This story covers one of the most fundamental skills in carpentry: accurate measuring and marking.
Accurately transferring measurements is one of the most fundamental skills in carpentry. It's so basic, in fact, that most people assume they already know how to do it. But that assumption wilts when drywall has to be cut not once but three times, and every joint in the trimwork has a sizable gap.
First off, you need quality measuring tools. And you need to know the two key ingredients to accurate measuring: consistent technique and practice. Also knowing a few tricks of the trade can't hurt.
It's a good idea to keep the concept of accuracy in a reasonable perspective. For example, you don't need a perfect fit between sheets of drywall. A gap up to 1/4 inch is tolerable because the discrepancy will disappear under the tape and joint compound. If you're working with trimwork that will be painted, simply reach for the painter's caulk to conceal misalignments that are as wide as a hairline (or two or three). The acceptable tolerance level tightens up with clear-finished woodwork. But while absolute perfection is the goal, you also have to remember that you're building a house -- not a jewelry box.
Sizing the tape measure to the job is a sound ergonomic principle that will save effort every time you pick up a tape measure. Although the jumbo-size tapes have a macho appeal, you don't need a 25-foot tape to handle a 3-inch measuring job. Choose a smaller tape by feel: Select a case that feels comfortable in your hand.
Inside measurements can be tricky, but here's an accurate method. A folding rule with a brass extension is a time-proven classic. You can read the measurement, but it's quicker to simply mark the wood directly from the rule. Your tape measure's case tells the amount to add for the length of its body.
To transfer a measurement to the wood's surface, first press on the edge of the tape to roll the marks next to the wood. Put your pencil point at the line, and pull it away to the left. Repeat with another short line snapped to the right. The V shape is highly visible but its tip is small enough to retain accuracy. Stow a pocket-size pencil sharpener in your tool belt and use it often.
A mechanical pencil is a great tool for high-precision marking. Hold it upright at the point of the V mark, then gently slide the blade of your combination square up to it. Brace the square, then make your mark. To minimize mistakes, develop the habit of marking an X on the waste side of the cut.
Need to draw a circle? Here's a simple and accurate method that doesn't require a compass. Drill a hole in scrap material (something the dimension of a wooden ruler is ideal) for your pencil. After marking the radius (half of the diameter), lightly secure the other end with a nail. Now mark the arc with your pencil.
Modern manufacturing methods produce levels with impressive accuracy, but that quality takes a beating every time you drop the tool. Shocks can dislodge a vial's mountings and misalign the frame itself by warping or twisting. Here are a few tips on testing a level and preserving its precision.
Check your level's accuracy by placing it on a flat board on top of your workbench. Put shims under the board to center the bubble in the vial. Rotate the level end for end (don't flip it) and check the vial. Any error will be doubled. Some expensive levels can be recalibrated, but replacing the level is the usual cure.