Pi Chair - She Was Born on Pi Day (so Was Albert Einstein)

A Pi Contest, how could I pass that up?

So got me thinking, what could I do that would be interesting and unique? Of course I thought of circular and Pi/Pie things but since I was already "piecing together" a puzzle chair idea , why not make a Pi Puzzle Chair?(that's 2 puns btw) Plus, it would be a nice gift for a Pi Birthday.

I went through a view design cycles until I came up with something I liked. I'll share my process below along with an interactive 3D tinker cad model that you can explore in more detail.

The best part of the final design is its rather simple (which I liked).

You can make it with basic tools and I hope you try yourself.

Pretty Basic, right?

1. 3/4 Marine grade plywood (my board dimensions were 12" x 36" but you can size or supersize as needed)
2. A Scroll Saw (or you can use a coping saw and a sanding block to round the edges).
3. A Hand Saw and wood file (or more sand paper)

First, I had come up with ideas on how to design the Pi Chair and then how to build it. My constraints were to have no more than 4-6 main pieces. Also, I wanted it easy to manufacture and ship.

My first attempt had a full circle for the chair back and half circles for the sides, but for the seat, I thought it would be interesting to use a triangular piece to look like a slice of pie. I even created little pie wedges to lock the seat in.

This design turned out not to work well when I built a paper model (you'll see in the next step). So I went with an all circular design and that turned out well.

Have fun navigating around the tinker cad model to explore. Tinker cad is useful to quickly try out design ideas.

Next, I built paper models of my tinker cad designs. You can see the challenges with the "pie" seat concept and why I abandoned. (Maybe you'll have better luck since I still like the idea.)

The all circle design had more potential and I decided to change it a bit. Instead of having the seat fit into a back slot, I had the back fit into a slot in the seat which made it easier to assemble and it added strength to the back.

The design was now locked down.

Here, I created 2D models of all parts. The diameter of the circles was ~12". For the side angles, I played around in tinker cad on what looked nice.

Once I settled on that, I used a compass to draw out the circles and then marked out the cut out areas for slotting the pieced together like a simple little puzzle.

I hadn't used my scroll saw that much but is was surprisingly easy and fast to cut out the parts. TIP: One key thing is use the seat back to mark out the side notches to fit in the back correctly with the right angles. You may need to use a file to tweak thinks a bit (I did). You can also gauge where to cut the slot on the seat bottom. Finally, I created a wedge to help locked the sides to the seat,

To make it more obvious it was Pi chair, I used the scroll saw to cut a Pi symbol in the seat back. Experiment: I learned a new technique (at least for me). If you tilt the scroll saw around 5 degrees and then cut the Pi shape, you can make the cut part sink (or pop) away from the background. That was a nice learning.

This was the fun part. Just slide the seat bottom into the sides. Wiggle the sides around to align the seat back to the side notches. Insert the seat back into the side notches and seat bottom so everything fits nicely and locks into place. The back is very sturdy to easily support a child's back.

That's it. I spent more time on the design then the actual build but to me that is the fun part. Maybe next step is to make it a rocking Pi Chair (but that might get messy).

Go ahead and try it yourself.