Introduction: Benches and Tables Built As Stressed Skin Panels

Picture of Benches and Tables Built As Stressed Skin Panels

The 5-foot bench panel pictured above, with over a thousand pounds of gravel on it, uses 1/4 as much tree to create, yet has the comparable strength of a 2 inch thick solid wood slab. The panel itself weighs less than12lb and is a structural beast!

The stressed skin panel is an incredibly efficient engineered scheme, in which the structural material is only placed where it can do the most good.

I have made benches, tables, a motor home interior, and a large building, from stressed skin panels.

To date, I have used plywood, door skin, frp, osb, and reinforced concrete for the skin. And, and for the innards, I've used eps foam, ribs cut from plywood, and steel open web trusses, all with good result.

In this instructable I will discuss in detail, how I construct the panels for the upholstered benches that we sell, and also some table panels that I am working on as well. It's really about the panels themselves and not so much about general shop skills or the upholstery etc, I will include a video on the making of the legs.

I think these panels are well suited for furniture construction. I'm going to make all sorts of stuff from them.

Step 1: Bench and Table Panel Sandwiches

Picture of Bench and Table Panel Sandwiches

A stressed skin panel consists of a structural skin and a lightweight rigid core, like a surf board, hollow core door, or airplane wing.

I make the bench panels with 1/4" baltic birch plywood, 2lb density eps foam and wood glue, I use Titebond 2 or 3.

We make the benches in lengths from 3-feet to 8-feet. I use the same 1/4" ply for each but a different thickness foam, this gives me a thicker stronger panel for each progressive bench length, just by adding more foam.

I use a notched trowel, which is fast and that's important as you need to get the glue spread and the panel assembled before the glue dries.

You can pile a bunch of flat heavy stuff on top in order to clamp it while the glue dries, or make some sort of clamping fixture, my latest is 2-feet x 8-feet, made of 6-inch thick ssp's and utilizes pipe clamps.

I have also built table tops of similar construction but with a 1" deep solid perimeter of the same birch plywood. This gives the table a very robust edge of very nice looking plywood edge grain.

I have also used strips of the same 1/4" plywood used for the skin, as ribs glued in place instead of the foam core, to excellent effect. This eliminates the expense of the foam and makes use of what would other wise be scrap pieces of wood, and requires a small fraction of the wood glue compared to the foam version. Though until I figure some kind of jig, it is a lot more time and labor intensive than the foam version.

As to proportions, you can certainly make very useful panels with less wood than described above. I am not aiming for the lightest, most efficient panels here, I want very stout tough pieces of furniture, I just don't want to wastefully fill the center of the beam with structural material where it is of no structural value. the 4x5' dining table tops weigh over 40lb, which is about 80lb less than they would weigh if made of solid plywood.

Step 2: Cut It Into Any Shape You Want

Picture of Cut It Into Any Shape You Want

These panels cut quite well with all manner of woodworking tools. I cut the final shape with a router, I'm not going to teach you how to router, you'd probably just learn bad habits.

I will say that I really like this urethane router guide, you just bend it to the shape you want, and screw it into place, I use a print from a cad drawing.

I cut a template from a piece of plywood. I then use that template to cut the benches of a given shape and length. The template is also a drill pattern for the 12 leg mounting points. If it's a one off bench then I use that nifty urethane guide directly on the panel.

The longest thickest benches are too thick for the tallest router bits I have found so far, so I have to cut from one side then move the template to the other side and then cut that side. I do this by using the holes cut for the legs to register the template from either side.

We have two shapes that we make and sell, we call them Blood Cell and Dog bone. Use your imagination and make any shape/length you want.

As for the table panels, the shape is determined by the perimeter frame of solid plywood, so I just trim the skins down to the frame with a router and pattern bit or with a circular saw.

Step 3: Hardware

Picture of Hardware

I mulled over the hardware question for years before I came up with the following solution and could finally proceed with the benches.

I ultimately came up with something that, uses off the shelf components, allows me freedom of placement, meaning I can place the hardware anywhere I want after the panel is already made, and leaves me with a 1/4-20 steel female machine thread.

