Introduction: Spine Chair
Digital design often clashes with traditional carpentry methods when attempted to be united. In this instructible I will cover the process I took to construct a wooden lounge chair with a form I generated using a Rhino - Grasshopper.
The lounge chair is comprised of 19 rib-like pieces of Cherry wood. The interstitial wedge components are made from 250 laser cut pieces of 1/4” Baltic birch plywood which were glulamed together. Ultimately the final fabrication process was done in less than two weeks.
The inspiration of this chair was derived from the structural makeup of a spinal cord and the formal aesthetics of a centipede.
Step 1: Stand Back From Your Design
The main focus for this lounge chair was to establish a comfortable profile. I was set on making it entirely from wood and using a CNC table would over complicate construction because all sides had complex curves. I had never really stood back from it to figure out how to go about constructing it but I knew I had to find a common point to measure from. The only consistent part of the design ironically was the profile I was obsessing about maintaining so it ended up being the registration vector I would use. Thought about how to use flat, traditional glue ups to achieve this radical form. Using this line as a reference, I was able to cut sections along the normal vector of all segments.
Step 2: Slice It Up
I first thought of how I could use flat wood pieces to establish a stacked lofted form. I used a straight forward method to splitting the wedges in Rhino. In layman's terms I simply created various planes oriented 1/4" apart vertically (This was the thickness of the wood I was planing on laser cutting for the whole chair)
Steps for slicing:
- SPLIT Command: Select Objects to Split (the lofted surface), then, Select Cutting Objects (Planes @ 1/4")
- DUPBORDER Command: Select the object you wish to extract the wire frame border from (each 1/4" slice)
Note: I incorporated a rectangular cut out on all layers to have a universal point to line up during the glue process.
Step 3: Organize and Label
To save myself some time, I rotated and aligned all the wedged pieces in a line to split them all at one, be careful if you don't have a powerful computer because this will easily crash it. (Mine is not exactly street legal). Once I went through all of the ribs and internal wedges I made sure to properly label them within the model. I organized the pieces into individual layers to help me lay out all of the parts onto the laser cut bed without losing track of any sections.
Step 4: Tessellating Pieces for Laser Cutting
I tessellated all the 2D slices with their designated label and rectangular cut out within the 24" X 18" rectangle that represented the laser bed. It is important to keep the pieces stacked and in their designated groups as you cut, I Saran wrapped each set as soon as they were complete so they wouldn't walk away and hid (Dexter style of course). With over 250 pieces, its easy to lose track of whole sets let alone singular pieces. For this particular project, any missing slice would have affected all of the aligned angled cuts that I needed to do later down the line.
Note: Be sure to clean the laser often, plywood will gunk up the lens which will mess with the factory line process.
Step 5: Time to Glue!
Now that I had all of the pieces cut and stacked, it was time for my favorite part - laying them all out in a line on a long shop table (Oh yes, picture time). Now before pouring out a single drop of glue I cut a few jig pieces to fit into the rectangle cut out I incorporated into each sliver. This 'rock-a-stack' method lets you effortlessly slide every slice of wood perfectly into place. This was key because wood glue ups are very unforgivable and tend to slide out of line very easily. This was especially needed because I had little time to glue up to 19 (double sided) pieces all together, while still leaving enough time left over for the clamp up without drying out. Water was the crucial factor here. Wood glue is slow to apply and quick to dry, but with a little water diluting it, it goes on really quick, doesn't dry out as fast and wont sacrifice any adhering strength. I used a glue brush but if you have a paint roller you're will to sacrifice, please do, at least for my sake, it will save you so much time and will be so utterly satisfying to apply.
Disclaimer: Sure you could just take your time and glue up less pieces at a time, but where the fun in that?
Step 6: Angle Cut Internal Segments (Hardest Step)
To keep the desired profile, I had to make sure to angle cut each segment with exact precision. With this method of stacking flat laser cut pieces of plywood, my best option was to use the table saw. That being said, this got a little dicey. Once I decided which side to register to the saw fence (the one that was used in the model) I had to eyeball the exact edge point the blade would begin to carve into the piece so that to not lose any material on its minimal side (seating surface side). Therefore I made sure to recalculate the angle according to this reference remembering that I really only had one shot at this.
Note: If you are't very familiar with using a table saw (or your first rodeo), this step is not an ideal method of cutting. But damn was it fun!
Step 7: Time to Grind and Sand (buckle Up)
This is the longest step. Unfortunately I do not have any images for this step because my wood shop was a complete dust cloud for roughly a week straight. Once I had all the pieces glued, they came out to be a very manageable in size for the grinding step. I was fortunate enough to have many different type of sanding weapons at my disposal for this step. I knew this was going to take a while and I did not want to sand more than I needed to so I made sure to use each tool to its best strength nothing more nothing less. I used the following tools in chronological order to go from rough grinding to fine surface smoothing:
1. Pneumatic chainsaw bit sander - Used to cut away the large unwanted 'stepped' look
2.Hand held wood grinder - Used to clean up rough work done by the chainsaw bit (previous step)
3. Oscillating table sander - Used to smooth down the pieces in a unified motion (let the machine do the work)
4. Pneumatic orbital hand sander - Used with a course grit to even out hard to reach areas
5. Hand held belt sander - Used for finalizing the sitting surface for a flush finish
6. Sand paper - Used in those hard to reach areas but also for an overall finish
Note: Make sure to be in a well ventilated space, I set up a vacuum tent, goggles, carbon face mask, ear plugs
Step 8: Time to Assemble
This part was a tricky process to figure out. With the standard clamps I had, I could only glue together 2 rib segments at a time because as the spine curved, the clamps would not register in the ideal flat manner. I decided to switch off between clamping and drilling screws to connect these pieces. for the most part this was pretty straight forward after I had thought of that obvious solution.
Step 9: Finishing Touches
The chair naturally did not sit right after completion. With 8 legs, it was hard to really expect it to. I used a Japanese "Kugihiki" Flush Cutting Hand Saw to even out all the bottom of the legs. (what a tool). I also made a point to hand sand the entire piece until there were no visual abrasions or any inconsistencies noticeable to the touch.
Here is the final product sitting in the Chelsea art Museum in New York City. I hope you enjoyed it!