You will choose your primary wood, such as walnut, cherry, oak, maple, or one of the others such as those on the previous web page. But most furniture pieces also have a "secondary wood" - the wood that you don't see, inside the piece, for supports, guides, etc. One common secondary wood is poplar. Poplar is a durable hardwood, white, with a hint of green in the sapwood. It does not have a pretty grain nor does it stain well, so it is typically used for painted furniture, or as the structural parts of other furniture. Sometimes I get a good price on a "prime" wood such as ash or maple, and use them as secondary woods. Or occasionally I will "use up" odd pieces of primary wood such as walnut. You can be sure your secondary wood will be good quality and strong, but no promises what species it will be - it doesn't show!
Plywood is far more rigid and stable than most solid hardwoods. It is made from several thin layers of real wood, firmly glued together. The grain is oriented in different directions in each layer, to add strength and stability. The outside layers can be furniture grade woods, thus look and finish exactly like solid furniture wood, but the edges are ugly. The cost of prime furniture-grade plywood is comparable to hardwood (often $100 or so per sheet, not the familiar $20 per sheet for construction grade plywood). Plywood is used for it's other virtues, but not for economy.
Regular wood expands and contracts, especially across the grain (far more across the grain than lengthwise). Thus if the grain "matches," multiple pieces of wood can be glued together, but if you try to glue a piece of solid wood across the end of other solid wood, sooner or later that joint will break or the wood will split as the wood shifts. Each layer of plywood is so thin that the pieces can be glued "across the grain" and the overall panel has minimal expansion and contraction. Therefore regular wood can be glued to all sides of plywood, or (from another perspective) plywood can be glued into a wooden frame.
The unattractive edges of plywood need to be hidden, traditionally by gluing a thin veneer to the edge. If the design needs a shaped edge, I add a matching "real wood" edge that can be machined. Thus the labor saved by starting with large flat pieces is largely lost in hiding the edges, but plywood still has advantages in some uses because of it's strength and stability.
Over the years my experience has been that a bookshelf made of plywood will carry a far heavier load, with less sagging, than a comparable shelf made of solid wood. I recently saw some data that a solid oak shelf would carry a heavier load than plywood, although plywood was better than many other woods. Thus if you are considering an oak bookcase, you need to consider whether the shelves are regular wood or plywood. For other types of wood, I will normally continue to use plywood for the bookshelves. I will not use pressboard, MDF, OSB, or particle board for shelves.
Proper "solid wood" construction techniques require that the cabinet be built for the ultimate environment where it will be used... a chest of drawers for Maine would be different than a chest of drawers for Arizona. The problem is real enough that window and door manufacturers have factories in different parts of the country to support the local climate. In this mobile society we my unexpectedly need to move for our jobs, or choose to move for retirement. An excellent solution is plywood... a chest of drawers with plywood sides will be stable anywhere in the country. I am liking the good furniture grade plywood more and more, as a primary as well as a secondary wood.
Baltic Birch is a very special kind of imported plywood, often used for drawers. The outer layers are birch, which is smooth, white, and attractive. There are a larger number of layers for extra stability and strength (typically 9 layers rather than 3-5 layers in plywood 1/2 inch thick). The inner layers are good wood, without gaps or knots, so there are few surprises along cut edges. I usually recommend using the more stable "Baltic birch" for larger drawers, and a regular hardwood (which is more likely to shift with the weather) on smaller drawers, but will consider your desires.
I normally recommend plywood for drawer bottoms, for stability without excess weight. Plywood drawer bottoms can be "captive" - built into the four sides of the drawers. Solid wood drawer bottoms, such as aromatic cedar, can be used, if desired, but must be allowed to expand, normally by extending through the back of the drawer.
Fine furniture normally allows the wood drawers to slide on hardwood rails. The feel of the drawer is luxurious! But if the load is especially heavy (a pull-out liquor shelf) or the use is frequent (a desk or kitchen drawer is used far more than a dresser drawer) then metal drawer glides will be used. If you are concerned about wear on the bottom edges, a drawer "slip" can be added - an extra piece between the drawer side and bottom that stiffens the drawer sides and increases the surface area that slides on the drawer rails.
If the back will not show inside the cabinet, such as a chest of drawers, the back is normally made of an attractive plywood, with no attempt to match the rest of the wood. (I typically use birch or luan (like mahogany) plywood.)
if the back will show, such as a bookcase, the plywood must match the primary wood. Unfortunately it is virtually impossible to get thin furniture grade plywood with two good sides - the "inside" will match the rest of the furniture, but the outside will probably be ugly. If the bookcase goes against a wall, this is not a problem. But if the bookcase will be seen from behind, we need to plan a different type of back, both material selection and construction technique. The material may include a thicker plywood which can be bought with two good sides, although that will be more expensive and heavier.
Dust panels are sometimes included between some of the drawers used for clothing, to keep the lint and dust isolated. Since the load carried is only dust, and the panels cannot routinely be seen nor felt, manufactured wood products such as "Masonite" pressed wood panels are fine here.
A veneer is a thin layer of wood. Some woods are so rare that they are only available in these extremely thin pieces. Other fine woods (such as burls) need a solid base to provide strength. A complex design with one or several types of wood may only be practical as a veneer on a solid base. If a veneer is applied to one side of a solid wood base, a comparable veneer must be applied to the back as well, to minimize future warping.
Medium Density Fiberboard, MDF, is a man-made material consisting of many paper-thin layers of wood fibers. It is extremely smooth and strong, thus is a great base for wood veneer or paint. The weakness is that it is heavy - far heavier than solid wood. It can be destroyed by long-term soaking in water, so can only be used indoors.
Plywood is actually a form of veneer, and might be used as a base for veneer. Plywood can be made with glue that is adequate for interior use, or with special glues for exterior or marine use.
Particle board is basically sawdust glued into panels. Although it is strong, smooth, and inexpensive, I will not use it. Oriented Strand Board, OSB, is the next generation particle board, with strands of wood fibers, rather than just sawdust, glued into layers. It is great for construction, but I can't imagine where I would use it in furniture.
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