Typically bent plywood is built bent. That is each ply is glued in the mold. If you can find real veneers at a hardwood store, you would save yourself some serious pain-in-the-ass type work.

As far as what you are tryng with exisiting plywood, steam seams like it may work. But watch out for that formaldahyde and urea filled glue.

Hey Pixelwhore! We need your expertise.

You should glue up the ply's on the mold. Steaming the plywood and then clamping it won't really work. The plywood will just creap back to straightish over time. 8' is a pretty big radius, so steaming probably won't be neccessary at all. If you can't find pre cut veneers, you can resaw a hardwood plank down with a large blade bandsaw. 1/8th is about the right thickness. Also for your dimensions i'm guessing it won't be neccessary to alternate grain direction. Also don't use wood glue, it will creep and delaminate over time. Use an epoxy resin like WEST system (thats what it was invented for) or a laminating glue like Resourcenal (sp?). Make sure to apply even pressure along the entire lenth to avoid pockets (partially mitigated by the spanning ability of epoxy). mm k.

ok, i dont know if this will be good for you but here it goes

run the strip through the table saw making 1/8" cuts (alternating between cut, then 1/8 strip then cut then strip, leaving a bit of material to act as a veneer so if its 3/4" plywood set the blade to about 21/32", it should be very bendable now that you have removed the material but this will probably take a couple mockups,

when youre done, glue all the empty slots, jig it up and well let it dry

should be good

or glue the top of the "veneer" left, and apply another thin veneer 1/32-1/16" over it then jig it up and it will be pretty clean

in my head this works but you just gotta try it a couple of ways

a little kink though i just thought of, the thickness of the plywood combined with the size of the material removed vertically and horizontally will sort of dictate the radius, its tricky

seen it done with round cabinet edges with strips of wood glued to a veneer....which is another way to do it additive versus subtractive

There is a product Custom Cabinet buiders use which is a plywood called "Wacky Wood" you can form it into most anything you want.

Ross..your plywood piece is very long 8 feet .

u havent mentioned how thick it is..

make small nicks across the 4" side of the piece..1" centre-to-centre going about halfway down the thickness of the piece.

along the eventual inner circumference of the circle
(e.g if your hand is the face of the plywood. and your eventual circle will be like your thumb touching the tips of all your fingers, then the nicks should be made on ur palm.)

else no amount of steaming will help, the plywood will break after some time.

Some of the ideas mentioned are good ideas if only one side of your strip will be visible, and you will be capping the top and bottom.
If you are looking for all surfaces to have a finished appearance the best way is to build a mold and use 1/8” veneer plywood strip and created your own lamination. Take a look at this book, there are many methods of creating a radius with plywood.

The buildup method works well.

I found some 1/8" cypress and I just made these in my shop for a house I am finishing:




They are to be stained a color and are going outside.

mAKE aRCHITECTURE,
nice work!
i love the mateiral, i amworking on some furniture pieces my self,
i need to learnd how you guys do it, posting your own picts, that very cool. I wanna show my curves now!

thanks for all the responses. I should have specified a few more things before

I would actually (potentially) be needing to make hundreds of the 4" x 8' strips, on a pretty limited budget so price and speed of work would both be issues.

as far as thickness, roughly 1/2" to 3/4" but this isn't crucial. thinner would actually be more translucent and might let a little light through on a sunny day.

the project is for an outdoor installation so the ply will be exposed to the elements, but only for about 6 months. both sides will be visible as well, but I'm not totally opposed to seeing scoring on the back side.
maybe, maybe not.

I did some searching during lunch and came across a material called "wiggle wood" / bending stock. It sounds like plywood strips with the grains all oriented the same way so that it is easier to shape. it could be similar to the wacky wood snooker mentioned.

again, thanks for all the suggestions. any more advice would be welcome as well.

i have used bender board. it is 1/8" thick and has a veneer on one side. i used a vacuum press and laminated 3 pieces together. i was ale to get about a 3" radius without splitting the veneer. i used three layers and have the veneer exposed on both sides. once finished it looks like plywood and the stuff is cheap - well cheaper than laminating layers of veneer together.

ross, I think you should think about another material. Wood isnt going to be cheap if you want it to last that long, and translucent? you are talking really thin then.

Rolled mtl (steel or aluminum) could be allowed to rust or be painted or even acrylic can be bent really easily...might turn out better in the long run.
If a bit thicker shape is feasible you can cut shapes out of foam with a hotwire and fiberglass them.
Bender board doesnt hold up very well to weather, nor does most ply-wood even when it is exterior grade.

scoring would be the way to go, if you cut angled notches crosswise you should be able to glue them together to form a nice curve. seal it with polyurethane and you have a weatherproof option.
you may also make a jig and laminate a few pieces of thinner wood together. this would require some experimentation if the curve needed to be precise but after it was set you could fabricate the pieces continuously

if you really want plywood:

order up some 1/8" wiggle ply, specify that it should make a 4' column (grain runs the short way). make your form and caul with about a 7' 6" radius to allow for springback. use waterproof glue and 3-4 layers. if you work quickly you should be able to make up several sets, stack them in the mold, and clamp the whole thing up. If you're using yellow glue (titebond II) wait at least 40 min before taking off the clamps.

I've used a similar process for larger curved panels, and expect it would work OK for you, and should be pretty quick once you get the process down. Honestly, though, I don't recommend it. the curved pieces will tend to warp, and won't remain nice flat arches without some sort of bracing. Also, you'll need to seal them up well or they won't retain their shape in the weather.

The various kerf-removal methods work well for giving flexiblity to pieces that will be held in curve, but will be difficult to stiffen.

I'll second the recommendation for bent acrylic. weatherproof, bends easily enough, and not much more expensive than all that plywood. I've seen homemade acrylic bending jigs that use a small heating element and work pretty well.

Good luck