Measuring and Marking
Accurate measuring and marking are the bases of successful carpentry. A mistake in measuring often means wasted time and material. Though it may seem simple, good measuring technique does not come naturally. It takes practice. Don’t rush your measuring. Take your time and double-check your work. Adopt the carpenters’ maxim, “Measure twice, cut once.” No matter what measuring device you use, get comfortable with it and learn how to read it accurately. Many a board has met its ruin because someone couldn’t distinguish a inch mark from a 1/4-inch mark. Once you’ve made a measurement, don’t trust your memory. Jot down the figure on a piece of paper or a wood scrap. Marking, not reading, the measurement is the difficulty. Make a clear mark using a sharp No. 2 pencil, the thin edge of a sharpened carpenter’s pencil, a knife, or a scratch awl (especially if working with sheet metal).
Compare Measuring Devices - Odd as it may seem, different measuring tapes or rulers can differ slightly—differences that will show up when dealing with long spans of lumber. This can lead to frustration if you are calling out measurements for someone else to cut. Before you accuse your partner of sloppy cutting, compare measuring devices to be sure they’re calibrated the same.
Measure with a steel tape. A steel tape is the most popular measuring device because it does most jobs with ease. Note that the hook at the end of the tape slides back and forth slightly to compensate for its own thickness. This means that whether you hook the tape on a board end for an outside measurement or push it against a surface for an inside measurement, the result will be accurate. For the first few inches of most tapes, each inch is divided into 1/32 inch increments to facilitate extra-fine measurements.
Take an inside measurement. Where outside measurement is difficult (here the drywall is in the way of measuring between the outside edges of the 2x4s) make an inside-to-inside measurement. A folding ruler with a slide-out metal piece works best. Extend it, measure, and hold the slide with your thumb until the measurement is transferred. You can use a tape measure for such measurements, but it is difficult to be accurate because you have to add an amount to compensate for the length of the tape body.
Make a V mark, not a line. Marking with a simple line often leads to inaccuracies. By the time you’re ready to saw, it’s easy to forget which end of the line marks the spot—or where to cut on a thick line from a blunt pencil. For greater accuracy, mark your measurements with a V so you know precisely where to strike the cut line. To ensure pinpoint accuracy, place the point of your pencil at the V, slide the square to it, then make your line. If you need to extend cut lines across several boards, use a framing square. For longer lines, use a drywall square.
Mark for rip cuts. Need to mark a cutoff line along the length of a board or a piece of plywood? If the line is parallel to the edge of the board and accuracy isn’t critical, use your tape measure as a scribing device. Hold your tape so that a pencil laid against its end will make the correct line. Hold the tape and pencil firmly and pull evenly toward you, letting the tape body or your thumbnail slide along the board edge. For sheet goods, first mark the cutoff line at both ends, then snap a chalk line between the two marks, or clamp a straightedge in place and draw a mark.
Allow for the saw kerf. When you cut material, the saw blade reduces some of it to sawdust. So, when measuring, you must allow for the narrow opening left in the blade’s wake—called the kerf. Usually, a kerf is about 1/8 inch wide. If you’re making just one cut, account for the kerf by marking the waste side of the cutoff line with an X. There’s no confusion then as to the side of the line on which to cut. If you are cutting multiple pieces out of the same piece of lumber, make double marks to allow for the kerf. Otherwise, you will cut each piece too short.
Holding and Measuring in Place
The most accurate and mistake-proof way of measuring is not to use a measuring device at all. Simply hold a piece where it needs to fit and mark it. You can do this for a simple cutoff. At other times, such as when you need to cut a board in two directions, use a combination of techniques: Hold and mark, then measure. Often this method isn’t feasible, especially where access is limited or when the lumber being cut is too bulky to be held in place. But take advantage of this foolproof approach when you can.
1. To mark for a cutout, first measure the depth of the cut. When you need to cut a board in two or three directions to make it fit around something, begin by holding the board in place. Make a small mark showing where the cutout is to be cut to length. Then measure how deep the cutout must be by measuring the distance between the leading edge of the board and the place where it must end up once it’s cut.
Hold and mark for a cutoff. When you need to cut a board to length, begin by checking one end of the board for square. Press the square-cut end against one side of the opening, and mark the other end for cutting. To avoid distorting the measurement, don’t push the square-cut end into the space any more than needed.
2. Transfer measurement mark. Use a square to extend the length mark. With a tape measure, transfer the depth measurement to two places on the board—at the length mark and at the end of the cutout. Use a square to draw a line from the length mark to the depth mark. With a straightedge, mark a line between the two depth marks.
No-Mistake Measuring - Carpenters make measuring mistakes every day, so don’t be surprised when you do also. Here are some common mistakes and how to avoid them:
Sawing on the wrong side of the line. If you cut on the good rather than the scrap side of the line, the board will be 1/8 inch short. Always draw an X on the scrap side.
Misreading upside-down numbers. Is it a “6” or a “9”? Make sure you know.
Simply forgetting. Write down all measurements immediately, so you won’t forget.
Lay out a plate for a stud wall. When building a wall, the studs (upright 2x4s) must be 16 inches on center; that is, you want 48- or 96-inch drywall or paneling sheets to end in the middle of a stud. To make marks for studs, mark every 16 inches, minus 3/4 inch (15 1/4 inches, 31 1/4 inches, and so on). Measure over 1 1/2 inches and make another mark. Draw lines at your marks and an X between to show stud location.