SHARKCHAIR: Modular Interlocking Furniture Design

Hello fellow instructable, CNC, shark, or furniture enthusiasts! In this instructable, you will learn how the hottest piece of furniture to ever be publicized was created, but first how about I tell you a story, the story of the SHARKCHAIR.

This story begins with two best friends charged with a task, to create the functional piece of art known worldwide as SHARKCHAIR. These friends jump at any opportunity to use machines for any manufacturing purpose, so this assignment generated a lot of excitement for them. The class they were currently in was called IED and was part of the PLTW pathway. Generally this class deals with 3D design on various computer software programs, however their teacher liked to push the boundaries of the curriculum and allowed them to do this project.

One year later, with the release of the CNC contest, those same boys decided to dust off their engineering notebooks, boot up their old files and create a new chair, a SHARKCHAIR 2.0.

Step 1: Design Requirements

With any assignment, there were a few requirements.

- It all had to fit on a single ¾” 4’x8’ sheet of oak plywood.
- It had to be as the project name suggested, a “Modular Interlocking Furniture Design”.
- This meant no glue, no screws, and no fasteners of any kind.
- We also were awarded for having as little waste as possible in our leftover board.

Step 2: Inspiration

We took many things into consideration when designing this. Our first thought was: “What would set us aside from our classmates in our teacher’s eyes?” Our teacher’s, as well as our favorite super hero is Batman, so we created concept sketches for a bat throne. Shortly after we realized this throne fit for the Dark Knight would exceed our allotted wood by one to two boards, we scrapped that and began to think of new ideas. Some research later and we created a list of design ideas we wanted to include in our design, such ideas as a sleek open design on the bottom, like a cantilever (for possible storage of notebooks), and as few support beams as possible while still offering substantial support. For some reason still unknown as of today, we chose to add shark fins to the top of the chair. Fortunately this was implemented into the final design, seeing as how it created an identity for the chair, setting it aside from all other chairs to be produced within that class.

Step 3: Designing

The design process took the longest on the chair since we had many things to consider.

- Comfort: We analyzed multiple different pressure maps of the human body while sitting in order to create curvature in our rail pieces in ideal places.

- Aesthetics: Of course the uniqueness of the design is what gives it its iconic name, SHARKCHAIR.

- Functionality: A good design is nothing if it can never be executed. With our design, we still had to take into consideration the interlocking part of the requirements.
- For our interlocking joints, we created ¾” x 1.5” slits in our 3” rails as well as the same size slit in the corresponding support. This allowed the top of the rail to sit nearly flush with the top of the support.
- When considering curvature of the rails, we first aligned the two corresponding points on the outside support and the inner 1” offset in the middle support. Then, measuring the distance between the two points, we adjusted that to create each rail.

Step 4: Final DWG

Once all the pieces were designed, we fitted them, tediously, into a 4’ x 8’ window to be transferred to Mastercam. We realized that, with the extra space we had, we could fit something else into the waste material. So we added a foot rest, and to our benefit, it cut back on our waste problem while adding something more to the design.

Step 5: Toolpath

We used Mastercam X8 to create our toolpath, then set Shopsabre as our machine type.

**NOTE** When designing our SHARKCHAIR 2.0 we encountered a problem when it came to the shark fin cup holders, we selected all the pieces of it at once. This cut out the cup holder in a weird order, outside to inside, leaving the piece free to move about as the router cut the inside parts. So we ended up with a mangled cup holder and connector joint, luckily this was easily taken care of later. So the moral of this story is go inside to out when creating toolpaths.

Step 6: Make Friends With Your Local Wood Supplier

For the first SHARKCHAIR, the wood was supplied by the teacher. For SHARKCHAIR 2.0, we made a deal with our school’s woodshop teacher so we could get the wood provided for us. This probably won’t work for everyone so if need be, you might have to dish out a few bucks for wood.

Step 7: CNC Cutout

This is where all the hard work and hours of designing and redesigning finally paid off. When that first cut sliced through the wood like butter, it brought a whole new reality to the chair. What was once a bunch of sketches in a notebook and drawings on a computer had been carved into existence.

Step 8: Assembly

Due to the variance in the size of the wood, not much sanding was needed to get it to fit straight off the CNC machine (The designed joints were 0.75” and the actual thickness was around 0.72”. This gave us some natural tolerances.).

All finishes should be applied when disassembled, extra sanding is definitely a possibility.

Step 9: Final Thoughts/ Comments

Our Original SHARKCHAIR was taken to WSU to compete in their Spring Showcase for IED classes. We took first out of all the IED classes there and gained some nice bragging rights against the upperclassmen in our class. All in all we were very grateful to have been given the opportunity to push and ultimately exceed the required material for that class as well as learn to use the CNC machine and everything that comes along with that.

So now you know the story of two boys and how they created the iconic SHARKCHAIR, learning the skills to one day master the trade of manufacturing. If you enjoyed it please vote and help us reach this level of mastery.