I have read several books being a woodworking newbie and all. They all describe glueing and clamping of solid wood. However, none of them describe the process of glueing and assembling plywood.
Is there anything I need to do special? This is a 1.5(d)'x4'(h)x2'(w) @3/4" thick box. Its AC Plywood. Do I need to sand or route the edges before I put glue on them and clamp them? Do I need nails in addition to glue? The front of the box will actually sit in a hole framed with
2x4s. I will support that back with a small 2x4 pedestal.
Also the wood was sitting outside in detroit where its cold and dry. How long should it sit in my house where its warm and standard humidity before I cut it, or before I glue it?
It will have to be very very flat and smooth for a decent glue joint. Unless you are sure you can do that, you better plan on some mechanical aids; such as nails or supports.
I would have it indoors for at least a couple days before using it.
it's pretty similar to gluing solid wood. after all, plywood is made up of thin sheets of solid wood...
don't sand them if you can help it, and if you do, make sure you get all of the sanding dust off before you put the glue on.
for glue to work, the parts have to fit together quite well. you shouldn't be able to see light through a joint in 3/4" ply before the glue goes on.
if the glueup is perfect, no. if your jointery is even slightly less than perfect, or if you want to be able to pull the box out of the clamps before the glue is fully cured, or if you expect the box to receive stresses beyond the glue's performance characteristics and want it to fail a bit more gracefully, then use some nails. sometimes nails can make an assembly easier to get together- like when you need to fit several parts together, then turn the whole thing over, then fit several more parts together, all before you can get the clamps on. other times it's good to use redundant methods, like glue nails just to allow for a little sloppiness that may creep in to either method.
so no, you don't necessarily need both, but it's often not a bad idea anyway.
is that hole part of a frame wall? if so, the wall can provide a lot of strength. use shim shingles to fit the box (is it a cabinet?) into location. allow 1/2" or so between the box and the frame opening for the shims.
depends how long it was out there. if this is new plywood, clean and in good condition, a few days sitting inside might be enough. if this is used material, or has been weathered or is dirty, you are going to have more work to prepare it for use.
Glues fine, it's nails and screws into edges that it doesn't do as well as solid wood. They're often worse for having been nailed.
If it needs to support itself as in a real box, you should consider a a combination joint. Rabbet ends 3/8 x 3/8, dado sides 3/8 x 3/8 and as far from the edge as will bring the surface of the other flush or vice-versa if the static loading is on the sides. Easy stuff on a router table. Gives you some mechanical strength and twice the glue surface.
It's wetter outside than in. Wood sees _relative_ humidity. Check the weather report under relative humidity and see what the wood's experiencing. You should bring it in early to warm it enough to get good glue adhesion, and keep both faces open to the air.
Remember when you are designing your box that a glue joint to end grain has essentially no strength at all. Only long fibers glued to long fibers have any strength. And when you look at the edge of a piece of plywood, about
50% of is end grain wood. So, a glue joint will hold, but isn't the strongest.
The box is fairly big--if it is going to hold heavy stuff, you may want to reinforce your joints. Forget nails, they just hold things in place until the glue dries. If you use screws, be sure to pre-drill the holes so they don't split the plywood. Think about putting a glue block in the inside of the joint. That way you have lots of long grain glue surface and MUCH more strength.
Biscuit jointer, lots of clamps, white rubber mallet to assemble it.
These are the best clamps to have
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're aluminium extrusion and cheap, rather than strong. You can afford plenty (You Can Never Have Too Many Clamps) and they're lightweight enough that they don't make the box collapse or fall off the bench under their own weight.
If you're making a habit of simple boxes, look into a biscuit jointer. There's nothing quicker and easier.
3/4" is pretty thick for plywood boxes. Fine for coffins, might be a bit heavy unless you really need it. I prefer to use expensive birch plywood for 3/4" boxes, just because it's a bit lighter than cheap tropical plywood. Plenty of space for biscuits though.
You're going into end grain(sic) so nails aren't much use. Screws are far better, so long as you use modern (European ?) parallel thread woodscrews. Use single thread, not double.
The first thing I ever built was a TV stand out of recycled plywood shelves. It had shallow dados with the shelves glued and nailed in place' no back, no glue blocks. I was a little scared to actually put a TV on something so rickety.
Last year I was throwing it out, so I decided to see how much it would hold. I gradually put 200 pounds of steel chain on top; no problem. Then I fixed the bottom and "gently tapped" it sideways with a sledge hammer. I knocked it to a 30 degree angle before it collapsed. Presumably the glue had broken up long before that, and all that was holding together were the nails.
So, nails do add "some" strength; in this case, quite a lot.
Reread the thread. Part of what was being discussed was the strength of nails. In any case, lots of well made funiture has had nails used in the construction. Shaker funiture comes to mind.
Accepted. The fact that nails are used does not demonstrate joint strength, however.
Can you point to studies that demonstrate that a well formed and properly glued joint is any stronger when nails are used as well? How many nails in what area or linear distance? What size nails in proprotion to the dimensions of the wood?
It's been discussed to death here that a properly formed and glued joint will fail AFTER the wood on either side of the glue line fails.
If you can demonstrate that nails add strength to such a joint, I'd love to read the data.
Especially when used into the edges of plywood, where they often follow faults in the plies and peek out, or split the glue between plies and make the whole structure weaker. Mechanical joints, fully glued are the best.
Of course, glue lines, when they fail, do so catastrophically, a nail just sits there and bends.
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