As beautiful and fun to work with as solid wood is, it’s far from the only material a woodworker has at their disposal. Besides hardwood and softwood, there’s a multitude of sheet goods — materials made from wood in different ways — that have a variety of uses in the shop. Chances are you’re familiar with a few of these options, if not all, but occasionally it can be helpful to dive into the specifics of something familiar.
Sheet goods come in a wide range of types, but the ones we commonly use in woodworking can be split into two catagories: plywood and engineered wood (such as MDF and hardboard). As the name implies, plywood is constructed from thin layers (called plies or veneers) of wood. In contrast, engineered woods are the hot dogs of lumber industry. Off-cuts, shavings, and sawdust are collected, ground down, and bonded under heat. While they are cheaper overall, there are certainly different levels of quality, from the particle board used in box furniture to MDF and hardboard.
There are many kinds of plywood, varying in what kind of wood (or even MDF) that makes the sheet up, the thickness of plies (or veneers), and the number of layers within.
FLAVORS OF PLYWOOD
Plywood has been around for ages. However, the plywood we know and love today was first engineered by Immanuel Nobel (father of that Nobel), though it wouldn’t pick up in popularity until the mid-twentieth century. Plywood is cheaper than solid wood when comparing the same amount and species), and due to its cross-grain construction, it’s more stable against seasonal movement.
KINDS OF PLYWOOD.
Plywood can be divided based on how thick its plies are, and what they’re made of. Standard veneer core plywood is all wood, though there are two types we commonly use in the shop: “domestic” and Baltic birch.
The layers of a plywood panel alternate directions with each ply to keep the panel stronger and stable as humidity changes.
Domestic plywood may be veneered with any wood, but the interior layers are usually made from North American softwood (though you’ll see some birch slip in there as well). This plywood isn’t a bad choice, but it’s not my favorite. Baltic birch on the other hand is birch all the way through. As you can see at the bottom of the previous page, this wood also has thinner and more numerous veneers. While it’s a more expensive option than domestic plywood, I prefer Baltic birch for the look and strength.
In contrast to these are plywoods that involve MDF. MDF core plywood has hardwood veneers sandwiching a core of MDF. The advantage here is having a face that will stay smooth no matter the season while also getting the attractive look of the veneer.
Of course, MDF is heavy, and it doesn’t offer the same strength as veneer core. The answer to this was composite core plywood. By combining layers of hardwood with layers of veneered MDF, it seems to be the best of both worlds. Again though, there is a drawback. If exposed to sharp changes in humidity, the face veneers may check over time.
WORKING WITH PLYWOOD.
Overall, plywood is an easy material to work with no matter the kind. However, there are some things to consider when working with this type of material. First, whether making rips or crosscuts, I prefer a crosscut or dedicated plywood blade. The two photos show why. A blade with many teeth will be much easier on thin veneers than a usual ripping or combination blade.
The high tooth count of a crosscut or plywood blade results in crisp, clean edges, especially with thin veneers.
For routing, there a few bits you’ll want to keep on hand as well. Like a ripping blade, your typical straight bit will sometimes get in the a habit of chewing up plies and chipping out veneers. I’ve found there are two answers, which you can see in the illustrations below.
Spiral bits and compression bits will create a cleaner edge when working with sheet goods than your usual straight bit.
Figure 1 shows a spiral flush-trim bit. When shaping plywood with a template, these work great. The down-cutting flute gives a smooth top edge, while the template below backs up the lower plies. Figure 2 shows a compression bit, which has downcut flutes at the top and upcut flutes at the bottom to keep both edges clean. If I need to rout plywood, these are the bits I first look to. Plywood isn’t the only sheet good worth looking at though. Next up: engineered wood.
MEDIUM-DENSITY FIBERBOARD
The process of manufacturing MDF results in hardened exterior faces from the heat and compression they undergo.
