bending plywood

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srinath

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#1
I have this crazy idea to make speaker cabinets with bent plywood walls. It doesn't have to be crazy bent, just a little is fine.
What would happen if I tool a 4 ft long 24" wide 3/4" piece of plywood, sat it on 4' long, 4" posts and put a towel in the middle and poured boiling hot water on it for 3-4 hours, and then put a big heavy steel 4" pipe in the middle lengthwise while continuing to pour hot water.
Basically heat and water to soften it and then weight to bend it gently into where it will be comfortable.
And It will give me a 48" long, 24" wide bent piece of plywood where the middle is 4" lower than the edges. It wont be a proper circle or much of anything curve (well it will be a catenary wont it ??? )

Cool.
Srinath.
 
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#2
why not create a form and use several plies of veneer?
i think steam, a steam cabinet and maybe a week's time might work for shaping plywood but i'm not the most skilled woodworker around. is plywood not cross laminated to prevent it from bending?
 
#3
turk 182 said:
why not create a form and use several plies of veneer?
i think steam, a steam cabinet and maybe a week's time might work for shaping plywood but i'm not the most skilled woodworker around. is plywood not cross laminated to prevent it from bending?
Click to expand...

Laminate several sheets to form curved plywood...yes

Bend plywood...not very much

Or make saw cuts most of the way through on the inside of the part you want to curve and fill with glue when curved...there is a name for this technique...escapes me right now.
 
#4
DUG said:
Laminate several sheets to form curved plywood...yes

Bend plywood...not very much

Or make saw cuts most of the way through on the inside of the part you want to curve and fill with glue when curved...there is a name for this technique...escapes me right now.
Click to expand...
If the radius is considerable, I would consider wiggleboard instead of plywood. Or use several layers glued together under pressure. This will allow for a very rigid structure. This technique is called laminating.
 
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#7
Ellipsa-1st-veneered.jpg


IIRC chris did 2 layers of rubberply. 1 of hardboard & veneer. Done with a vacuum press.

dave
 
#10
I`ve done it in a project - used a gym bar to bend the plywood and warm water. Problems you`d encounter unless you use extra screw pressure as on the first pic:

- Glue will not disperse even inside the two bent planes leaving cavities
- No matter how you do it, if no restricting form is used, you will not have the panels match perfectly on the x-axis. I knew this would happen and made them larger than needed, then had them cut with a saw which also clears problem 3 ( next one )
- When you bend them, the edges of the speaker panel would be made of varying 90 degree forms ( toothed as the plane is warped ). To later attach the front and rear baffles, you`d need these cut.

The easiest way to accomplish this is to first build a bending press that would keep the material tight and would allow for greater pressure. Do not underestimate plywood - a 900mm/40mm/8mm sheet would support your own weight without bending that much ( fulcrums at the very corners ).
Second easiest way is to use thin sheets of mdf - I used 4mm on this one, and glue them together, then bend to the desired shape. Once polymerised, the glue would keep them from returning to their original, straight, shape.
 

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#14
Evanc: I am in charlotte NC, and know too little about wood. I am tempted to take you up on that offer.
Charles Darwin: That columbia bending plywood - I will look into home depot today. They dont have it on the shelf. So hoping they can order it.

Thanks.
Srinath.
 
#15
Yeah bendy ply is the thing to go for, comes in different thickmesses which will allow you a tighter radius with the thinner stuff. The exterior stuff doesn't bend quite as much but makes a far more rigid finished product. I make all my speakers with this stuff. Brilliant stuff. Shame you aren't in the UK I'm just setting up a custom speaker building company 🙂
 
#16
Orangeart: LOL, I am building with B&W woofers, and likely a soft dome mid and a tweeter very similar to the B&W 801/802 matrix series.
Too bad, B&W parts are likely more easily and cheaply available in england too. Cos those B&W mid cabinets are $$$ around here.

Cool.
Srinath.
 
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