I drill 5/16" holes through the panel. I hammer a wide flange t-nut into each of these from the top side, and into each of these from the bottom side, I install a threaded stud and weld nut, previously welded together just so. I glue these in place and tighten them with a screw and screw driver until I can feel the panel start to distort inward around the weld nut, then I remove the screw and I am left with a 1/2" deep blind threaded steel female thread, which is of course wonderful.

This of course only works if you can live with these t-nuts exposed on the top side of the panel, as is the case here with the benches where they will be hidden underneath the upholstery.

This is not necessarily so good for a table and it's exposed top side, so I've been doing those with a solid wood insert, and then I use a threaded insert or you can simply screw directly into the wood.

Step 4: Upholstery

Picture of Upholstery

My better half is in charge of the upholstery, sorry I don't have process pictures here, but again this instructable is more about the panels.

I can tell you that the upholstery utilizes 1" hi density hi resiliency polyurethane upholstery foam, polyester batting and rugged upholstery fabric that we usually buy as remnants.

They are boxed without welting and stapled using standard techniques.

We use the thin but firm foam because we want a streamlined not so thick look. I think it's just right even for my skinny butt.

Step 5: What About Those Legs

Of course we use our own design spiral cone legs that we make and sell, but you can use or make anything you like with these panels.

This instructable isn't so much about the legs, but we do have this video that shows how I make the legs, so I'll include it here.

You can see more of the legs and benches at our website, SpiralConeLegs.com

Step 6: More Photos and Some Proselytism

Picture of More Photos and Some Proselytism

When I first learned of stressed skin panels, I was immediately struck by their lack of broader use in our built environment.

We live in a world of flat panels, a plurality of which would be better served if built as stressed skin panels. The walls of our homes for instance, would be of vastly higher quality in every way, if they were made in such a manner. The stressed skin panel is a marvel of efficiency , and should be all over our manufactured landscape!

Comments

obillo (author)2017-12-21

This is just the ticket for owner-built housing. In 1975. my neighbor Dave Surbeck designed a house of modular panels to be constructed on his property on Martha's Vineyard. The basic module was a 4x8 ply panel with 2x4 stringers between. The stringers were all the same, for the idea was to make the panels into giant tongue-and-groove units. So, on one long side of the panel, the first 2x4 would be nailed/glued 2" in the the edge (that is, the thickness of a 2x4). That constituted the groove. On the other side, two 2x4s were nailed/glued together and laid down with one of those 2x4s sticking out from the edge: thus we had a tongue on that side. We also laid 3 parallel 2x4s between them, packed in some insulation and spread glue by the long ton. Then the top 4x8 was laid on and nailed down in a frenzy of hammering. We used long cement-coated nails called 'sinkers' locally. Every night after work and before supper I'd go to Dave's and we'd bash panels together in his cellar. We got to be pretty good at it, eventually getting to three panels and hour between just the two of us (other friends gave Dave a wide berth--he always had a hammer to offer anyone who'd use it). The next summer we loaded the panels and some huge beams and columns into a rented truck and drove them to the Vineyard from eastern Pa. We had the house assembled in about three days, and after that there was just interior finish work to be done. Here's what the panels looked like in cross-section, if you're willing to think of the Xx as 2x4s:

------------------------------------

XX X X X

-------------------------------------

I'm sorry about the disgraceful crudeness of the above. Maybe it will be clearer if imagine away the space between the tops and bottoms of the Xs.

Anyway the result was a delightful summer house that still serves the Surbecks 40 years later. It cost very little and was an easy build. I tried to get Dave to publish and sell plans, but he couldn't be bothered. At any rate, all you really need to know is the 'secret' of the tongue-and-groove panels.

LanceBuilt (author)obillo2017-12-26

Thanks,

You
friends project reminds of our own building, in that I've been Tom
Sawyering my friends and neighbors into helping me get the thing built,
without whose help I would have met with failure long ago.

LanceBuilt (author)obillo2017-12-21

Fantastic!

dpswords (author)2017-12-25

hi

awesome instructable dude.

