Digital Calipers - Canadian Woodworking Magazine

Shop Essentials: Dial calipers were once the domain of the machinist who needed to measure parts down to a resolution of 1/1000 of an inch. Woodworkers have been slow to adapt to these precision measuring tools. However, with the widespread use of digital electronics in manufacturing, there is no reason not to add an easy to use and inexpensive digital caliper to your tool arsenal.


Digital Calipers

A good quality dial or electronic caliper can be one of the best investments you can make. This multifunction tool can measure things as diverse as the inside measurement of a mortise, outside diameter of a dowel and the depth of a recess. It really shines when used to lay out your joinery and do your machine set ups; the days of guestimating will be over.

Using the calipers for most woodworking tasks is simple and straightforward, but learning to think in measurement terms based on the decimal system can often be more challenging. As your woodworking progresses and you strive for greater accuracy you will find it easier to work in decimals than in fractional units. This is especially true when working with wood you have milled to non-standard thicknesses and are then adding and subtracting the measurements. When woodworking, the natural tendency is to think of fractional values when using inches and the change from inches to decimals can take some getting used to. You’ll find it handy to tape a decimal-to-imperial conversion chart to your shop wall.
Dial Calipers
Most quality dial calipers are made of hardened stainless steel for long-term accuracy, although inexpensive versions made of plastic are available. It stands to reason that as the price goes up, the quality of the tool increases as well, and with calipers this old adage holds true. An inexpensive plastic caliper is still better than none, but it can’t compare to the mid or high-end models. Fortunately, the operating specifications of dial calipers made by the major manufacturers are comparable; it is the features and ease of use that sets the various models apart. Budget models have rougher movements, and can lack a thumbwheel adjuster or a reliable lock. Premium models offer silky smooth operation with a comfortable thumbwheel making adjustments down to .001" absurdly easy.
Precision Tools Need Precise Care
Calipers are precision measuring instruments and should be kept clean and free from grit and dirt; they usually ship with a case and should be stored there when not in use. When you take the caliper out, check it over and remove any dirt from the jaws, blade or depth rod and then slide the jaws to the left and close the jaws completely. Check to see if the dial is calibrated. If the indicator is centered on the 0 point then it is set correctly. If not, loosen the bezel clamp screw and adjust the dial so it is set properly and tighten the screw. As you move the jaw to the right the indicator will travel around the dial. Each inch is divided into tenths on the beam, and the distance between each of these 1/10th inch marks is then further divided into 100 divisions that are shown on the dial. To arrive at a measurement, read the hatch marks on the beam to the last full one and then read the dial value and add these two numbers.
Electronic Calipers
Like all things, modern electronics have changed dial calipers forever. Electronic units are even easier to use than the dial counterpart. The need to interpret a dial to arrive at the measurement is gone and the value is presented directly on the digital display. When using these units, close the jaws completely and turn the unit on. This sets the display to zero and you are ready to measure. The 8" Mitutoyo Digimatic has the ability to switch at will between displaying values in inches or millimetres. The most recent generation of calipers, like the Wixey, allows you to display the values in fractional terms as well. The mechanism inside the caliper still operates as before but when the value on the display is within .002 of a fractional value, an additional display indicates the fractional equivalent of the decimal reading.

Once you’ve begun to use calipers you’ll find all sorts of things to do with them. Here are some uses that we’ve found.
• The Freud dial-a-width dado set is adjusted using a dial where every click on the adjustor makes a .004" adjustment. After setting up the correct number of chippers, make a test cut in some scrap. Measure the thickness of your stock, zero the caliper, and then measure the width of the dado you have cut. Divide the result by .004 for the number of clicks to make on the dado set to obtain a perfect fit.

• The caliper can be used for simple comparisons as well, even without the display. If you mill your own lumber using a thickness planer and need to match the specific thickness of some existing part, then just measure the part and use the caliper as a simple 'go/no-go' gauge.

• If you use a variable spacing dovetail jig, like the Leigh D4 or the new Super Jig, a caliper makes symmetrical and custom spacing lay out a breeze. Setting the bit projection with the calipers makes it unnecessary to rout test cuts.

• When cutting a groove or dado on the router table make a test cut and then measure the depth with the caliper’s depth rod. Use the dial on the router lift, or the above the table adjustor, to easily dial in the difference as marked on the scale.

Making a depth measurement

Measuring an outside width

Measuring an inside width
When using these tools for your layout work and machine set-up you will need to abandon the humble pencil in favour of a marking knife. The lines left by the pencil are simply too wide to use with a caliper without introducing errors. When buying a set of digital calipers, invest in a Veritas Striking knife and an engineer’s square as well.

Using the new digital calipers when measuring and laying out your joinery will bring a new level of accuracy and precision to your work, and instead of complicating the process, it will actually simplify and speed up your work.