How is it so light and yet so strong?

Using the same "first principles thinking" that the brilliant Elon Musk gives credit to for his many novel and groundbreaking innovations, we redesigned the chair.

In Physics, there is a concept called Area Moment of Inertia.  You don't have to understand the details to understand the concept.  Basically, it is a method of calculating the resistance to forces applied to different cross-section shapes to determine which will provide the greatest stength in a given application. This teaches us that under many common loading conditions, material that is further away from the center of gravity of the cross-section is far more effective than the material near the center of gravity. It explains why a popsicle stick can be easily broken when flat but when rotated up ninety degrees takes on suprising strength. It also explains the shape of I-beams, bicycle frames and just about everything else you see that was designed by an engineer.

How much more effective is material that is further away from the neutral axis?  A lot more.  The moment of inertia is a function of the cube of the distance "d".  This difference is so dramatic that it makes the material that is close to the neutral axis insignificant by comparison.

So, why not remove it then?  

The 9611-010C Chair is completeley hollow. 1.27Kg

The 9611-010C Chair is completeley hollow. 1.27Kg

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Furniture Means Mobile

I am often asked what the purpose is of making a lightweight chair or table and I usually respond by saying how using less material makes it cheaper to make, ship or relocate. Sometimes I add some comments about sustainability or mention a quote like this one: "Art is the elimination of the unnecessary" - Pablo Picasso  .  But I always fail to mention that the word funiture and mobile are the same in many languages and the fact that mobility is the defining characteristic of funiture.   The word for funiture in Spanish is Muebles (moveables) Here are some other examples:

The word for furniture in French is meubles,  In Danish: møbler, Turkish: mobilya, Italian: mobili, Dutch: meubilair,  Swedish: möbler...you get the idea so lets get moving!

9611-008 Chair

9611-008 Chair

 




And...two more

The most visisble changes occuring now are in the back rest.  It is a stuggle to find the right mix of comfort, stength, weight and ease of assembly.  Revision "S" below is difficult to put together and isn't that comfortable. Revision "T" below it goes a long way to solving both of those problems but still needs a little more strength.  Back to the drawing board!

9611-009 RevS

9611-009 RevS

9611-009 Rev T, 1.32Kg

9611-009 Rev T, 1.32Kg

Fast Forward, Dinner for Eight

Chair Numbers two thru eight, each a one-of-a-kind experiment

Chair Numbers two thru eight, each a one-of-a-kind experiment

Hundreds of variations were attempted in this iterative process.  Each chair incorporates dozens of changes from the previous one as we changed the seat, back-rest, plywood material, experimented with lightening strategies and made structural revisions.  The chairs are shown in chronological order, with the closest being the oldest.  Each chair took about a week to design cut and assemble and the weight slowly dropped as we learned where we could remove material.

Gio Ponti's Superleggera

When I went to do some research on the subject, I found this chair that I was familiar with from my time as a vintage Modern furniture dealer but I had never purchased or even sat in one I also did not realize that this chair held the minimalist title of Lightest Wooden Chair tipping the scales at 1.7Kg.  Almost a full kilogram lighter than our first chair.

From Cassinas Web site: 

Design: 1951 - 7
Production: 1957 to the present
Manufacturer: Figli di Amedeo Cassina,
Meda, near Milan
Size: 82.5 x 40 x 44.5; seat height 45.5 cms
Material: varnished ash wood, Spanish cane

Ponti himself describes this chair as the “normal,” “true” chair, the “chair-chair devoid of adjectives.”1 With it, the architect pursued his own standard of keeping things to a bare minimum. At the same time, Ponti’s interest in classic forms finds expression in the chair, just as it does in his buildings. Ponti borrowed the concept for “Superleggera” (super-lightweight) from a series of simple, traditional chairs that have been produced since the nineteenth century in a plant near the Ligurian fishing village of Chiavari. Their stable, lightweight construction and low price made them extremely popular.

The Uber Leggera

For the last few months, we have been concentrating on making the lightest wooden chair in the world.  It all started when my my engineering school buddy, Jon Kipp came to Southern California for a shop visit. Ihad been working on the CNC cutting files for the chair for months but felt they were a long way from being ready to make something,  Jon said "What are you waiting for?  Lets build it!".  Jon is a great engineer, a brilliant problem solver and was ready to roll his up his sleeves.   It turns out I was right....and Jon was right too.  Forty eight hours later, after a number of work-arounds, redesigns and re-cuts, we were sitting in our first laser-cut plywood chair.  As the photo below on the right alludes, we were not sitting on it for too long before we discovered a weak spot.   But we made a chair! and it weighed only 2.6Kg...and that made me wonder: What is the lightest wooden chair in the world?