by doug hodder » Sat Jun 30, 2012 9:02 pm
How you bend plywood kinda depends on the grade of ply you get and the radius you want to bend. There also is "bendable" ply. I personally would avoid that, it bends very easily, but there is not much strength to it and will seem soft. Ply with a lot of knots and voids may also be a problem. Typically on a 4 x 8 sheet, it bends easier on the width rather than lengthwise.
I've done some fairly sharp bends using baltic birch 1/8" and then doubling up on the layers so it ended up being 1/4" on a non clad trailer. I just sunk screws into it until the adhesive cured and didn't have to use straps and a ratchet type system to get it to bend. If you go 1/4" from the get go, it will probably need some finesse to get it to do what you want. Straps/clamps would probably be a good idea. Not all big box stuff is created equal and if it's got a high moisture content, chances are, it will bend more easily than a real cured piece. If you buy up a bunch and then don't store it correctly or use it quickly, it may take on a shape of it's own as it cures.
You can also soak the plywood with a blanket laying on it and dump hot water on it. That makes it tough on adhesives unless you are using a urethane type that requires moisture and the whole thing is a hassle, and for most curves, unnecessary. That's just my opinion however. If you were to go with a heavier ply, you could also cut a series of kerfs on the hard bend and that will assist on the bending.
Luan will work if it's going to be under an aluminum clad body, but for me, I wouldn't do it alone unless you want to put a ton of time and effort into burying it with epoxy. The Chinese crap will bend...then just when you think you got it where you want it...it may explode with a nice crack and expose the junk that the core is made of (appears to be Beijing newspapers and lawn clippings) at times...ask me how I know...It happened on a trailer for 2 profile and it wasn't all that hard of a bend.
You could also just google "bending plywood". There are a number of sites with ideas and techniques spelled out. Doug
