Eames Chair - Bent Plywood Question

[Steven McLeavin]

I've got a client who is dead-set on using bent plywood for the seat and backs of some bar stools. Having never bent any wood of any kind would there be any possible way to make bent laminations like this eames chair below without a vacuum press? The seat and back will be considerably smaller than whats in that picture, because it will be for a bar stool. And any suggestions on the material? Thanks!

http://theselvedgeyard.files.wordpress.com/2009/03/eames-chair-herman-miller.jpg

[mike holden]

Sure, you do NOT need a vacuum press for this.
Make a form to bend over, then glue the multiple plys over the form, laying down each separately, then clamp the dickens out of it. Would recommend using either Gougeon WEST system epoxy or System Three epoxies for the laminations.
Sailboats are made this way, as are iceboats.

However, you do know that these chairs are still being made? It might be cheaper to buy the chair than to build, once you factor in the cost of making all the metal components.

Pick up the book "Gougeon Brothers on Boat Construction" for more information.

On the other hand, this is one of the most comfortable chairs I have ever sat in. My boss had one in his office.

Mike

[David DeCristoforo]

The best way to make pieces like this is by vacuforming. You can make a two part mold but it will take a lot of pressure to pull the two halves together. A one piece mold will be problematic because it will be very difficult to get even clamping pressure.

[Jamie Buxton]

Okay, I'll give you a third opinion. You can do it other ways, but a vacuum press is by far the easiest. (You now have three responses, with three different answers.)

A key issue in stressed laminations like this is to have no voids --- no places where the lamination process failed to squeeze the laminates tight against each other. When voids occur, the plywood tends to flex and break. A vacuum press does this almost automatically. Mechanical clamping schemes, in my experience, sometimes fail at this.

When you get around to sourcing materials for this laminatation, look for stuff called bending plywood, or sometimes Italian Bending Poplar. It is 3-ply plywood built especially for this task. In most 3-ply plywood, the middle ply is much thicker than the face plies. This makes the plywood equally stiff in both directions. Bending plywood has a very thin middle ply. It is weirdly easy to bend in one direction, but very difficult in the other direction. My local dealers sell it in nominally 1/8" and 3/8" thicknesses.

[Doug Mason]

Jamie--I was at MacBeath in Berkeley last week and saw wiggle wood (1/8 and 3/8 diameter) and poplar (called bending ply - I think in 1/4 thickness). What is the difference between wiggle wood and the bending poplar? I'm guessing that the wiggle wood is for the forms and the poplar is for the veneer?

[Jamie Buxton]

Jamie--I was at MacBeath in Berkeley last week and saw wiggle wood (1/8 and 3/8 diameter) and poplar (called bending ply - I think in 1/4 thickness). What is the difference between wiggle wood and the bending poplar? I'm guessing that the wiggle wood is for the forms and the poplar is for the veneer?

Those terms, in my experience, are not used consistently. There's also another product which is like plywood or particle board with lots of kerfs cut in one face, and I've heard it called wigglewood.

I've bought 1/8 poplar bending plywood and 3/8 lauan bending plywood from MacBeath, and successfully applied veneer to each of them.

[David DeCristoforo]

There are three common types of material commonly called "bending ply". There is the 1/8" thick poplar ply which is very flexible mostly by virtue of it's thickness (or should I say "thin-ness") and the fact that it only has one core lamination. Then there is 1/4" and 3/8" thick bending ply. This material usually has three layers with the grain of the center one running "across" the two outside layers. The middle layer is very thin with most of the net thickness split between the two outside layers. Finally there are kerfed materials (Kerfkore, Econocore, etc.) which are plywood or MDF panels that are kerf cut to allow them to bend.

Any of these can be used to make curved panels using a variety of techniques. But to make a chair seat or similar bent component where there is no "armature" or other structure to hold the piece's shape, you are going to be dependent on glue lines. In any lamination that depends on glue lines for shape-holding, the more glue lines the better. Using 3/8" KerfKore or bending ply to make a 3/4" thick member will only give you one glue line. This will not be enough to hold the shape permanently. Using 1/8" ply will give you five glue lines. If you look at the Eames chair you will see that the formed pieces are made of 1/16" layers providing multiple glue lines, resulting in a very rigid lamination.

Regardless of which of the three materials you were to choose, I would still wonder how you would get even clamping pressure over the entire surface of something the size of a chair seat with no deforming of the materials unless you had a two part form or a vacuum press.

