before drawing back to the left part of the top line.
Draw an arc with its centre at the 9.5cm point at the bottom of the square, starting at the 7.5cm point on the bottom line.
Next, draw an arc with its centre at the 10.7cm point on the bottom line, starting at the triangle tip at the top of the square. After this, the collection of lines and arcs you've just drawn should look just like the schematic.

Step 5: Cut Out and Create Screw Holes in the 1st Blade

Once you've finished drawing, it's time to cut the blade out.

Use the retractable knife to slice an outline of the blade. This will make it easier to cut using a pair of scissors.
Cut the blade using the scissors.
Using the pointy end of the drawing compass, poke holes through the cardboard at the circled points.
Enlarge the holes using the sharp object (in this case I used a small Philips screwdriver).
As a test, screw in a screw in each hole and check if it does its job well. It should be tough to pull out when screwed in, and be easy to screw out.

Step 6: Draw and Cut Out the 2nd and 3rd Blades

Using the finished 1st blade, draw the outline of the 2nd blade on a remaining patch of cardboard.
To get the screw holes for the 2nd blade, draw inside the 1st blade's holes.
Repeat steps 1-2 on another free patch of cardboard to get the 3rd blade's outline.
Slice the outlines of both blades before cutting.
Cut out the 2nd and 3rd blades.
You might want to check that the distance between the screw holes is 2.5cm before poking.
Poke the screw holes in both blades.
Stack all 3 of them on top of each other and ensure that there are no differences in shape. If there are any differences, cut out the offending part. And you're done with the blades!

Step 7: Cut Out the Circles

With the blades done, you will now make the central hub that will hold the blades together. First of all, you need to cut out the circular pieces that will form the hub.

Draw a 6cm line and mark the centre on a large enough piece of cardboard.
On another piece of cardboard, draw two 8cm lines and mark their centres.
Draw a circle with 3cm radius at the centre of the 6cm line.
Draw two circles with 4cm radius at the centres of each 8cm line.
Cut out the circles.

Step 8: Draw the Screw Hole Pattern

On one of the 4cm circular pieces, you now need to draw the points where the screws will go. I have provided a schematic to show how.

On your chosen circular piece, draw 2 circles with radius 1cm and 3.5cm as shown.
Draw two lines 60° above and below the existing straight line. Ensure the lines are exactly 60° to prevent issues with balance later on. The intersections of the circles and lines are where the screw holes will go.

Step 9: Poke Required Holes and Cut Slots

Now, you need to find a way to drill the required holes in the circular pieces. This is the method I used:

Measure the diameter of the fan's motor shaft before we start 'drilling' holes. (For my fan, the motor shaft diameter was 7mm.)
Use this measurement to draw small circles at the centre of every cardboard circle. Remember: A diameter is 2 times the radius.
Many compasses have sharp needles, which we will exploit for our benefit. On one of the circular pieces, poke holes through the cardboard on the small circles you've just drawn, before tearing through them using the needle.
Repeat Step #3 on the other side.
Make one last final poke, and off it goes! Afterwards, repeat Steps #3-4 with the 2 other circles.
You might want to try to fit it on the motor shaft - if all went well, it should fit nicely without any loose feeling.
Once you're done with the holes, cut two slots 1cm long opposite each other on the 3cm and 4cm circular piece without the screw hole pattern.
Afterwards, on the circular piece with the screw hole pattern, draw a thick line perpendicular to the existing straight line. Once you're done, the circular pieces are ready to be glued together.

Step 10: Glue the Circular Pieces Together and Create Screw Holes

Time to glue the circular pieces together! You must glue them in the following order: 4cm with screw hole pattern on top, 4cm with slots in the middle, and 3cm with slots at the bottom.

Once you're done gluing them together, you might want to wait for at least 10 minutes depending on how fast your glue dries.

Next up, poke holes in the hub at the intersections of the circles and lines you drew earlier, using the same techniques you used for creating holes in the blades, and the hub is done!

Step 11: Fold the Fan Blades

Fold the blades one by one, before bundling them together and folding them upwards. For best performance, bend them until they are curved upwards when viewed from the side.

Step 12: Assemble the Complete Fan Blade

Get the 6 screws and screw the 3 blades to the hub one by one, and your fan blade is finished!

Step 13: The 'retaining Device'

Now that you're almost done, you need to find a way to bridge the gap between blade and screw-on cap - the blade can disengage with the pin on the motor and slip.

This is a cardboard 'retaining device' that I created to do just that, keeping the blade in position and reusing the original screw-on cap as well. It is made of 5 components: Two 'sticks', two 'holders' to hold the sticks together, and a 'washer' to prevent the 'sticks' from getting jammed within the screws on the fan blade. You may cut the holes using the same techniques as earlier.

Dimensions

'Holder' and 'washer': 3.5 * 2.0 cm
'Stick': 4.5 * 2.5 cm (depending on your fan, you might want to adjust the length of the 'stick')

Step 14: ...And That's It!

Now you can enjoy the rewards of your work and relax as the fan circulates air around your room.

Introduction: High Performance Cardboard Fan Blade