It wasn't long after I got my first digital calipers that I wondered how on earth I ever got along without them. Also know as electronic calipers, they provide very accurate measurements that would be impossible to duplicate with a tape measure or rule.
When first introduced years ago, electronic digital calipers were quite expensive and not everyone could afford to have a set in their home workshop. Most of the early models were sold to machinists and specialized tradesmen who embraced them and no doubt brought the price down for the rest of us.
The 6" calipers on the top cost me less than $20.00 and are just as accurate as the 8" set on the bottom that cost well over $100.00.
Nowadays you can pick up a set for less than twenty dollars that are accurate to plus or minus 1/1000". Try that with a tape measure or steel rule.
Today you can find these calipers made with a variety of materials. Metal, plastic and carbon fiber are the most popular materials from which they're manufactured.
I use the mm/inch button to quickly convert inch to metric and vice versa. Just set the desired measurement and then hit the button.
One of the features that I seem to use over and over again is the mm/inch button. Here in Canada we use the metric system, so a lot of what we buy is sold in millimeters and so on.
I often use the mm/inch button to do basic math conversions. If I want to figure out how many millimeters are in 1.250", I'll set the calipers at 1.250" and then just hit the mm/inch button. Presto... 31.75 mm.
If you want a really cool conversion calculator for your pc, try this free program from Josh Madison called Convert. It not only converts distances, but just about everything else too. You'll find it very handy.
Another great feature is the zero button. It allows you to zero out the reading anywhere along the scale. This lets you quickly see the difference in measurement between two boards or each end of one board. This works great for measuring in incremental steps too.
Taking an outside measurement on a piece of stock. Notice that these calipers measure to half of one thousandth as indicated by the 5 in the lower right hand side of the display.
The standard digital caliper can make four types of measurements; outside, inside, step and depth. Before you do any measuring though, make sure the measuring faces on the jaws of the caliper are clean.
Before I take a measurement, I'll wipe the jaw faces with a rag (my shirt) and then close the caliper to confirm it's at zero. If it isn't, I'll clean and try again.
If it still isn't at zero, I'll just zero it out with the zero button because by this time I'm pretty sure the faces are clean.
Taking an outside measurement is pretty straightforward, but you should be aware of two things that could affect your measurement. First, the surface of the workpiece you are measuring has to be as clean as your caliper's jaw faces.
Secondly, The digital calipers jaws must be square on the workpiece. I'll usually wiggle the calipers on the stock a bit while holding a little pressure on the thumb slide to set the jaws on straight. Don't overdo it with the pressure, too much force will give you an inaccurate reading.
Here I'm measuring the width of my miter slot to make a runner for a jig.
Taking inside measurements is pretty much the same as outside except you will be using the jaws on top of the caliper instead of the main jaws.
Just like when taking outside measurements, you can wiggle the digital calipers a bit to get a proper reading. Only this time put a little pressure on the thumb slide in the opposite direction.
You don't have to worry about dirty jaws so much with this measurement because the inside jaws are beveled in like a blade. This gives it the ability to measure the inside diameter of holes with more precision.
Measuring the height of my fence for a jig that will straddle it. I want the fence to be the same height from front to back.
The step measurement is great for measuring the height of ledges and well... steps. In the picture on the left I'm measuring the step from the base of my table to the top of my rip fence.
To make this measurement, I'll place the movable jaw's inside face against my rip fence, then slide the stationary or fixed jaw down to the table to get the measurement.
This is more accurate than using a depth measurement because of the wider surface area that the jaws have to rest on. Just make certain that both contact points are clean, and that the jaws are sitting flat and straight.
Here I am measuring the depth of my miter slot for the same runner as above. I could just as easily have used the step method here.
On the back of the caliper is a bar that is attached to the movable jaw. When the jaw moves out, so does the bar. This allows you to take depth measurements from the base of the scale.
Taking depth measurements can be a little finicky at times. The bottom of the caliper's scale is used as the jaw and there isn't much surface area to keep it from wobbling about.
You have to be sure that the caliper is straight and level to get an accurate reading, but a little patience and practice makes it easier.
The depth measurement works best for blind holes and other measurements that aren't possible with the step method.
In the picture on the right, it would make more sense to use the step method because there's lots of room to do it that way.
If you look at the tip of the bar you'll notice it's notched at the end. This is so you can measure with the bar flat against the wall of a hole and the tip of the bar away from the corner which might not be perfecly square.
If you don't have a set of digital calipers yet, get some. They're just too handy not to have around the shop. The small cost of twenty or thirty dollars is readily offset by the convenience they provide.
I appreciate your feedback. If you have any questions or comments about this article, please don't hesitate to contact me and let me know your thoughts.
A caliper with a movable jaw that is too loose or too tight will give inaccurate readings.
Most calipers have a couple of set screws on the top of the movable jaw that allow you to adjust the gib.
Simply adjust the srews until the jaw moves smoothly with no hint of play.