“Measure twice, cut once” is an old carpentry saying you’ve undoubtedly heard at least one old carpenter say. That old saw is part of the wisdom of the ages. Trouble is, unless you know how to measure, you might find you’ve “cut it twice, and it’s still too short!” The world cries out for a reliable wood stretching tool but, to date, the technology eludes mankind.
I am reminded of a high-end cabinet installation I worked on with the lead finish carpenter. The design called for a 12 foot wide arch over the window at the kitchen sink. The wooden arch spanned the distance between flanking wall cabinets, a precise dimension. When the custom arch arrived, the carpenter attempted to install it only to discover it was 1/8 inch too long for the space between the cabinets. He decided to make an “executive decision” and neatly removed wood from the center of the arch, replacing the missing wood with a wooden carving to disguise the repair. Then he installed the furniture-grade “arch” on the wall. The owner came home, looked at the “arch” and said, “That’s not an arch!” True enough, when you remove the center of an arch and put it back together, the curvature of the arch appears “broken.” The owner demanded it be removed and replaced with the original design – an arch. The designer reordered the (very expensive) part; when it finally arrived, the carpenter measure its width, just to be sure. It was 1/8 inch too short for the space. Upon being informed of this by the carpenter, the designer fumed, “Well, can’t you just cut 1/16 inch off each end?”
Measuring can be tricky business. Some basic tape measure lore will help ensure your projects are the correct size and wasted time and materials are kept to a bare minimum.
The spring tape measure, patented in 1868, replaced the carpenter’s folding ruler as the favored measuring tool in the 1920s. Made of curved metal, it is designed to stand out when extended to allow control when measuring long dimensions. The tang on the end hooks the tape to the board as you pull out the tape. The tang also floats (moves) back and forth a distance equal to its thickness, to provide both inside and outside measurements that are accurate.
Whether measuring inside or outside dimensions, an alternative method to ensure accuracy is to “burn an inch.” To use this technique hold the tape with the 1 inch mark lined up with one end of the distance to be measured; over longer dimensions this step requires the assistance of a helper with a good eye and steady hand. Pull the tape to the other end of the measurement and read the tape, subtracting the 1 inch you “burned.”
When you’ve got your measurement using either method, measure again. “Measure twice…” at a minimum. Repeated measurements improve accuracy and skill. Who knew “pulling a tape” was a skill?
Your choice of tape measure(s) should be considered as carefully as any other selection of the “right tool for the right job.” Not all tapes are created equal. Some are too narrow to stand out (extend) very far without collapsing. Others have incremental marks that depict dimensions as small as 1/64 inch, which are extremely difficult to see and mark accurately. 1/16 inch gradations are adequate to just about any measuring task; if you absolutely need to measure to a 32nd of an inch, it’s not difficult to interpolate between the 1/16 inch marks. Tiny marks on a tape measure increase eye strain, especially if you are using your tape measure repeatedly. European cabinet accessory manufacturers sometime specify dimensions to the half millimeter, believe it or not; this is about the width of a grain of salt. The 1 millimeter mark on a metric tape measure roughly equates to a “fat” 32nd inch.
A “fat” 32nd inch?
Some woodworking tasks require exacting dimensions, meaning you cannot choose convenient dimensions like when you build a jewelry box of your own design. Examples include installing any kind of finished trim wood to other existing structures, like cabinets. Your measurement might be accurate, but “accurate” is a hair’s-breadth longer (or shorter) than your tape measure’s smallest mark. In this case, good practice is to call the measurement a “fat” 16th (or whatever), cut the piece long (fat) then test fit it. You can “sneak up on” the correct dimension by repeatedly shaving off a few microns until you get an exact fit.
By the way, the width of a typical circular saw blade “overhang,” also know as “side clearance” (the outside edge of the kerf), is on the order of 1/64 inch to 1/128 inch. On a miter saw, move the piece of wood to be trimmed to touch the flat part of the blade body (not the teeth) and then bring the saw into the wood; you can shave off tiny increments with each pass.
The easiest “rookie error” to make is to cut on the wrong side of the line you marked when measuring. It goes without saying you have just removed the width of the saw kerf from your original dimension. There are at least two ways to make this embarrassing mistake: using your circular saw line guide incorrectly; and forgetting which side of the cut is the keeper and which is the waste side. (A third related way is to use your circular saw line guide correctly, but to begin the cut from the wrong end of the pencil line, which puts the saw kerf on the keeper side instead of the waste side.)
Laying out studs when framing a wall can be done easily with a fat, flat framer’s pencil, the kind you sharpen with a small hand axe. On the other hand, finish woodworking, also known as fine woodworking, requires a more delicate touch. Whatever lead hardness you like to use – HB, No.2, etc. – make sure your pencil has a sharp point at all times. Look directly over the mark on your tape measure and draw a narrow mark on the wood in line with the line on the tape. Repeat this procedure on the opposite end if you are setting up a straight edge or scribing a pencil line to follow with the saw.
You can improve accuracy and precision by honing your skill at using a sharp pencil point to make your mark and setting your straight edge “right on the mark.” Trial and error will be a good teacher as to where the best match is between your pencil mark and the edge of the saw blade or the saw guide. If this sounds like splitting hairs, it is.
The placement of a straight edge saw guide relative to the line you want to cut is easy. Carefully measure the distance between the edge of your saw’s shoe on the wide side to the saw blade kerf. When you measure the size of the piece you want to cut, subtract and mark this distance on the wood. Do the same on the opposite end. The two marks are then used to locate the straight edge so the blade cuts on the outside (waste side) of the line as the shoe follows the straight edge.
It goes without saying all tools need to be set up and maintained for accuracy. Follow the manufacturer’s guidance for squaring up blade, table and fence; setting miter and bevel angles and stops; and any other adjustable parts of the tool. Check these routinely to discover and correct problems that arise from normal use.
Specialized measuring devices include calipers (inside and outside), scribing tools, squares (framing, rafter and adjustable), compass and story poles. A story pole is usually built for a particular task, like measuring vertical dimensions for a stairwell installation, such as minimum headroom. A scribing tool is used to scribe (draw or scratch) a line on one board that duplicates the shape, profile or edge of another board (or the wall), the objective being the two will eventually match when cut.
Finally, measuring is both a skill and an art: creating a finished piece of woodworking that looks perfect to the eye doesn’t happen overnight. Until you have become proficient at measuring and using your measurements confidently to build stuff, make trials and errors on scrap wood. If Carnegie Hall was the ultimate destination for a woodworker like it is for a singer or musician, you’d still get there the same way: Practice, practice, practice!