Making Curved Plywood

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Blog entry by DS posted 03-02-2012 07:05 PM 2979 reads 1 time favorited 12 comments Add to Favorites Watch

The Press:
I built my vacuum bag press from scratch last year and I was itching to try it out. A project came along that was just perfect for it. Curved plywood.

The pump is a pneumatic venturi that I got from joewoodworker dot com. It was the most expensive part of the build but not that expensive. It was surprisingly efficient at drawing a vacuum.
As you can see, in an Arizona summer it drew 24.5 inches of Mercury.

Subsequent builds I acheived 27 to 28 inches of mercury, which is pretty good, if you’re taking notes.
Eventually I will put an automatic valve on it, but I found if I hang out in the area a couple hours while it is in the press and take note of the pressure guage I can manually recharge every few minutes and not have an issue.

For the bags, I found I can buy the same vinyl in rolls at the fabric store (10mill thick instead of 30mil of the commercial ones) and buy heavy duty double sided tape at HD and make “semi-disposable” bags for real cheap. It worked out great. Besides, no one makes the 10 foot bag that I would need for this project.

The Build:
The first step in the actual plywood making was to create my form. For this I made a type of torsion box from 4’X10 PB which I laminated with 3/8” wiggle wood. No additional layers were needed.
My daughters paid a visit just as I was gluing up for the top and they we eager to lend a hand.

Before running the full laminations, a test was in order. I needed to be sure this system worked before committing expensive plys and veneers to this. Besides, I need to create color samples too, so it fit the bill perfectly.
The layers from back to front looked like this; 20 mil Polybak Liner backing, 1/8” MDF, 3/8” 3-ply wiggle wood, 1/8” MDF, 20 mil Red Oak veneer face. If you look closely you can see the plys for the finished panels underneath the form biding thier time.

I used standard PVA adhesive for the plys and chose NOT to put the form in the bag. At this size, the bag would crush the form anyway, so I used the off-fall from the form ribs as cauls on top of the bag. It held its shape without any coersion at all. Nice.

At the time of this project, I was cramped into 1/2 of a 2 car garage. It always looked cluttered, but when this took most of the space, it got crazy for a few days.

This was to be part of a rostrum in a church, actually a Jewish Tempe. Someone attempted to do this themselves by bending 1/4” ply over a frame and failed. Too many bumps along the way, finishing issues and the like. Thicker plywood would make for a really clean and quality look and I got the nod to finish the job.

The Layup:
Unfortunately I don’t have pics of the layups in the press. I had my hands full spreading glue under a timer. Even with a helper this was an intense process. The panels are just over 9 feet long and there were a couple inner seams in the substrate. I staggered the seams throughout the layers and prejoined these whenever possible before the final layup.

Here is a look of the finished panels just before delivery.

The Finished Installation:

I think these speak for themselves.

Another satisfied client.

Thanks for following along.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

12 comments so far

View patron's profile


13610 posts in 3391 days

#1 posted 03-02-2012 07:13 PM

these came out beautifully

nice tip about the plastic
at the fabric store

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

View SPalm's profile


5320 posts in 3932 days

#2 posted 03-02-2012 07:27 PM

You got skills.

Interesting layer stack of mdf-wiggle-mdf. I guess the mdf was a smoother surface for the veneer?

Thanks for the inspiration,

-- -- I'm no rocket surgeon

View Joe Lyddon's profile

Joe Lyddon

10146 posts in 4102 days

#3 posted 03-02-2012 07:48 PM

COOL Job… COOL installation!

You had no room for being off much on that curve did you? Did you have any spring-back at all?

How did you record that wall curve so you could use it to prepare your vacuum frame?

You mentioned that you made the vacuum bag press from scratch… did you post it?
If not, it would be nice to see how you did it.

Oh, I think you wrapped those panels before you transported them… and you just propped them up in your truck for the pictures… right?

