Buying Lumber – Cup, Bow, and Crook

buying lumberWhat to Avoid when Buying Lumber at Home Depot

It goes without saying that the best way to avoid trouble when building a wood project is to start with lumber that is straight, flat, and square. Of course, woodworkers who own some of the more expensive shop tools have a definitive advantage in this arena. A nice wood planer, for example, can transform an otherwise crooked and twisted board into a perfectly straight piece of lumber – if you have the cash ($500+ for most models). Is this a practical investment? Maybe not, if all we’re talking about is building a few simple projects from pine. Not to mention that a lot of woodworkers avoid using planers with pine to begin with, for fear of gumming up their expensive blades with pine sap.

That leaves the rest of us with using boards pretty much as-is from the aisles of our favorite home center. The inherent problem here is that most of the lumber shelves at a big box store are riddled with boards that are warped and twisted. Not so much of a problem for carpenters who build houses and garages (there are workarounds for using warped lumber), and it’s not really a problem for the home centers either, since a good chunk of their business comes from the construction industry, not woodworkers. So the challenge for small-project builders is to figure out how to dig through the piles and pull out the best boards in the stack.

Sorting Through the Mess
Anyone who shops for lumber at a home center knows that the best boards in the stack are usually buried far below (or behind) all the rejected boards that no one else wants. Needless to say, this makes shopping for lumber awkward, time consuming, and downright dangerous for everyone (ever have a pile of 2x6s collapse on you?). I realize we’re all guilty at one time or another of being a little impatient (and careless) when shopping for lumber, but there is a better way to find the best boards available in the stack – without making a mess for the next person in line.

Good Cart / Bad Cart – The Smart Way to Sort Lumber
Whenever I head to the lumber aisle at my local home center, I immediately round up two carts. I call the first cart my “bad cart” and reserve it for the worst of the worst – boards that I definitely can’t use because they simply have too many defects. I call the second cart the “good cart” and reserve it for stacking only boards that I’m sure I want to take home with me. Sometimes I’ll even separate the good cart into two sides – a “definitely yes” side for boards that I’m certain I want to buy, and a “maybe” side for boards I’ll consider if I can’t find anything better.

Then, starting at the top of the stack, I carefully pull down boards one at a time, carefully examining each piece for bow, cup, crook, and twist (see definitions below). Each board then goes to it’s appropriate cart (good or bad) and I repeat the process till I’ve collected enough boards of acceptable quality for my project.
As you might imagine, going through this kind of sorting process can leave just many boards on the “bad” cart as the “good.” So what do you do with the rejects?

The best answer to this question might depend on the particular home center where you shop. Find a sales clerk in the lumber department, explain what you have in mind for sorting the lumber, and ask what the store’s preference is for dealing with the boards you won’t be taking home. I’m guessing most stores would rather you let the clerks deal with the discarded boards left on your “bad” cart, rather than you putting them back yourself. Most prefer to avoid creating more of a mess than they already have.

The Good, Bad, and Ugly – What to Look For When Sorting Lumber
Once you have a reasonable system in place for digging through the massive stacks of lumber (good cart, bad cart), the next step is to carefully examine each board for signs of cup, bow, crook, and twist. Here’s what to look for.

Boards with cup have a “U” shape from edge to edge, and are nearly useless for building anything. Why? Edges are where boards come together to form a joint. If a board is not super-flat along that edge, the joint won’t work – believe me, it just won’t. So the best way to check for cup is to lay the board flat on the floor and check for a side-to-side rocking motion. Then flip it over and check the other side. If it doesn’t pass the test, send that board to the bad cart.

Bow is easy to spot. It’s the same kind of “sag” you might see in an old bookcase shelf that’s been loaded with too many books. The best way to spot bow in lumber is to hold the board edge-side up, close one eye, and then peer down the full length. If you don’t see a straight line, the piece is warped from one end to the other. A certain amount of bow might be okay, though, especially if you plan to cut the board in small lengths. However, if you need the full length – for projects like a workbench or picnic table, send it to the bad cart and keep looking.

Unfortunately a board with zero cup and zero bow can still be crooked. Best way to spot crook is to hold the board surface-side up and peer down the full length of the board. A severe case of crook makes an otherwise straight board look like a road with a curve. Unless you plan to cut this board into a lot of smaller pieces, send this one to the bad cart and keep looking.

Other Lumber Defects to Watch Out For

Twist & Warp
Sometimes lumber defects are uneven and scattered. For example, you might find a board that is perfectly square at one end, but cupped on the other. Or maybe you’ll find a board that is surprisingly straight through most of its length, but then starts to curve a little towards one end. Although you might be tempted to quickly discard these boards, it might be worth your time to take a second look. Most project pieces call for relatively short lengths of lumber, which you can cut from anywhere on a board. That means not every board you bring home necessarily needs to be perfect (in fact, you might have trouble finding perfect boards in most home centers). The best approach is to bring your project design with you, and then look for boards that can yield just enough flat and straight pieces for the project at hand.

The word “check” is woodworking lingo for a split that appears at the end of a board, which can sometimes happen as lumber dries out. These boards can still be useful, as long you don’t need the entire length of the board for your project. Simply trim enough length off the end of the board to remove the split, and you’re set to go.

Knots & Voids
Pine can be riddled with knots and voids, especially in the less-expensive grades sold at home centers. The amount of trouble these kinds of defects might cause depends a lot on where they are located on the board. For example, a pine knot that is situated somewhere near the center of the board doesn’t really trouble me. In fact, it can even be nice decorative touch to the overall design, depending on the type of project your are building. However, I’m quick to reject boards that have knots and voids along the edges. This is a bad location for defects, because it’s exactly where we’ll do most of our joinery. Go ahead and buy the board if you can extract enough pieces with clean edges on both sides, otherwise set the board aside and keep looking.

A Final Note on Safety: Wear Gloves!
Getting a 3-inch splinter lodged in your palm while shopping for lumber will quickly bring your wood project to a screaming halt. Take my word – it’s not worth the risk. Always wear gloves when sorting through lumber. And if you’re not worried about splinters, then do worry about all the other sharp edges in the lumber aisle that cause just as much (or more) damage – like staples, metal banding, and sharp corners on warehouse shelving.

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