CNC Scissor Chair (Plywood)

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About: Architect by training, Phil is a designer who codes. He abuses CNCs and industrial robots while building fine furniture, mixing digital fabrication and craftsmanship. He likes thinking about energy use with ...

Intro: 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!

Photo and this assembly video courtesy James McBennett of Fabsie (see first page for description). This is chair 2.0, which will become a part of a series of scissor chairs after the same design. Stay posted for more!





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    28 Discussions

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    ElleyS2

    14 days ago

    That looks amazing, a piece of art in itself!

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    pseatonlauren_hayter

    Answer 3 months ago

    The little angled pieces (see image with one of them in bold green).

    The semicircled corners are because the chair is intended to be cut with a router. Routers use round bits with some diameter (I think these are drawn assuming you cut with a 1/4" diameter bit), so if you just cut the edges of the square hole, the inside corners will be rounded and the matched part won't fit. The solution here is just to cut a little extra material to clear out the corner. You could also clear out the corners by hand with a chisel or special mortising bit, but those options require an extra step and a lot of extra time beyond just cutting the file on a CNC.

    I also like that the finished product shows signs of the process by which it was made, so the files as drawn assume the corners need to be cleared out.

    The same treatment is in all inside corners in the drawing, not just the small square holes.

    Screen Shot 2018-06-03 at 3.23.49 PM.png
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    pseatonlauren_hayter

    Answer 3 months ago

    The tests are exactly 1/4 scale in all dimensions: 1/4th the width, 1/4th the height, and 1/4th the length. So an example part measuring 8" x 2" x 1/2" on the finished chair would measure 2" x 1/2" x 1/8" on the 1:4 test.

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    amandaghassaei

    1 year ago

    whoa, I never saw this before, so cool phil!

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    HarrisonFilleul

    2 years ago

    Do you have these shapes in AutoCad?

    I want to make one of these as I have access to a CNC that runs on AutoCad/Microvellum.

    Cheers!

    2 replies
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    pseatonHarrisonFilleul

    Reply 2 years ago

    I've been hoping that by limiting this to students (.edu addresses), I'd have more luck getting photos of the finished products people make with the cad files. So far no luck so here's my request: if you use the files for anything, please upload an I Made It !

    Here are links to the CAD file, and some notes that I've gotten from feedback along the way:

    DXF: https://drive.google.com/file/d/0B6nIu9U60DlGeWZlV...

    Fab Notes: https://docs.google.com/document/d/1p6Q_mxhN5HZCWy...

    Note that the license for the CAD files is Creative Commons "Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0)", not the same as the license for the Instructable. You can't modify, sell, or distribute the files without permission. You must cite the author in any use.

    https://creativecommons.org/licenses/by-nc-nd/2.0/

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    buck2217

    3 years ago on Introduction

    Awesome , does it come in extra wide for the Mrs?

    (just kidding Darling, now put down that knife!!!)

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    Samw

    5 years ago on Introduction

    Hey this is great. I love the mechanics you use here. Is this an original design?

    1 reply
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    pseatonSamw

    Reply 5 years ago on Introduction

    It is, thank you! It's possible I'll have the chance to develop it a little further to make a "form family" of related furniture in connection with Fabsie (www.fabsie.com). This depends somewhat on the success of Fabsie's first venture, on kickstarter now -- https://www.instructables.com/id/This-Stool-Rocks/

    Thanks again!

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    mganpate

    6 years ago on Introduction

    very nice design but we are need the pdf pls share the details on mahesh.gan.143@gmail.com