Introduction: Bent Plywood Chair

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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!

Comments

T0BY (author)2016-11-28

This is ace! What a great idea!

CarlosA120 (author)2015-12-10

Muchas gracias, estupendo proyetco!!!

DaniloB1 (author)2015-02-25

:) Muy buen proyecto!

KyleM5 (author)2015-01-05

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?

JON-A-TRON (author)KyleM52015-01-05

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.

jfunderburk456 (author)2014-11-24

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.

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.

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...

DarrenP2 (author)2014-11-25

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

JON-A-TRON (author)DarrenP22014-11-25

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

jeanniel1 (author)2014-11-23

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

JON-A-TRON (author)jeanniel12014-11-24

Awesome! I hope you post what you make-

jfunderburk456 (author)2014-11-24

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.

BeachsideHank (author)2014-11-19

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.

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.

Awesome, makes sense, thanks for the reply.

JON-A-TRON (author)BeachsideHank2014-11-20

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.

BeachsideHank (author)JON-A-TRON2014-11-20

Bending plywood shapes is especially risky today, with their micro- thin face veneers that dominate the market. Furniture factories would use a combination of steam and pressure plates to good effect, but for the small shop guy doing one- offs, you have to get inventive. The only other option is to vacuum veneer or hot hide glue the finished surface, but those methods are a whole 'nother Instructable, what you have shown is that it's doable if one takes care as you have done. Again, nice work.

legionmanchild (author)2014-11-24

What did you use to fill the kerfed gaps for finishing? I recently finished a table and filled the gaps with DAP stainable wood filler and was bummed at the result. The woodfiller didnt take the stain nearly as well as the wood did and pretty well ruined the project. Thoughts?

I used Elmer's Stainable Wood Filler and was also really bummed with the result. It's less noticeable with the gray stained version, but that's only because the wood filler already has a gray tint.

The best way to make wood filler in my experience is to collect the sawdust from the wood you're using and mix that with wood glue- you end up with a filler that's the same color as the wood. This is tough with plywood though- it's only the veneer color that you want to keep. It also probably doesn't take stain very well since there's so much glue in the mix, but it's worth a try.

I think using something that will contrast with the wood would come out really nice. Maybe even red Bondo. The trouble with this one is that since I used cheap plywood, the leftover ribs from the kerf cuts break apart very easily. If you use high quality plywood, the layers will be strong enough to stay in tact, then a contrasting filling would look nice

nathanaloysiusbash (author)2014-11-24

Slick chair. Love the fact that you cut slits to bend the wood. What is that music in the video?

That's stock audio our videographer found! Not bad right?

Beautiful song, Nice chord progression, just the right amount of stuff going on.

Wingloader (author)2014-11-24

Beautiful.

jpetritus (author)2014-11-23

Where did you get the template printed?

JON-A-TRON (author)jpetritus2014-11-24

We have a large format plotter at the pier, but you can get stuff this size printed at any print shop that does plans for architects and builders. Kinko's almost always has large format printers that can do 48" wide prints in my experience. You can always tile smaller prints if no one in town has a printer that can do a 48" wide roll- I've done that many times.

drhatch (author)2014-11-23

Great Instructable!

You said "kerf cuts are made perpendicular to the last underlying layer of plywood" but it looks like the kerf cuts were made parallel with the the grain of the top (uncut) layer of plywood. Am I reading it wrong?

JON-A-TRON (author)drhatch2014-11-24

My wording is probably a bit confusing. The top (uncut) layer, as you put it, is very thin- it's the fish veneer. The last underlying layer beneath the top uncut layer is the one you need to rely on to keep the veneer from splitting. Since the grains alternate with each layer, your cuts have to be perpendicular to the last (also uncut) underlying layer, which makes the cuts parallel to the uncut top layer.

father jack hackett (author)2014-11-23

I use this to make drum shells

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0CEYQFjAG&url=http%3A%2F%2Fwww.technologystudent.com%2Fdespro_flsh%2Fflexply1.html&ei=td9xVMzJEMLcao-BgvAP&usg=AFQjCNFGnIzjLeDvf1gdxRobsovF8ARiLA&bvm=bv.80185997,d.d2s

I've seen this stuff used before- It's perfect for lamination. I would think you'd spend a lot more time on jigs, but you wouldn't have to make all those repetitive cuts. I've seen people make big jigs out of MDF and crank out multiple pieces using this stuff. The cool thing about it is that you can do both convex and concave curves and end up with a smooth wood surface. It's like the light version of molded plywood ala the Eameses.

mc2517 (author)2014-11-23

Very crafty and inventive. There is a bendable plywood available-- might be more expensive but less labor intensive. This would enable a "skin" to be single piece and perhaps more curvy.

JON-A-TRON (author)mc25172014-11-23

This stuff has been suggested to me before as a non-structural finish. Not sure how sturdy it would be with this design, but I'm sure it would do the trick with a little more reinforcing. It would certainly be easier than making all those kerf cuts!

Zach.Ogilvie (author)2014-11-23

I really want to make this but my cordless drill is a Makita, not a Black & Decker. Will it still work? Please let me know. Thanks!

JON-A-TRON (author)Zach.Ogilvie2014-11-23

Hm... I don't know about that...

G10768 (author)2014-11-23

Definitely going to take this challenge to make this chair. Any chance you can tweek the design to add arm rests like an adirondack chair?

JON-A-TRON (author)G107682014-11-23

This would make a really good adirondack chair as a matter of fact. The posture is already there. That would make an easy first project in Fusion 360! After a few beginner tutorials, you should be perfectly capable of adding arm rests. Please show me what you come up with!

MattTheMaker (author)2014-11-20

I've done kerfing on larger transitions for a skate ramps before but never had to wrap around a radius that tight, great job! Glad to know that can be done, thanks!

JON-A-TRON (author)MattTheMaker2014-11-20

To be honest, I wasn't sure it was going to work with 3" radius- I don't recall ever seeing that done in plywood. But it worked just fine with no blowouts!

wavelet_spaghetti (author)2014-11-19

gorgeous design and finish... especially in natural wood.

Thanks! the natural one come out looking good, but the one with the stain covered the putty on the kerf cuts better.

tomatoskins (author)2014-11-19

That reminds me of my years of wood shop in high school! I love it!

JON-A-TRON (author)tomatoskins2014-11-19

You were so lucky to have woodshop in high school! I've been DIY my whole life, a real instructor at some point would have put me way ahead.

tomatoskins (author)JON-A-TRON2014-11-19

Yeah, I was really lucky! I had 4 years of wood shop and 4 years of electronics in high school. I was really sad that I never had time in my schedule for our metal shop. But my father is a machinist so that's helped me a lot as well.

Fission Chips (author)2014-11-19

This is really cool! I love kerf bending, and this is a really great Instructable. Thanks for sharing this!

JON-A-TRON (author)Fission Chips2014-11-19

Glad you like it! It's time consuming, but so worth the effort.

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Bio: I'm a full-time Designer at the Instructables Design Studio (best job ever). My background is in residential architecture, film set design, film animatronics, media ... More »
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