Bent Plywood Chair

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I'm an inventor / maker / designer based in the Bay Area. My background is in residential archite...

Intro: Bent Plywood Chair

The Bent Plywood Chair is part of a broader study I'm up to experimenting with ergonomics- trying different materials and construction methods using the dimensions and posture of Mies van der Rohe's Barcelona Pavillion Chair (1929). This one is made using 3/4" plywood and kerf bending for smooth contours.

Step 1: Tools & Materials

Tools-

20V Black & Decker Matrix Driver

Black & Decker Matrix Circular Saw attachment

Black & Decker Matrix Jigsaw attachment

20V MAX* Lithium Drill/Driver with Autosense Technology

4-in-1 SmartSelect Multi Sander

•Various clamps

•Straight edge (I used a 5' aluminum level)

Materials-

•1X4'X8' sheet of 3/4" finish grade maple veneer plywood

•Wood stain

•Wood putty

•Satin spray-on Polyurethane

•Sandpaper, glue, spray adhesive, countersunk screws

•Paper template (4'X8' sheet)

Step 2: Design & Templates

I designed the chair in Fusion 360, which makes it very easy to swing back and forth from 2D to 3D. Fusion 360 is free for students and hobbyists, and there's a ton of educational support on it. If you want to learn to 3D model the kind of work I do, I think this is the best choice on the market. Click the links below to sign up:

Student/Educator

Hobbyist/Startup

When you open the file, you'll notice there are a lot of "sketches" plus the 3D parts. I used multiple sketches to design and alter the parts, then when I was satisfied with the design, I created new sketches derived from the finished parts to make the templates- to do this, you just click "create sketch" and select the face of the 3D part you want to cut out, and there's your template!

For the template layout, I nested the parts so that they would all fit on a single 4'X8' sheet. The solid lines are for cutting and the dashed lines serve as straight-edge guides. The offsets for the straight edge are equal do the distance from the edge of the tool guard to the side of the blade (it's the same on the circular saw attachment and the jigsaw attachment I used). That way I was able to clamp down the straight edge and easily make straight cuts.

Step 3: Cut Out the Pieces

I used super 45 spray adhesive to fix the template to the plywood. 45 is not as strong as 75 or 80, so it's easy to peel the template off without having to scrape or sand the surface.

The layout has the seat surfaces justified to the edges so that there's no need to cut those edges.

Using the circular saw attachment for straight lines and the jigsaw attachment for the curved lines, it took about 4 hours to cut out all the pieces.

I made perpendicular cuts to the tighter curves to keep the jigsaw from binding.

Step 4: Kerf Cuts: Geometry

Kerf bending is achieved by cutting through the plywood so that the last layer of underlying wood is left in tact. With multiple cuts made close together at regular intervals, you are able to bend the wood and create a smooth curve.

I chose to make the cuts at 1/8" intervals. Since the width of the circular saw blade is 1/16", you end up with alternating 1/16" solids and voids. This is very important too keep the kerf cuts from creasing when they're bent.

IMPORTANT: This particular circular saw attachment has a blade that's flat in its cut profile. If you were to use a different circular saw, make sure the blade you use is flat in profile (a Dado Blade for example). Many regular circular saw blades leave a "V" profile, which will make for an uneven distribution of force, and in my experience will make the wood crease.

ALSO IMPORTANT: The template layout I made assumes a crucial fact: that the veneer is oriented along the long side of the 4'X8' sheet. The orientation of the grain of the layers of wood on a sheet of plywood alternates. This means that the kerf cuts are made perpendicular to the last underlying layer of plywood- this also prevents creasing.

For the layout, I simply measured the length of the straight segments and arc lengths of the curved seat surfaces, adding the appropriate lines. In the curved segments, I added cut lines at 1/8" intervals as well as dashed lines outside of the cut areas to serve as guides for the cutting jig.

Step 5: Kerf Cutting: Jig

To keep the depth of the circular saw cut consistent, I made a jig out of some 1/8" thick poplar glued to "U" shaped ends to give me the offset I needed to leave that last layer of underlying plywood.

With a 1/4" gap in the center of the jig, I ensured that the offset from the blade to the side of the jig was exactly 2". That way, my offset guide lines allowed me to easily follow along with consistent offsets.

Step 6: Gluing and Sanding

The sides of the chair are double layers of plywood for stability. In order for the entire chair to be cut from one 4'X8' sheet of plywood, I had to cut one of these layers. As a result, I started with the whole side piece and glued the matching cut pieces to that.

Cutting by hand (at least my hand) doesn't make for particularly clean edges. I first sanded the edges of the whole side pieces, then glued and clamped the cut pieces to the more finely finished side.

Once the curved pieces were properly clamped to the surface, I added the screws in the rounded tabs on the seat and seat back pieces. With proper gluing and clamping, these screws don't really do anything to hold the chair together. Anyway, I like the look of them- they give one the impression that they're holding back the spring action of the bending, which in theory they would.

Once the glue cured, I sanded the entire profile of the double-layered chair side to make for smooth geometry.

