Creating compound curves with plywood?

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Forum topic by Underdog posted 05-20-2013 08:18 PM 14137 views 0 times favorited 18 replies Add to Favorites Watch
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1223 posts in 2232 days

05-20-2013 08:18 PM

How would you create a compound curve in plywood?

Say for this kind of hood?

Granted, the one shown is probably copper, but I’d like to make one in wood, and wonder how you can get that compound curve with plywood?

Any ideas how one would go about creating this?

-- Jim, Georgia, USA

18 replies so far

View shipwright's profile


8162 posts in 2994 days

#1 posted 05-20-2013 08:41 PM

You can’t make truly compound curves with flat sheet stock. That said you can torture thin plywood a bit and these are quite easy curves so you may be able to make a form and laminate a couple of layers of 1/8” or something like that.
The best way would be to “cold mold” it from smaller pieces. I’ve built boats with serious compound curves that way. There’s a simple explanation of the process in this blog, Although the piece being made there is not a compound curve the same principles apply, just the individual pieces may have curved or non-parallel sides.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View huff's profile


2828 posts in 3481 days

#2 posted 05-20-2013 08:52 PM


From the picture it looks like even that hood was done in 3 panels.

You can buy bendable 3/8” plywood and laminate a couple layers together to get and hold your shape.

You would have to build a form to fit the plywood to while gluing and clamping the layers. If you check out my avator you will see a project I did using the bendable plywood. I veneered it after I had the carcass built. Face frame, drawers and drawer fronts where from solid wood and the entire case and dividers where done with the bendable.

You can google it to find a supplier.

Good luck.

-- John @

View PurpLev's profile


8547 posts in 3845 days

#3 posted 05-20-2013 08:57 PM

actually – yes you can create these types of curves with flat sheet stock but not “as-is”

if you take sheet stock (plywood) and notch the back you can bend it to quite small radii curves. the closer the notches, the tighter the curve can be made

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View Underdog's profile


1223 posts in 2232 days

#4 posted 05-20-2013 09:02 PM

I have successfully used the kerfing method to make “simple” concave and convex shaped hoods.

What I’m talking about, compound curves, shown in the link above, is a whole different animal…

-- Jim, Georgia, USA

View madts's profile


1873 posts in 2536 days

#5 posted 05-20-2013 09:03 PM

Gougon Brothers have a book out about tortured plywood. You can do quite unbelieveable things to that stuff.

-- Thor and Odin are still the greatest of Gods.

View DrDirt's profile


4509 posts in 3938 days

#6 posted 05-20-2013 09:04 PM

I think the three panels they show would be simple in say 3/16 ply. Cut a groove into the back of the face panel, then pulling the panel square at the top will work fine.

Need to just include some formers beneath, and you will then have a hollow form, with a contoured top, and flat inside. The curves are gentle enough that thin ply will follow it.

You can always laminate a panel in a vacuum bag.
We made longboard skateboards that are cambered (arched) front to back but also dished from wheel to wheel. Those were done with 3 peices of 3ply birch ply (1/8) with about a 1/16th veneer skin top and bottom with the pattern in it.

-- “The two most important days in your life are the day you are born and the day you find out why.” Mark Twain

View REO's profile


929 posts in 2270 days

#7 posted 05-20-2013 09:06 PM

bending ply is made for simple curves in order to make a compound curve the material has to either stretch or shrink. The curve you show is not that drastic that the right veneers may form without splicing. steaming and vac forming each layer before final glup up may get you what you want.

View Buckethead's profile


3194 posts in 2065 days

#8 posted 05-20-2013 09:08 PM

Shipwright seems to have the best answer. I could offer suggestions on modifying the design to mimic the overall appearance, but using a single piece of plywood seems like a tall order.

Alternately, you could use strips of wood which bend around a curved frame, which could form the eyebrow, but that would require bondo or such to finish the job. Is it to be painted?

-- Support woodworking hand models. Buy me a sawstop.

View Loren's profile


10477 posts in 3844 days

#9 posted 05-20-2013 09:34 PM

You can do it by making a form and cutting thin plywood
or veneer into strips, building up layers with voids
on the form. Clinching nails could be handy for this -
I use them for making sandals but nails are also
clinched in bent shaker boxes and other traditional
wood craft items.

Finally you have the shape built up and then you smooth
it out with wood fillers and carefully veneer it with tapered
veneer flitches.

You could also just faux paint it to look like wood.

Lotsa work for a one-off.

View Buckethead's profile


3194 posts in 2065 days

#10 posted 05-20-2013 09:37 PM

If you’ll pardon the rudimentary attempt at drafting, you can get a (bendable) sheet of plywood to bend in this fashion. The top radius being uniform, and the lower edge using three radii. Two opposing (concave) which forms a steeper curve in the convex center.

-- Support woodworking hand models. Buy me a sawstop.

View dartzt's profile


54 posts in 2278 days

#11 posted 05-20-2013 09:59 PM

It seems I remember a product called Bendy Board? plywood type material .. yep just googled it…. it’s not cheap but looks like it may work

-- Darren A. - Bosque County, Texas "Nothing great was ever achieved without enthusiasm" - Ralph Waldo Emerson

View joeyinsouthaustin's profile


1294 posts in 2269 days

#12 posted 05-20-2013 10:00 PM

Buckethead and shipright are booth on track, IMO. I have bent a curves close to this with two layers of 3/8 ply. as well as conical ones. I used a form that allowed for vertical cauls along the whole form, with the ones a long the compound shaped more severely. You have to work from the right point out, and you will hear a lot of cracking as you clamp past certain points.

-- Who is John Galt?

View Loren's profile


10477 posts in 3844 days

#13 posted 05-20-2013 11:09 PM

View Tony_S's profile


955 posts in 3279 days

#14 posted 05-20-2013 11:22 PM

It’s definitely not wood. Doesn’t look like copper either.

Can it be done with flat sheet stock, one piece(several layers) for each of 3 panels? Rubberply or otherwise? Exactly as seen?
Never say never, but an educated guess would be no, not exactly as seen. The sheet goods would more than likely split(almost guaranteed).

Pieced together and filled,(bondo is my choice) sanded to a smooth, even, transitional plane and then veneered in pieces as Loren mentioned would be my ‘how to’.
The good thing about rubber ply in this instance, is it’s typically made of Luan on both faces and sands quite easily.
Would your project be for an actual range hood? If so, the combinations of pure dry heat one day vs. possible large amounts of steam the next day would be a major concern as well.

Your in for a $*@! load of work.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View Underdog's profile


1223 posts in 2232 days

#15 posted 05-22-2013 05:12 PM

Well, I’ve been doing CAD drawing all morning. Looks like I’ll be using 1/4 ply in strips with a sort of cold molding process.

I have the advantage that the seams will be covered by trim strips, so I can cheat a little if they don’t come together exactly.

Here’s the original picture the customer gave me:

I’ll be replicating this minus that tall arch for the window. The arch will be much more shallow, so that makes it easier.

Thanks for all the great input!

-- Jim, Georgia, USA

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