2. Materials Sheet goods from top to bottom: Exterior construction-grade, cabinet-grade maple, Russian birch, interior AC grade, exterior 3-ply, MDF and marine-grade okoume. Note the different smoothnesses of the surfaces.
and the type of arrangement on the sheet (e.g. book matched, slip-matched, random). Core materials If that wasn’t enough, then you come to the core materials which determine the structural properties of the sheet: Particleboard core looks like old breakfast cereal, a coarse mash of fibers. Compared to solid wood, it is inexpensive, not durable and not strong. Standard screws will not hold in it well. But for a panel inside a frame that has no stress on it, it’s perfect. Medium Density Fiberboard (MDF) cores are just as weak and inexpensive as particleboard, but it’s much heavier and denser. MDF’s advantage is its flatness—panels will look more “perfect” with an MDF core. 20
doormaking
Veneer and lumber cores are layers of solid wood plies. Structurally they are stronger and act more like solid wood than the manufactured materials. This means they move, though in odd ways (see next section), and hold a screw reasonably well (though not into the edges so well). Baltic or Russian birch is an entirely different sheet good product than standard cabinet grade plywood. It has thinner plies offering a more even look on the edge, though no structural advantages. The higher grades are “void free,” so the edges look even and can be exposed without looking too shabby. It more commonly comes in 5-ft. by 5-ft. sheets, but is also available in 4-ft. by 8-ft. sheets. For a captured panel, Baltic birch has no advantage, though it can be used to make a solid plywood door with nicer edges. Marine-grade plywoods are just that— used for boat building. These plywoods are waterproof, have no voids in the plies and are guaranteed to be structurally sound. While I’m not a boat maker, I have used marine grade plywood for exterior applications with good success, but still don’t recommend it. For flat panels in interior doors, I have no problem using veneer core plywood. I stay away from the MDF and particleboard cores as the advantages of a slightly lower cost and better flatness don’t outweigh the loss of strength and addition of weight. I also don’t use them in hollow core door construction for the same reasons. Call me a belt-andsuspenders purist. I’ve been called worse. Plywood adhesives Standard sheets of plywood use ureaformaldehyde resin glues. They are cheap, waterproof and really durable—except they outgas formaldehyde. How bad is it for you? Well, I just don’t know, but the government considers it a carcinogen (just like wood dust), so I take precautions. Just as I use a respirator, I keep my shop well-