Engineered wood is a modern marvel. While it may be heavy and plain, it has more than its fair share of uses. Additionally it’s quite inexpensive, and it makes use of otherwise wasted material. When incorporated wisely, engineered wood makes excellent templates and jigs, is a perfect substrate for veneer, and accepts paint wonderfully.
Though there are a number of engineered woods, the two I use most frequently are medium-density fiberboard (MDF) and hardboard. Both have similar composition, though they vary slightly in their manufacturing and their use.
WHAT IS MDF?
Medium-density fiberboard is a slew of chips, shavings, and dust from lumber mills that get dehydrated, ground into a fine powder, and heat treated to bond the fibers with resin (similar to what you see in the “dry process” on the next page). This results in a dense, wood-like board with a hardened outer shell.
MDF does lack the strength of solid wood, you’ll notice a difference when you use fasteners or need to join the sheets along their edges. However, with the right techniques, it’s a fantastic material.
JOINING MDF.
The illustration at the upper left shows the issue with using fasteners on MDF. The tapered body of a woodscrew, which draws solidwood pieces tight to each other, will instead wedge the MDF fibers apart. Additionally, any screw will cause the soft edges to pull up, separating the pieces rather than drawing them together.
To fix this, I use a sheet metal screw and a countersink on the underside of the MDF as well as the top. Sheet metal screws lack the tapered body, and the countersink provides clearance as the soft edge draws up. Figures 1 through 4 show how I accomplish this.
I start off by drilling a clearance hole through the first piece using a drill bit that is equal in diameter to the threads, as in Figure 1. This prevents the first piece from drawing up as the screw tightens. Next, I countersink both the top and bottom of the clearance hole (Figure 2). On the second piece, I drill a pilot hole using a drill bit that matches the core of the screw, leaving material for the threads to bite into, as in Figures 3 and 4.
To make sure the screw doesn’t split the MDF at the end of the pilot hole, creating a bulge in the side, I drill the hole just a little deeper than the length of the screw. Using this method is excellent for joining MDF panels that would lack strength if only glued.
HARDBOARD
The other engineered wood I use in the shop is hardboard. Hardboard is a thin, rigid panel with smooth and sometimes “waffled” faces. It’s no structural substitute for wood, but it has its own uses.
WHAT IS HARDBOARD?
The illustrations show the three processes used to make hardboard. Similar to MDF, wood fi bers are compressed under heat, though no resin is added — the natural cellulose and lignin in the wood strengthen and bond the fibers on their own.
At least one face of hardboard will be flat and smooth from the heated steel plate that compresses the board. The wet and wet/dry methods produce fibers that are oriented in two directions, resulting in a flexible board that easily accepts paint. The dry process orients the fibers randomly, which creates a more rigid product. Additionally, some hardboards are tempered. This is a process of coating the board in oil and curing the oil in an oven. This hardens the board even further and grants some resistance to moisture.
USING HARDBOARD.
The “waffle” pattern on certain types of hardboard is a natural result of the manufacturing method.
Because of its qualities, hardboard has some specific uses. The most common application I find is for guides, jigs, and templates. Whether it’s a bearing, a router base, or the workpiece itself, the hardboard provides a clean, rigid edge to register against. As an engineered wood, it’s also guaranteed to stay stable over time. In these cases, I prefer a dry-processed hardboard for its rigidity.
Dry-processed hardboard works well for templates, guides, and jigs. In contrast, hardboard made from the wet or wet/dry process is useful when incorporated into a project as paneling, or as splines to join two hardwood pieces.
Another common use for hardboard is paneling. These work well for the bottoms of drawers in shop projects, though I wouldn’t consider them “pretty” enough for use in home furniture without a bit of paint. They also make good center panels for doors or back panels for cabinets. Again, I’d keep these in the shop unless I planned on painting them.
The wet or wet/dry-processed hardboard is better here in my opinion. Not only are these types of board more flexible to accommodate the seasonal movement of solid-wood pieces, but they also take paint much better than their counterparts.
All in all, sheet goods are a versatile tool in the woodworker’s arsenal. As long as you know their limitations, the possibilities are sky-high.
