Precision Calipers Brookline MA
Jamaica Plain, MA
One tool can take all the guesswork out of measuring: a caliper. It's the ultimate in accuracy—for a woodworker, anyway—and it's easy as pie to use. A caliper reads out one precise measurement, clear and simple. Most calipers read in thousandths of an inch. They're designed for machine shops, not wood shops. Who measures wood in thousandths? Musical instrument makers, maybe, but not the rest of us. Fractions are what we want. A new generation of $30 to $50 calipers designed for woodworkers replaces thousandths with sixty-fourths. With one of these gems, you can easily make a measurement to the nearest 1/64 in. And you can go smaller yet, by reading between the lines, to about the thickness of a heavy sheet of paper. That's plenty good enough for wood, which can expand or contract that much each day with a change in humidity. Let's take a look at all the jobs a caliper can do, no matter what kind of scale it has. Then we'll weigh the pros and cons of five kinds of calipers—basic slide, vernier, decimal dial, decimal digital and fractional dial—you'll find in woodworking catalogs. Finally, we'll tell you about the clear winner, a $30 beauty that will pay for itself the first time you avoid a costly mistake.
Width of a Dado
A caliper measures an inside dimension, too, with small “reverse” jaws that can span a gap as narrow as 1/16 in. A caliper is a perfect tool for setting up dado blades. Using the reverse jaws, measure the width of a dado you've made; then use the other jaws to measure the thickness of any shims you must add to or subtract from the dado blades.
The most common use for a caliper is to measure an outside dimension, such as the thickness of your stock as it comes out of the planer. A caliper is a lot easier to read than a ruler for this everyday job. You can also measure the precise width of a board you've cut in order to adjust the rip-fence scale on your tablesaw.
Depth of a Hole
A small bar extends from the end of every caliper for measuring the depth of a hole. This bar may not fit in very small-diameter holes, however. The width of different calipers' bars varies from 1/8 in. to just over 1/4 in.
Depth of a Rabbet
Many folks are surprised to learn the back of a caliper can measure the width and depth of a rabbet or dado. In addition, whenever you use a zero-clearance throat plate on your tablesaw, you can measure the height of your blade or dado set with the back of the caliper. This is much easier than standing a ruler on end.
Read a vernier scale by using the zero to measure whole inches and sixteenths. Then find where two lines meet. This is the number of smaller fractional units to add, in this case, 1/128-in. units.
A vernier caliper is really clever. It has a sliding scale that replaces the dozens of tiny lines you would f...