Im looking at a bed platform for a tiny house and was going to use this build instructable, any thoughts? thank you thank you thankyou great info

LanceBuilt (author)dpswords2017-12-26

Thanks,

I built our bed this way more than a year ago. The main obstacle is that, other than a twin, beds tend to be larger than sheets of plywood. On ours, a queen, I used 1/8" ply and built it up staggering the seams, kind of making my own plywood so to speak.

I later thought it would be easier to just seam the 1/4" ply with a single strip of the same that would be glued over both pieces and placed on the inside. And then just have the foam skinnier at that place. I figure I'd place the seam not at the center where it needs to be the strongest and also probably not at the same place on either side.

If you are upholstering the bed you can just leave the foam exposed at the edge and cover it with the upholstery like we did, or have a solid wood edge like the table panels in the instructable.

Good luck and let me know if you need some legs for it.

Thoreaven (author)2017-12-24

nice instructable and I love the legs. If you like stressed skin panels, check out foam core hulls.

LanceBuilt (author)Thoreaven2017-12-25

Thanks

lorenkinzel (author)2017-12-23

The walls of our homes, with drywall inside & ply or OSB outside ARE stressed skin panels with 2x4s or 2x6s as ribs.

For the sake of speed over quality we use nails instead of glue.

Watching demolition of walls with plywood on 1 side, it is amazing what it takes to break them.

Ralphxyz (author)2017-12-21

Why are they called "Stressed Skin Panels"??

Where does the stress com from?

Thanks for the instructable, hopefully I will eventually get around to using it.

Ralph

LanceBuilt (author)Ralphxyz2017-12-21

Image result for compression and tension in a beamfrom resistance to the load, in a beam the work is all being done at the bottom and the top, the top being in compression and the bottom being in tension. As you move toward the center the ability to help structurally diminishes greatly. In a stressed skin panel the structural material, the skin, is placed where it has the most leverage to do the work, at the surface, the thicker the panel, the more leverage it has.

Ralphxyz (author)LanceBuilt2017-12-21

Thanks interesting

Ralph

markstutzman (author)2017-12-21

Pretty cool. Are you using standard yellow PVA wood glue to glue up the plywood-EPS sandwiches?

JamesB670 (author)markstutzman2017-12-21

Am also interested in what has been found to work well in terms of gluing to EPS...(?)

pgs070947 (author)JamesB6702017-12-21

EPS is hydrophobic so any water-based adhesive is going to struggle.

Having said that, a prime with PVA, well scrubbed in, will take a solvent-free adhesive like Gripfill Solvent Free.

One adhesive that seems to work on just about anything is (in UK at least) is one by Geocel/Dow Corning called "The Works" or Sika Sikaflex EBT

I haven't found anything that this doesn't stick, works under water and I've used it for a whole string of things, including:-

Bonding work surfaces together (Mason's mitre joint)

Fixing PVC cladding to exterior woodwork

Repairing a live water leak on a tank by mixing it with glass fibre mat

Fixing rigid PUR insulation panels

Fixing fittings in shower cubicles (no tile drilling)

If you use it on wood joints, the wood will break before the adhesive, and of course, totally waterproof.

charlessenf-gm (author)pgs0709472017-12-21

"seems to work on just about anything is (in UK at least)"

Well then, let's not bring those items to the US! ;)

$55/tube! https://www.amazon.com/s/ref=nb_sb_noss?url=search...

pgs070947 (author)charlessenf-gm2017-12-21

I'm sorry to hear that you are being ripped off, but maybe you should ask Dow Corning why a cartridge of adhesive that retails at less than £10 (and that's pricey) in the UK and so much in the States - after all Dow was originally a US company. The Sika brand is even cheaper at £6 a cartridge.

I would suggest you do a bit more shopping around instead of relying on Amazon. Or maybe ask Mr Trump what he can do about it.

