: Thanks to all the responses to my question. I believe I'll try a box beam
: even though it sounds like more work. Plywood comes in 4'X 8'and I need
: 16', so do I just offset where the sides join so I don't have a joint
: going all the way around at one spot?
: Thanks, James

You can do that, or you can combine two 8-foot long strongbacks
with a 3 foot length of solid wood. If you use bolts to hold this connecting piece in place you can later remove it. That makes it a lot easier to store the two strongback setions. Just stand them on end and stick them in a corner

To reduce sagging, put on more legs. A simple 2x4 leg attached to the center of a strongback provides a lot of support. If the stongback is more like a swayback, then add more legs.

Also, consider buying your plywood in pieces. a lot of big-box homeenters, and lumber yards have panel utting saws which make quick work out of ripping long pieces froma plywood panel. Usualy yuoou'll get one or two cuts for free, and then they'll start charging a nominal fee.

If you get them to rip four 4- or 6-inch wide strips from your plywood, and 4 more which are 3 inches wide. You'll pay a premium of about $2 ( That would be at 25 cents a cut), but you'll have the material is pieces small enought to carry and to shove into even a compact car. Saves a lot of time, too.

Another thought is to jsut buy an engineered-wood I beam, such as an I-joist. They come in lengths which would serve the purpose, but may need to be special ordered. At $2 a foot a 16 footer would be $32. (atually, they may be much less expensive than this-- but I'm just giving an example). That may be more than the plywood, but if you add in the oost for glue and screws, or other fasteners -- and your time -- the wood I beam might be a better deal for you. It is one piece and ready to go.
Just a thought or two.

PGJ