Designing a Functional Cardboard Chair

Hey Guys!

In this Instructable I will walk you guys through the design and build process of making a cardboard chair. This project was an assignment to me in design school, but it is a fun, cheap design challenge that really got me thinking about how to make chairs.

Things you'll need:

Corrugated Cardboard: You might have to go searching around for suitable cardboard sources or have to be creative with your design to fit your Cardboard's limitations. I was able to make mine with two 8'x4' sheets of cardboard and one double layered card board box I found from Home Depot.

Hot Glue: to reinforce the connections.

Box Cutting Knife: Because you know, we are cutting boxes and stuff. You can actually use whatever knife you are most comfortable cutting cardboard with.

Let's Get Designing!

Step 1: Prototyping

For this first step, use scrap cardboard. You will go through a lot of it probably and you will want to save your good quality cardboard for later.

Making a Plan:

The most important part of any build is the prototyping phase. For this project I actually only spent two hours designing building the chair and from those two hours I learned so much. In the short time span that I had to do things it made the decision making process really quick. I decided the main seat and footprint of my chair would be the trapezoid shape that my legs make when I am sitting relaxed. So using a friend of similar size to me I measured the outer corners of the knees to be the base of the trapazoid and the width of his butt to be the top of the trapezoid. I did a quick search on the internet on my phone and found that crossing two pieces of cardboard with a slot in between them helped improve the structure of cardboard for architecture models and such. So I calculated the lengths of all the sides of the chair and the cross members that go inside the trapezoid seat so I had the size of all my cardboard pieces.

Building The Prototype:

Still adhering to my two hour time constraint I started to assemble the chair and realized quite a few things very quickly. First of all: Make sure the corrugation of the cardboard is perpendicular to the floor. I discovered that card board is really only strong at supporting weight when the weight is applied perpendicularly to the corrugation, otherwise the cardboard will fold in on itself. Remember moving boxes? Their corrugation runs straight up and down for this reason, so you can stack boxes on top of each other.

Other than that fun discovery, assembly of the prototype went smoothly. I discovered that really only the two sides were needed to help keep the crossed pieces at the right angles and I didnt need to do anything on the back or front. This allowed me to make a cut out for the legs to make it easier to get out of the chair as well as add an impromptu backing to the chair. At the end, the seat was hot glued to the base work and hot glue was ran down all the slotted joints to keep them together.

Result:

The chair was a great success. It was able to support all of my weight and even my friend standing on it. Now I have the basis for a card board chair design.

Step 2: Refining, Then Designing

This step is just as important as (if not more than) the prototyping step. This step refine you idea more to what you want your chair to look like and include details that would make things more comfortable. It is important to come up with final dimensions of all your pieces so that you do not waste any quality card board on this build. I'll show you what I came up with and how I came to those conclusions.

Applying Discoveries:

Inadvertently I made a design that is extremely good at supporting a sitting person. I initially made the trapazoid seat to reflect the shape my legs make when I sit comfortably; how ever, using the crossed pieces method i realized by making it a trapazoid the geometry moved that intersection up towards the back of the seat, where my butt (and most of my weight) was pressing down on, and there for giving me the most support right where I needed it.

Look at other chairs for inspiration. I looked to other chairs for better dimensions for my chair; cafeteria chairs at my college were pretty good examples because they were chairs that were brought down to their simplest form in order to be cheaply made. From looking at those chairs, I found that a slight decline in the seat and the back rest being a right angle to the seat was a change that could really support the comfort of the chair. In addition to the decline, I saw that the back corner of the chair kind of hugged and supported the human form at a place where there might be an awkward uncomfortable corner. Last major dimensional change I made was the support for the backrest. Instead of the previous design where it was perpendicular to the floor and wobbled a lot, I actually mirrored the angle of the recline to be the angle at which the support interacted with the back rest. In the final design this proved to be enough.

You can see all my final dimensions and the design I was aiming for in the picture above.

Step 3: Cutting Out and Assembling the Base

This step is fairly self explanatory. Draw your pieces out to the refined dimensions you had in the step prior with a sharpie then cut the shape out with your box cutting knife. When slotting the two halves together make sure the slot are on opposite sides of the cardboard, so on one piece the slot comes from the top on the other the slot comes from the bottom. Also make sure the slot is at least the width of the cardboard. When Making a fold, cut only halfway through the cardboard which will create a crease that will make it easy to get a sharp fold. As a final step, run hot glue along all the intersections of the chair to make sure they do not come apart. when you move the chair around. And most importantly of this step again: Make sure you are cutting the pieces so that the direction of the corrugation is perpendicular to the floor.

Step 4: Adding the Seat

This chair would only be comfortable if it had something to sit on. So I drew out the dimensions of the trapezoidal seat and backing onto my box of double layered cardboard from Home Depot, cut them out and hot glued them to the base. Now I was going to put one more layer over the top the Home Depot box to connect the back rest and the seat together and have that form fitting support in the corner; but, to make sure that form fitting curve didnt tear if it took too much of a load I rolled up a piece of scrap card board to provide that extra bit of support.

Lastly adding that final layer to the seat. Repeating the process of drawing out and cutting the piece out, I hot glued it to the home depot seat. I made sure to leave a little excess in the top layer to fold over and cover the corrugated ends of the Home Depot cardboard for aesthetic reasons. For this layer I purposefully made sure that the corrugation of this piece was running in a perpendicular direction of the corrugation of the Home Depot cardboard. I believe this is what they do in ply wood to help distribute the pressure, by making sure the grain of the wood runs perpendicular to the previous ply's grain, so hopefully that same concept applies in cardboard.

Step 5: And We're Done!

So those were all the steps I took in creating this cardboard chair. It was a very organic process, I tried to do it to a certain level of exactness but as it was a school project it was supposed to be a learning experience. Over all it was a pretty good result; it turned out extremely sturdy, more than enough to hold my 200 lbs so it was a success for me!

I hope this helps people prototype chairs that they might want to make out of wood, or helps people with creating unique items of cardboard furniture, or maybe even design students who have to do this project as well for their college design classes, I hope this helps you all!

Thanks for reading!