LanceBuilt (author)JamesB6702017-12-21

I use titebond 2 wood glue, I'm sure you can use lots of adhesives though there are some that will melt the foam. I've also used gorilla glue when I was gluing to some frp that wood glue wouldn't stick to

LanceBuilt (author)markstutzman2017-12-21

I use titebond 2 wood glue, I'm sure you can use lots of adhesives
though there are some that will melt the foam. I've also used gorilla
glue when I was gluing to some frp that wood glue wouldn't stick to

charlessenf-gm (author)2017-12-21

Very impressive and creative use of the construction techniques. Kudos to the upholsterer as well!

"I have also used strips of the same 1/4" plywood used for the skin, as ribs glued in place"

I built a 30-inch x 78-inch x 1.25-inch shelf years ago using the ribs. However, I created a lattice with the ribs (notching appropriately at the intersections) after a design I saw called Torsion Box construction.

It was extremely light weight - I used .125-inch philippine mahogany 'door skins' over ribs cut from ordinary two by fours and spaced (as I recall) about 4-inches on center in each direction with the edges of thicker ribs notched appropriately to fit (and glue) the ends of the internal ribs.

I appreciate the flexible router guide - never heard of it before! If you have not listed a source - please add it.

Looked at your legs (blushing).

Noticing the Ball Feet, I wondered if there was a Ball Caster you could make or purchase to allow for rolling tables! If the rolling ball could be 'captured' in the partial ball fixed to the bottom of the leg such that the captured ball might move freely . . . hmmm

I had a customer who asked about that and I considered trying this with ball transfers like they use for conveyor systems. But never tried it.

Excellent, yes having the the ribs cross one another, running in two directions is great, I figured I could get away without doing that because my thick solid wood edge frame would keep the thing stable.

The router guide is from cmt,

https://www.amazon.com/gp/product/B00FATEUI4/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

carl5blum (author)2017-12-21

A-Liner Pop-up Campers use stress panels too. Thinner plywood inside (4mm) and aluminum or fiberglass outside. I still have the cut out if you need some. Carl.

charlessenf-gm (author)carl5blum2017-12-21

"I still have the cut out"

Well, then, fill the edge and make an aluminum-skinned occasionaal table!

LanceBuilt (author)carl5blum2017-12-21

very cool

AngryGazebo (author)2017-12-20

They actually have been using this technique for building houses since the 30s but didn't become very popular till the 70s. They are called SIPs (Structural Insulated Panels)

http://www.sips.org/about/what-are-sips

LanceBuilt (author)AngryGazebo2017-12-21

Yes indeed those are great, I've also seen a product that was foam panels with a layer of steel reinforcement on either side. You'd assemble the panels, wire them to one another and spray either side with concrete, pretty slick. I think they were called tri-d panels or something like that.

HoffS (author)2017-12-21

One concern I would have with this approach is flammability. Having said that, I have an Aliner that uses this technique.

LanceBuilt (author)HoffS2017-12-21

Yes as 700 + homes just went up in flames in my home town of ventura, this is on my mind. Concrete works great as the structural skin for such panels, and in addition to being non flammable you have the benefit of all that thermal mass to help keep the interior comfortable.

my5377 (author)2017-12-21

How can I find where you sell these?

LanceBuilt (author)my53772017-12-21

http://spiralconelegs.com/

KimberleyH (author)2017-12-21

I really love the bench/table legs, more interesting than the hairpin tables legs. Interesting tutorial.

LanceBuilt (author)KimberleyH2017-12-21

Thanks, check out our website,

http://spiralconelegs.com/

obillo (author)2017-12-21

Me again. My rough drawing was bad enough but Ibles' word processor made it worse. Sorry, but you'll just have to work it out from my description. Or maybe some Ibler who can draw will help out.

obillo (author)2017-12-21

Sorry--in the above I mean the stringer were NOT all the same, asone of them consisted of 2 2x4s nailed together and the other were singles.

Lagather (author)2017-12-19

Very cool use of materials. Did you buy or make the urethane router guide? If buy, then where did you find it?

LanceBuilt (author)Lagather2017-12-20

Thanks, It's sold by cmt who make router bits.

https://www.amazon.com/gp/product/B00FATEUI4/ref=o...

They also make a shorter one for about half the money.

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Bio: I have been taking things apart and putting them back together since childhood. It has long been my dream and effort to make my own ... More »
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