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What is a Caliper?
Many building projects — whether they’re for personal home improvement or a day on the worksite — will require a caliper. This device is used for measuring the dimensions of an object, so you can make sure everything fits perfectly and finish the job without flaws. There are multiple types of calipers, each with its own purpose. Learn how to use them all, and you’ll be acing your projects.
For centuries, man has relied on the caliper to provide measurements of an object’s thickness and diameters. The oldest caliber was found in a shipwreck near Italy dating back to the 6th century BC. Our consistent application of this measuring tool shows that the caliper is a reliable source for measuring dimensions, and one that’s worth having in any tool box.
The layman will do well to have a caliper available for any home improvement project, but calipers play an important role outside of ambitious self-renovations, as well. They’re used in many specialized fields, including woodworking, metalworking, forestry, science, and medicine. Most commonly, calipers are found in engineering and science labs, where precise measurements are of the utmost importance.
Although there are many different types of calipers, most work with the same mechanics. Almost all caliper types resemble a ruler — a strip with a scale of measurements — with a set of upper and lower jaws at the left end. These jaws screw open and closed, and as they adjust a slider that is attached to the right jaws moves along the scale.
At the opposite end of the scale, there is a small, protruding rod that moves with the slider and the jaws. This is called the depth rod, and it can be used to measure to depth of holes.
The slider and jaw location on the scale is what provides the measurements, but the way that you read the measurements will vary depending on what type of caliper you are using.
Most calipers of this style have a thumb screw located at the bottom of the slider, which makes it easier to control the movements of the jaws. There’s also a lock screw at the top. This piece secures the position of the jaws and slider, so that you can read the measurements without accidentally moving the jaws, or compare the measurements to another item.
Calipers can measure both the outside and the inside dimensions of an object. The larger set of jaws — located on the lower side of the instrument — are made to measure the outside of something. The object goes inside of the jaws, which tighten around its width or length.
A smaller set of jaws is located at the upper end of the lower jaws. This part of the caliper is made for measuring the inside of an object, like the diameter of a slot or a hole.
The vernier caliper is the most basic of this instrument, but arguably the most reliable. This type of tool features two different rulers, one with the main scale and one with the vernier scale. The main scale is at the top, and the vernier scale is at the bottom. Each mark on the main scale represents one whole millimeter. The zero mark on the vernier scale will mark the number of millimeters for your measurements.
It’s simple to read the measurement in millimeters if and when the zero mark is exactly on a millimeter line. However, since most measurements won’t be to an exact millimeter, you’ll need an additional form of measuring.
That’s where the vernier scale comes in. The scale goes from 0-10, sometimes with smaller markings in between. Each main mark on the vernier scale represents a tenth of a millimeter. If the zero mark does not line up exactly, another of the 0-10 marks on the vernier scale may, and this will tell you the exact, fractional measurement of the item. For instance, if the “6” mark lines up exactly, that would indicate an additional .6 millimeters for the overall measurement. Some vernier calipers have even more precise measurements — like .02 millimeters — and will have additional markers on the vernier scale.
Vernier calipers are extremely precise and more reliable in the long term because of their simple design. However, the reading can be tricky for some people, so those that don’t want to perform the careful mathematics needed to read the scales will do better with a dial or digital caliper.
Dial calipers work just like vernier calipers in that there are two sets of jaws, a slider, and a scale for measuring. To use it, you place the item you want to measure inside the large jaws or outside the small ones, and move the slider to open them until they are tight. The difference here is that, instead of using the main scale and the vernier scale to get the measurements, you just look at the dial. The dial on these calipers uses a needle to displace the measurement within a fraction of a millimeter. You use this information, along with the scale, to get the final measurement.
Dial calipers are easier to read than their vernier counterparts, but since there are more mechanics in these tools they’re also easier to break and more complicated to fix.
Digital calipers are the easiest to read of them all, as they substitute the analog dial with a digital display. This electronic measuring tool works by using a linear code, rather than a rack and piston. The linear code reads the position of the jaws, calculates the measurement, and displays it on the screen for easy reading.
You use a digital caliper just as you would a vernier or dial caliper. The method of reading is the only thing that’s different. It’s straightforward and requires no math. Many digital calipers let you choose whether the measurements are displayed as millimeters, centimeters, or inches.
The one downside to a digital caliper is the battery. As with all electronics, this tool can run out of power, which would leave you stuck without measurements until you go to the trouble of replacing the batteries.
Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.
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