Introduction: CNC Scissor Chair (Plywood)
CNC + plywood = furniture. Search instructables and you'll come up with over 47,000 results for "CNC furniture." But for the great majority of CNC machines -- the 2-1/2 axis CNC routers that can move only in X, Y, and Z (no tilting or rotating controllers) -- a very specific condition has come to be part of almost all projects that result: the orthogonal joint. The orthogonal joint, essentially a product of the needs for tightly-fitting "notches" to fit together with friction, is a defining characteristic of furniture made this way.
This project, the "Scissor Chair," takes its design inspiration from the non-orthogonal joint cut on a machine capable of cutting only orthogonal (non-beveled) profiles. The finished chair is as purely a CNC project as I could manage: it requires exactly one sheet of standard 1/2" plywood, no extra parts, no hardware, no glue, and no other tools (except maybe a mallet to show it who's boss).
The Scissor Chair will be one of the first chairs available for purchase through Fabsie, a new website aimed at letting people buy highly designed small-run furniture anywhere in the world by connecting buyers with local fabbers and digital designers from all over. James McBennett, Fabsie's founder, made the world's second scissor chair. He is working to smooth out the fabrication process to open up the design everywhere!
More and larger photos are available on my website, http://www.phil-seaton.com (click "Scissor Chair" once you get there). I will share the DXF files with anyone emailing from an academic email (".edu"); in exchange I ask that you send back photos of your process and finished chair, and tell me about any snags you hit while making it. The goal is to iron out problems people encounter during the making process: if you get the file, that's not license to distribute or sell the file or the finished chair.
Step 1: Scissor Plan
From the top (plan) view, the final chair's design rests on the complex joinery required to allow planar sheets to intersect in this way.
Step 2: Joint Studies
For this orthogonal-but-not orthogonal design, a series of oblique joints with straight cuts served as generative components for the chair. Tight friction-fit joints are maintained oblique parts. The joint on the right side was abandoned later as the design evolved more purely towards the "scissor" plan.
Step 3: Design Considerations
The design assumes a perfect "scissor" plan / top view. Variations of the "tightness" of the scissor joint and the chair's profile serve to produce several design iterations on the same principle.
Step 4: Scale Models
1:4 tests were lasercut to test the structure and design of the chair. The 1/8" thick masonite makes it possible to exactly test the joint's tightness of fit: The files are scaled down to 25%, and the material is exactly 25% the thickness of the final 1/2" ply.
Step 5: Assembly Diagram
Step 6: Cut Sheets
The entire chair is cut from exactly one full 4x8' sheet of 1/2" ply. Details in the final file cut corners wide to allow space for a 1/8" router bit to profile cut without destroying the geometry.
Step 7: On the CNC, and Then, Glue-free Assembly!
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