[Thomas S Stockton]

I personally would not use bending ply on this project. Unless you were planning on banding the edges somehow I think it would not look good. The originals were done using veneers for all the layers and I think the grain went in the same direction on all the layers. There is a lot of info on the Eames chair on the net that will help you understand some of the design details.
As David says you either need to make a two part form or use a vacuum bag. Check out the joewoodworker site you can get a lot of info from it and he also sells kits real cheap. You can also make a simple vacuum press for under $200 that would easily do what you need. Making a two part mold for something bar stool size would probably be fairly simple but a vacuum press is the easiest.
Thicker veneers are available from a variety of sources I would recommend certainlywood or Berkshire veneers.
Tom

[Jim McDonald]

"I personally would not use bending ply on this project. Unless you were planning on banding the edges somehow I think it would not look good."

The edges on mine are sanded and stained black...look great, but so does the chair...most comfortable, but being 40 yrs old, it's beginning to have some problems as far as the metal undercarriage goes. Have recovered the seat and foot stool and tried to rebuild the metal parts...really need to find original ones!

[Steven McLeavin]

Thanks for all the ideas! Would all 1/8 poplar ply be considered bending plywood? is this it (http://www.hobbylinc.com/htm/mid/mid5530.htm)? Because I don't plan or hope to do much bent ply stuff, i think i'll just try to do it with two forms. thanks again!

[Jamie Buxton]

...Would all 1/8 poplar ply be considered bending plywood?...

No. Re-read my description of what bending plywood is. The laminates are of different thickness than standard plywood.

[David DeCristoforo]

"Would all 1/8 poplar ply be considered bending plywood?"

Not at all. "Bending" ply gets it's flexibility by running most of the grain in one direction. "Standard" ply (regardless of thickness) will have layers (usually 5 or more) of equal thickness. Bending ply will typically have three layers. But instead of them being equal in thickness, the two outer layers will be very thick (in relation the the nominal thickness of the material) with their grain running in the same direction. The middle layer will be very thin and while the grain will run "across" the two outer layers (more to keep the material from being too weak and breaking) it will still be very flexible. The resulting lamination will be extremely flexible in one direction but still pretty rigid in the other. Some bending ply has only two layers, with the grain in both running the same direction. This material is intended to be permanently attached to some kind of structure and is very weak by itself even if multiple layers are bonded together.

PS Jamie already said most of that in a previous reply. I guess I'm just in a redundant mood tonight!

PPS Here's some links:
http://www.plywoodcompany.com/application/common/store/category.aspx?categoryid=20
http://www.curvolutions.com/BendingPoplar.html

[Steve Rozmiarek]

http://rozmiarek.smugmug.com/photos/463895378_hsJgZ-L.jpg (http://rozmiarek.smugmug.com/gallery/7096079_nhtXn#463895378_hsJgZ-A-LB)

I should have typed before I pasted the photo, but that is a photo of bending ply in a form, getting one of the layers of backer veneer applied, to go on the toddler bed below. In your project, I'd use the vacuum press, and a couple layers of 1/4" bending ply, with two backer veneers each side, followed by the show veneer.

On the piece in the photo, the next step was to pull the form out of the bag, and veneer the open face with backer veneer. In my case, where the bent lam is supported by the mortise on the rails, I only went with one backer layer, and it was very strong. Two layers of veneer might give a little more stiffness yet. Just to give you an idea of the strength of one layer of veneer on both sides of a sheet of bent 3/8" bending ply, I made a test run on this project, and the piece has been in my shop for 4 years now. I weigh 250 ish, and I can stand on the bow, and there is not much give. I've done this numerous times too, so if it was going to give, it has had the chance.

Do yourself a favor, and buy the vacuum press.



http://rozmiarek.smugmug.com/photos/463876519_DJVMc-L.jpg (http://rozmiarek.smugmug.com/gallery/7096079_nhtXn#463876519_DJVMc-A-LB)

[David DeCristoforo]

"Do yourself a favor, and buy the vacuum press."

+10! Or hit the site Thomas mentioned and get what you need to make one. BTW, that's an awesome looking bed, Steve....

[Steve Rozmiarek]

Thanks David, my daughter liked it too! Things like making bent lamination furniture unfortunatly seem to come about pretty rarely, so it was fun to take a break from building boxes, and do some curves.

[amir a. mughal]

Steve-- what was the form material you used, exactly? some kind of rigid foam, it looks like, eh? Help! I need to make a complicated sculpted form and that material looks ideal.

-amir

[Steve Rozmiarek]

Steve-- what was the form material you used, exactly? some kind of rigid foam, it looks like, eh? Help! I need to make a complicated sculpted form and that material looks ideal.

-amir

Amir, we emailed, so you know already, but I thought I'd post in case anyone else wanted to know too. It's just polystyrene insulation board from my local lumber yard. This form is made of the 3" stuff. I roughed it with a bandsaw, template shaped it on the shaper, then poly glue and doweled the sheets together. There was a bit of finish forming to do, and a rasp or coarse sandpaper work ok for that.