This instructable shows how the wood inlay was created on the spine of this spiral staircase.
Step 1: Define a Design Parameter
There was a sculpture that functioned as a staircase that needed some help, so I happily obliged. After sculpting the inner curve, I had to create a look for the spine. I didn't know what it was going to look like but I knew how it needed to feel when you ran your hands down it. Based on the size of two hands together with overlapping thumbs, I played with different geometry in Sketchup. After seeing that the most efficient use of material would be to glue 3 pieces together, I realized that changing the direction of the middle piece would create a great contrasting color and texture. The end grain of wood always ends up darker than the face of a board so I used that to my advantage.
Step 2: Test the Design by Making a Prototype
After playing with the geometry in the computer it was time to test the hypothesis. I took some short pieces and glued them into long pieces. Then I sculpted them into a shape that felt good to my hands. I then cut it, stacked it, glued it, and clamped it, took a power planer to it, sanded it down, then darkened it with oil. I loved it. The concept was proven, now it was time for the real thing.
Step 3: Prepare for the Real Thing
I glued up long pieces of one size, then some more of a bigger size for the top and bottom. The staircase spine widens at the floor and when it grows into the ceiling. When I had all the long pieces I needed, I had to figure out how to attach them to the spine of the staircase. There had to be a precise notch cut into the bottom of the spine for the pieces to fit into. Now time for mechanical design.
Step 4: Design the Machine Needed for the Task
The notches I needed consisted of one vertical face and one horizontal face. I could more easily get the vertical face so I focused on that. A friend of mine let me borrow his giant beam saw, so I based my design off of having a single 17" blade to make the notches. Obviously, the saw had to travel back and forth, but it also had to move side to side and the angle would vary a bit. Each notch was slightly wedge shaped so I would need to have fine adjustment of both ends. I decided to use threaded rod for all linear motion.
Once the general concept was figured out, I borrowed some tools from friends, gathered scrap metal from wherever I could find it, and input all of those parts into a CAD program. The rails were 1"x1" box tubing and small pieces of cutting board served as low friction bearings. It didn't need to last long, only this project. With the CAD model figured, out I went to a friend's shop to fabricate the machine and test it's functionality. IT WORKED! I mounted a drill at one end of the machine, which turned a screw, which moved the saw! Very exciting stuff.
Step 5: Cut the Notches Into the Spine
With the machine complete it was time to put it to use. It took a while to get set up but once I had the process down it went pretty fast....sort of. The teak, mahogany, and epoxy dulled the blades FAST. Every 6 feet or so I had to get the blade sharpened. Also, doing it the way I did, where I made several cuts next to each other, took a lot of time. If I were to do it again I'd make a machine with two perpendicular blades.
Step 6: Glue and Sculpt Base Pieces
The next step was to clean up the notches with a power planer and glue in my small pieces. I started with the bottom of the spine where it meets the floor. It needed to be glued together as a section before gluing to the spine because otherwise, I wouldn't be able to get power tools in there to sculpt. Once it was installed, it was time to attach all of the other small pieces and glue them on. Just as the base was sculpted as a unit and attached, the top where it meets the ceiling needed the same treatment.
Step 7: Glue Blocks in Notches and Sculpt
It looked pretty cool with the stepped look and it got a lot of compliments.....but that wasn't what I was going for. Plus, it felt terrible to run your hands down! To smooth it out, I took a power planer to it and joined the curves. Then a belt sander, then a disc sander, then a random orbital. Months of planning, gluing, shaping, building machines, notching, and gluing all paid off. In about a day and a half, I was able to go from rough steps to final sanded spine, and it felt GREAT to touch!
It turned out better than I could have ever imagined and became my biggest achievement and helped me grow. The staircase was photographed for the Wall Street Journal and that photograph has made it onto countless design blogs and websites. I love to see how things are made and so I wanted to share this process with anyone whom it might inspire and educate. If it weren't for other people posting "how-to's" on the internet I wouldn't be able to do 25% of the things I do. I'm glad there is a place like this where we can collectively grow our knowledge base and become more capable humans!
Step 8: Other Notable Steps....
Getting to the spine phase was interesting too. There was a lot of out-of-the-box thinking that needed to happen. What was someone else's failed project turned into a really technical creative challenge for me and I loved every minute of it.
Here are some additional photos to tell the story.
For other photos, check out NickFournier.com