Some other cleanup may be necessary at this stage. Make sure the rectangular channel in the chair side pieces are a consistent 1 1/2" so that the chair surfaces fit snugly.

Step 7: Finishing: 2 Options

I made 2 of these chairs, one with Minwax Classic Gray wood stain and spray-on Satin Polyurethane, and one with spray-on Satin Polyurethane only. I like the one with the natural wood color better, but the stain hides some of the imperfections.

The wood stain instructions advise brushing on the stain and leaving it for at least 5 minutes before wiping it off. I decided to wipe it off immediately because I thought this would leave more of the variation in the veneer surface visible. I think this also left me with a brighter color in the end.

On both chairs, I did 3 coats of spray-on polyurethane with 300 grit hand-sanding between the coats. The result is very smooth to the touch and helps a little with the veneer delaminating at the edges, which can happen with plywood that isn't edge-banded.

Step 8: Finished Product

This chair is incredibly sturdy, not too heavy, and pretty slick if I do say so myself. It's also pretty comfortable considering the lack of cushioning due to the posture of the chair.

One chair took about 16 hours total over 2 days taking sanding and finishing into account. It's also great exercise for kerf bending. Now go make one yourself!

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    48 Discussions

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    kbbaktha

    9 months ago

    brilliant. Kerf cutting magic.

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    T0BY

    1 year ago

    This is ace! What a great idea!

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    CarlosA120

    2 years ago

    Muchas gracias, estupendo proyetco!!!

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    KyleM5

    3 years ago on Introduction

    Thanks for this. Not sure if I understand what all the different patterns mean in the seat parts. The parts without lines are solid, the striped parts are kerfed, what are the "dashed" parts all about?

    1 reply
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    JON-A-TRONKyleM5

    Reply 3 years ago on Introduction

    Basically right. Solid lines are to be cut, dashed lines are an offset guide to make it easier to align a circular saw fence when doing multiple kerf cuts, dash-dot lines are offset guides to clamp a straight edge to when cutting the straight parts with a circular saw.

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    jfunderburk456

    3 years ago

    Hey mate, I like the chair a lot. I didn't know if you might know some of the angles and geometry of it. Such as the seat angle. I ask because I am cheap and don't really want to print out a giant template. Any help would be extremely appreciated. Cheers.

    3 replies

    I've added a jpeg with dimensions in step 2. Best of luck! I think you'd probably have a much easier time with it if you just paid the $20 and used templates, but I'm sure you're perfectly capable of making your own version with these dimensions. They're based on the Barcelona Pavilion chair, which has a very comfortable lounge posture.

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    jfunderburk456JON-A-TRON

    Reply 3 years ago

    Awesome. Yeah there's no where around me that prints anything that big. Most places will print engineering plans for around 20$ a piece but the biggest they go is 36"x48". So I figured I would try to draw it out using all the simple hand drafting tools. Thanks for the dimensions!

    There's always hand drafting- you'll get pretty much the same result either way. The great thing about doing it that way is that you can use the first part as a template for the duplicates...

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    DarrenP2

    3 years ago on Introduction

    HI man, mind if i redesign this for my Design and Technology Major Design Project at school/

    1 reply
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    JON-A-TRONDarrenP2

    Reply 3 years ago on Introduction

    On one condition- that you post an instructable! Keep me posted on your progress, I'd love to see what you're up to.

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    jeanniel1

    3 years ago on Introduction

    Oh, Man, your project is giving me ideas for several forms of furniture! Thanks for the DIY!

    1 reply
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    jfunderburk456

    3 years ago

    Hey mate, I like the chair a lot. I didn't know if you might know some of the angles and geometry of it. Such as the seat angle. I ask because I am cheap and don't really want to print out a giant template. Any help would be extremely appreciated. Cheers.

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    Making
    the reverse bend on the top of the backrest puts the most stress on
    the face veneer. Some advocate dampening to help induce flexibility,
    but another, more reliable solution is to apply compressive force to
    keep everything smoothly together until the glue dries. This can be
    done fairly easily using filament reinforced strapping tape, the kind
    used to bind packages and applied before the bend is made. It won't
    yield as the curve is introduced, causing the surface to remain
    intact while redirecting the forces internally, where they should be.
    This is an old installer's trick used when kerfing molding to go
    around staircase twist and turns and stopping surface blowout. It
    probably wouldn't hurt to do the same with the knee area waterfall
    edge too, although not as severe as the backrest top rail.

    http://www.uline.com/Grp_441/3M-Strapping-Tape

    Nice
    build too, by the way.

    4 replies

    So what you're saying is, first cover the area to be bent with reinforced tape, second bend and glue as usual, third remove the tape when the glue is dried and set? Thanks!

    That's essentially it, yes. It's been a while since I've done this trick, as I recall you want to remove the tape ASAP- it is shipping media, so tenacity is part of the formulation- it's virtue is also it's vice if you will, some heat may be helpful if it resists. Again, test on scrap first, today's ultra thin veneers may be problematic, good luck then.

    Where were you when I was making this! I tried to jury-rig something with ratchet straps for the same effect, but my straps weren't long enough to go all the way around. This is a great trick, I'll definitely try it next time.