Replies

1. 
   JohnWW | Dec 02, 2003 09:25pm | #1

   Nick,

   Definitely sounds like a formula for trouble, it would be impossible to make a solid wood panel of that size and thickness stay flat.

   I'd try to talk the customer into sliding raised panels or better yet, hinged doors.  There's a reason why sliding doors are rarely used even though they are fast to make and require minimal hardware, sliding doors just don't work all that well and aren't as convenient.

   John W.

2. 
   woodrae | Dec 02, 2003 09:25pm | #2

   Nick—

   The quick answer: At 18 in., your doors will warp if made in solid wood.

   It may be a little, it may be a lot, but warp they will. Any panel made from solid wood will react to moisture changes in the atmosphere, with subsequent dimensional changes. No amount of finish can completely stop this process. If this dimensional change is not perfectly uniform across the panel’s width, the result will be some form of curvature, or warp. And my bet, without seeing your design, is that even a small curve in your doors will result in them binding in their tracks.

   Before getting into building options, let’s talk about design. One issue here is your proportions. At 18 in. wide by 30 in. high, the doors will likely have a tendency to tip along their tracks, and thus stick—especially if they’re just moving by their own weight along a bottom track. And a racked door will frustrate the user no end. Is there any way you could divide the total amount of doors less, so you end up with an arrangement of wider doors where each has a wider stance relative to its height? The longer the width relative to the height, the less tendency to tip.

   Another concern is the way you track the doors. You didn’t mention what kind of “tracks” you’re using. The traditional approach is to house the doors in a relatively shallow wooden groove in the case bottom, with a deeper groove at the case top, with enough extra groove depth at the top to install the doors and remove them when necessary. This method works well if your door proportions are taken into account. But with tall doors, perhaps you should think about hanging them on hardware to overcome possible racking.

   As far as building goes, you could chance it and build the panels from truly quartersawn stock (where the growth rings on the end grain are arranged perfectly perpendicular to the face). This arrangement will have the most uniform dimensional change. However, any slight irregularities in the grain—a small knot here, a swirl there, any number of other possible grain anomalies, all of which are quite common in birch—and the doors will warp, or twist. For practical reasons, this is probably not a good idea.

   If you must stick with solid, 1/4-in.-thick panels, I think you’ll need to find a way to brace them across the grain. You can inlay “blind breadboards” inside the panel, arranged crossgrain at each end. Cut a kerf, or slot, in the panel for each breadboard using an 1/8-in. slotting bit on the router table or, better yet, by ripping an 1/8-in. kerf on the table saw. I’d make the slot about 2 in. deep. Then install an 1/8 x 2 in. long-grain stick into each slot. Glue the stick in the center only, and pin it at the outer edges. This way, wood movement won’t be an issue and the panel can expand and contract without being bound by the stick. The downside? You end up with sticks that are only 1/8 in. thick—not real stiff for keeping the panel flat.

   A better approach would be to brace the back of the doors. You can add two or even three sticks per panel, each perhaps 1/2 in. thick. Again, like the breadboard, glue them only in the center of the panel and pin the edges. Of course, the potential problem here is that the braces may interfere with the action of the doors as they slide past each other and the cabinet.

   Now, here’s another idea: Why not make your own plywood? You can bandsaw three sheets of veneer from solid stock, each perhaps 3/32 in. thick, and glue them together with the middle layer crossing the direction of the outer layers. You’ll end up with only two glue lines on the doors’ edges. Or buy some premium, matched sheets of commercial birch veneer and lay them up in sufficient amounts until you reach the desired thickness, making sure the stack is made of an odd number of layers so the panel is balanced. Either of these constructions will create a stable panel. If you glue up the panel flat, it should stay flat. However, I’d make a few extra panels and let all of them sit free-floating in the shop for a week or so after glue-up to see which ones remain flat. If you choose your material carefully for grain, color and tone, you can make the doors blend in with the customer’s existing woodwork.

   Finally, you should consider the traditional approach: a frame-and-panel door. This time-honored method was devised precisely for the problem you’re trying to overcome: wood movement. If you make the frame straight, flat and relatively narrow—say, 2 in. or so in width—and house within the frame a solid panel of wood floating freely in grooves in the frame, the frame will remain flat while the panel is free to expand and contract while being kept flat by the frame. I know: you’ve probably considered this technique already and discarded it for aethestic reasons, but I thought it would be worth a mention.

   —Andy

3. 
   Alan | Dec 04, 2003 04:33am | #3

   Nick,

   It's not necessarily the case that these doors will distort with changing conditions.  If you completely encapsulate the wood with something that is impenetrable by water or water vapor, the wood will not distort--at least will not distort because of a change in moisture content.

   Epoxy is completely impenetrable by water and water vapor.  If every little bit of the doors are completely covered with epoxy the moisture content of the doors will not vary.  So if the doors are flat, and their moisture content is evenly distributed within the wood, changes in the humidity of their surrounds will not cause the doors' moisture content to change.

   You must be sure to completely encapsulate the wood.  Even one little "leak" can (can, not will) ruin it.  This means that any screw, nail or any other penetration through the epoxy must be re-epoxied to maintain the integrity of the barrier.

   You don't say how the customer wants it finished, but epoxy will take most any film finish or paint.

   Alan