-- Have Fun! Joe Lyddon - Alta Loma, CA USA - Home: ... My Small Gallery:"

View DS's profile


2928 posts in 2470 days

#4 posted 03-02-2012 08:15 PM

@Steve: That is the typical “Classic Core” construction that you can buy commercially. (With exception of symetrical plys instead of wiggle wood plys) The resin impregnated backer and the front veneer really locked the radius. It was a very strong peice when it was done.

No spring back, as each layer had little or no tension there. The wiggle wood has a single cross grain ply in the center that is fairly thin. Once it was cured you couldn’t bend this if you wanted too. It was set.

Figuring curves is fairly straight forward. Measure the chord of your curve (A). (End to end in a straight line.) Mark off a point somewhere close to center and note that. (B) Measure from that point on the chord to the wall©. This gives you a 3-point curve which can be plotted in CAD fairly easily.

And yes, they were propped up for the photo. Though, for transportation, it was a beautiful day and I brought them together and strapped them in standing up. You might notice that I recycled the cauls to help stabilize the panels for delivery. That allowed them to stand up well enough.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View DS's profile


2928 posts in 2470 days

#5 posted 03-02-2012 08:27 PM

@Joe, regarding the bag. I haven’t posted it, nor do I have any good photos of it.
I had previously done a dining table with a leaf in Sapele where I had a reverse diamond matched top. What a PIA it was to lift all that into the bag while under a time crunch with the adhesive.

I found that I could set the bag on the form first and pre-tape the lower portion before building my layers. When it was time to close it up, I simply folded the bag over the top and pulled the self adhesive tape backer off from between the layers as I pressed the bag shut. To reuse the bag for the second panel, I was able to cut off the first tape, making the bag a little smaller and then start over with new tape for the second panel.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View DS's profile


2928 posts in 2470 days

#6 posted 03-02-2012 10:13 PM

@Joe: I just reread your last post and realized you asked about the press and not the bag.

No, I haven’t posted the press. My verison is greatly simplified from the joewoodworker version and can be made for about half the cost. I always intended to upgrade it, but haven’t had the call for it yet. I may do a diagram of it and post it in a blog all its own. Good idea. (In my free time of course – heheh)

I tend to let my jobs pay for upgrades to such things as I go. It’s not a bad way to accumilate tools.
The Bar I just finished just paid for my new table saw, for example. There wouldn’t be a budget for it otherwise.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View Dave's profile


11429 posts in 2890 days

#7 posted 03-02-2012 10:43 PM

A professional job you have done. I am sure you client is happy. The blog was detailed and well written. Nice

-- Superdav "No matter where you go - there you are."

View stefang's profile


15881 posts in 3384 days

#8 posted 03-03-2012 10:25 AM

I’m very impressed with the result, but I have to admit that most of this was totally beyond me.

-- Mike, an American living in Norway.

View Roger's profile


20929 posts in 2854 days

#9 posted 03-03-2012 12:49 PM

wow! very nicely done. thnx for the details

-- Roger from KY. Work/Play/Travel Safe. Keep your dust collector fed.

View Lee A. Jesberger's profile

Lee A. Jesberger

6860 posts in 4029 days

#10 posted 03-03-2012 12:59 PM

Great job.

You mention no one makes bags that size.

For the record, you know you can get custom sizes of commercial bags. hey are expensive though.


-- by Lee A. Jesberger

View shipwright's profile


8000 posts in 2848 days

#11 posted 03-03-2012 02:43 PM

You can also make vinyl bags with pool repair glue, very easy.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees.

View DS's profile


2928 posts in 2470 days

#12 posted 03-05-2012 03:25 PM

@Paul: My first experiments with bag making I used a vinyl adhesive that was available on the site where I got the venturi. This worked okay, but was time consuming. Clamping the edges and closing leaks was a tedius process too.

I found the tape worked as well as, or even better than, the glue and I could quickly reconfigure the bag. The roll vinyl from the fabric store was only a few dollars per yard and the custom bags were fairly inexpensive.

@Lee: Commercial bags of the size I would’ve needed would run $300 or so. The ones I made cost less than $30.
It’s hard to beat that.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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