To make this key you will need:
- 1.5 (or just 2) 4' x 8' sheets of cardboard
- Plenty of hot glue and a hot glue gun
- Sharp razor blade with extra blades
- Long rulers/ straight edges
Step 1: Plan and Sketch
First, I (but you probably don't have to) sketched out how my final key would look. I decided to scale my key up so that every 1/32 of an inch on the original key would become 1 inch of cardboard key. Since the original key is 2 1/8 inches long, the cardboard key would be 68 inches long. In my sketches below, I include the final dimensions of the cardboard key, as well as how to layout your sheet of cardboard to maximize its use. I forgot to note in my drawings that the thickness of the key will be 2 inches as shown in the last picture.
After laying out your drawings, it is time to scale them up and onto the cardboard. The easiest way I found is to divide up the cardboard into chunks as shown in the smaller drawings. For example, the key "head" is shown in the drawings as being 32" x 28", so simply draw a rectangle on the cardboard that is the same size. After you have drawn out all of the basic shapes with rectangles, then go back in to put in the details such as rounded corners or the teeth of the key. After your first key is drawn and you feel happy with it, it is time to cut.
Important: When dealing with corrugated cardboard, it is necessary to take note of the direction of the corrugation. In this case, we want the corrugation to run perpendicular to length of the key faces.
Step 2: Slice and Dice
Safety Steve Says: Please be careful, razor blades are razor-sharp(duh). Use with extreme caution.
The 'key' to making kickin' cardboard objects is the miter joint. This is preferable to the butt joint, especially in the case of cardboard because the miter joint won't show the corrugation inside. Seeing the corrugation is what makes cardboard things really look like cardboard (cheap looking). To do this, every cut needs to be made with the blade at 45° or less. This is when it becomes very important that your razor is brand new and very sharp.
Otherwise, this step is fairly simple. Cut out your drawn key while maintaining a blade angle of 45°.
While cutting this way, you will create a piece of cardboard with a larger side and slightly smaller side. The larger side will always be the outside of your object so remember to cut 45° from the proper side.
After cutting out the first face of the key, you can use it as a template to trace the other side and then cut it out as well.
Step 3: Prepping the Grooves
Now that both key faces are cut out, it's time to cut the grooves. To get them ready, you just need to cut parallel slits down the length of the 'tail' of the key. One side (shown) has two grooves, and the other side has one 1" groove that fits in between the high point on the opposite side.
Step 4: Gluing the Grooves
First you will want to get the grooves of one side completely glued. Because the total thickness of the key is 2", each strip of cardboard used in the grooves will be 1" wide. Cut several long 1" strips of cardboard using the 45° cutting method and glue them into their appropriate locations. To glue the 1" strips in where the groove curves, I took off 2 of the 3 layers of cardboard from the backside, put glue on it, and slid it into place and kept it square. If everything was straight, however, I kept with the miter joint method.
Only glue the grooves to one side at this point.
Step 5: Completing One Side
What is great about cardboard is that if you take a ply off of one side, you can create very smooth curves. This is what we need to do to create the walls or thickness of the key.
Cut several 2" wide strips across the grain (as shown) using the same 45° method. Try to get strips as long as you can make. After cutting the strips to the right size, peel off the inside layer of paper while keeping the outside and corrugation. You may not need to take off the paper on every edge (some edges are straight) but you couldn't go wrong doing so.
After your strips are cut and floppy, work your way around the outside, gluing the 2" strips to your base (the face that has the grooves glued). Remember that where the teeth of the key are you will have to make the strips 1" wide instead of 2".
If your strip is not long enough, simply tear the two inside plies out of the last half inch. Then you can glue the single ply on top of the beginning of the next strip to make for a seamless look.
This would also be a good time to add a few support pieces to the inside. I made tiny triangles whose width is 2" minus the thickness of two sheets of cardboard. I believe cardboard is 1/4" thick so each support would be 1 1/2" wide. Glue these inside wherever you think it necessary.
Step 6: Add 2nd Face
Attaching the final piece is fairly simple but requires one trick: scoring the face into segments. Before attaching the face, make several scores (cuts through 1 ply, along corrugation) into it. Then, when gluing, attach only one of the segments at a time while keeping the others folded back. Slowly work your way from the head of the key down to the tail.
When you reach the end of the grooves, you will notice that the cardboard is different lengths. You will have to carefully trim everything down to the right length before finally attaching it.
Step 7: Done!
Now you are done! Enjoy your giant key! Take it on the city bus with you!