Why did my glued-up board warp?

[Tom Marchner]

I want to make two door stiles with bookmatched front faces. Each stile is to be 60 in. long and 3/4 in. thick.

I took a piece of quarter-sawn red oak and resawed in into two strips each 5/32 in. thick, 3 in. wide, and 61 in. long. They are of uniform thickness but a little bowed. But being only 5/32 thick they are quite flexible. These are to be my book-matched faces.

My plan was to create each stile by gluing one of these strips to a backing piece of red oak 5/8 in thick, 3 in. wide, and 61 in long. This shoould leave a combined board 25/32 thick which would leave me with a spare 1/32 in. which I could plane off. The backing pieces are perfectly flat and straight.

So for the first stile, I glued a strip to the backing by clamping them together on my workbench which is pretty flat. I used lots of clamps, spaced them evenly, used cauls to spread the pressure, and covered the entire board.

The result: the combined board bowed heavily. There is a 1/8 in. bow over the length of the board, way more than I could correct by jointing the board, rendering the board useless. The 5/32 strip is on the convex side of the bow.

My question: Why did this thing bow that much? Does glue make wood expand lengthwise that much? I thought that wood does not expand lengthwise to an appreciable degree. What I'm doing is pretty close to veneering although with thicker veneer than usual. Do veneer boards normally warp like this when the veneer is glued on?

The 5/32 strips are from quarter-sawn stock while the backing boards were not. I don't know if this could somehow explain it.

Thanks.

[harry strasil]

just planing one side of a board will make it warp, moisture in the glue stretches the glue side. lay a piece on damp grass with sunlight on the topside and see what happens

[Tom Marchner]

Harry,

When you say lay a piece of grass on it, exactly what do you mean?

[Gene Howe]

Moisture causes wood to expand. So, to take out the warp, apply moisture to the inside of the cup. I'd lay it on a flat surface with the convex side down. Soak some rags and lay in the cup. Then weigh down both ends. Leave it alone for a day, check it and apply more moisture if required. I've done this for plywood that's warped. A 6' wide X 36" long piece of 3/4 ply took a week to straighten in the heat of an AZ summer. I'm cheap or I'dve bought another piece of plywood.
I've heard that Downy in the water helps, but I've not tried it.

[Peter Quinn]

When you veneer ANYTHING you need to add equal thickness to BOTH sides of the substrate to maintain balance. On the bright side, the thing has failed now instead of after you are finished. I don't think its a generally good idea to use flat sawn stock, particularly oak, as a substrate for veneer. Not too stable. Might be better to create a stave core by ripping the flat sawn material into strips, gluing up to form your width so the core is in effect vertical grain. And definetly plane to veneer both sides of the core next time.

[J.R. Rutter]

Let it dry and see what happens. You've found the devil in the details: Wood doesn't move MUCH with the grain, but it does move SOME (apparently, ENOUGH).

[Paul Atkins]

Tom, lay the board on damp grass, not lay damp grass on the board. LOL By the way, I have straightened table leaves by this method.

[Tom Marchner]

I've learned a lot from this thread. I tried the wet rag method Gene suggested and sure enough it straightened out nicely. Peter's suggestion about putting the veneer on both sides of a board is probably a very good idea and I'll do that from now on.

Thanks for your good ideas.

--Tom

[David Perata]

Along these same lines may I pose a new but similar situation to you folks?

I need to build a cabinet door 12" wide X 55" long. The base will be 1/2" birch plywood and on either side of this base will be columns 3 3/4 X 1 1/4 X 55. These will be glued and screwed to the plywood.

Now, this door has to be perfectly flat when closed against the case. I've experimented with solid columns but they warped slightly. Of course they sat for a while but were in a humidity controlled room.

My next guess would be to make the columns out of 3/4" Baltic Birch plywood laminated to 1/2" ply to get the 1 1/4" thickness. This column would then be veneered with Bird's Eye maple.

Theoretically, when the plywood columns are glued onto the plywood base and clamped on a straight bench, they should dry straight. Right?

I know it's a tall door (55") and I also toyed with the idea of putting a metal spine into each column like a guitar neck to keep it straight. Be nice if it were somehow adjustable but I don't want overkill on this thing either.

The door will have three Euro hinges.

I've thought that in a situation such as this, the thicker columns will take the lead in making & keeping the 1/2" plywood base straight. As plywood doesn't really move that much, I thought that the glue will keep everything straight and tight. Maybe an epoxy would be a better adhesive.

Anybody use West Systems epoxy?

Any thoughts?

[Darius Ferlas]

I made 7' by 16" doors (rail and stile) and the warp is 1/8" between the top and bottom of the door. The material I used was laminated pine, 3/4' thick. The door was painted 5 coats of white oil paint.

So far so good. After two years the wood appears to be stable. The room's conditions vary from humid summers (sometimes with a/c on, sometimes not) to dry winters with humidity falling below 40%.

[J.R. Rutter]

Along these same lines may I pose a new but similar situation to you folks?

I need to build a cabinet door 12" wide X 55" long. The base will be 1/2" birch plywood and on either side of this base will be columns 3 3/4 X 1 1/4 X 55. These will be glued and screwed to the plywood.

Now, this door has to be perfectly flat when closed against the case. I've experimented with solid columns but they warped slightly. Of course they sat for a while but were in a humidity controlled room.

My next guess would be to make the columns out of 3/4" Baltic Birch plywood laminated to 1/2" ply to get the 1 1/4" thickness. This column would then be veneered with Bird's Eye maple.

Theoretically, when the plywood columns are glued onto the plywood base and clamped on a straight bench, they should dry straight. Right?

I know it's a tall door (55") and I also toyed with the idea of putting a metal spine into each column like a guitar neck to keep it straight. Be nice if it were somehow adjustable but I don't want overkill on this thing either.

The door will have three Euro hinges.

I've thought that in a situation such as this, the thicker columns will take the lead in making & keeping the 1/2" plywood base straight. As plywood doesn't really move that much, I thought that the glue will keep everything straight and tight. Maybe an epoxy would be a better adhesive.

Anybody use West Systems epoxy?

Any thoughts?

Don't expect solid wood glued to plywood (or plywood alone for that matter) to stay flat. Build it as a traditional door with frame and panel, even if you have to use butt joints with splines or biscuits. I'm no expert on them, but 3 Euro hinges would barely be enough for this, I would think. Maybe you could use magnets to get a nice flat closed appearance.

[David Perata]

Yes, I do plan to use magnets to suck the door into the frame.

1/8" warp from top to bottom wouldn't be allowable in my situation. I guess I will need to depend on magnets to do a lot of the job.

I didn't especially think that three Euro cup hinges wouldn't be enough. Maybe not. I will build a test door and if it doesn't work then four it is.