Buying Guide: What is Caliper?
Calipers measure the distance between two opposing sides of an object. They make inside, outside, depth, or step measurements, according to their type. Calipers are commonly used in architecture, metalworking, mechanical engineering, machining, manufacturing, carpentry, and medicine. The simplest calipers have two legs to mark the two points and require a ruler to take the measurement. More complex calipers use two sets of jaws instead of legs and have up to two graduated scales.
Types of Caliper
Vernier, dial, and digital calipers give direct and accurate readings and are functionally identical, having a calibrated scale with a fixed jaw, and another jaw with a movable pointer that slides along the scale.
- The vernier caliper has a scale sliding parallel to the main scale for an additional, fractional reading to improve measurement precision.
- The dial caliper has a circular dial with a pointer on a toothed gear rack replacing the second vernier scale. As with the vernier, this second measurement is added to the reading from the main scale to obtain the result. It is used also for measuring size differential between two objects.
- The digital caliper takes the same sort of differential measurements as the dial caliper by zeroing the display at any point along the slide, with an LCD (replacing the dial) that displays a single, easily read value in both English and metric units. Some digital calipers can hold data readings between measurements and send them to data collection devices.
Why I Need a Dial Caliper
Many long years ago when I began my machining apprenticeship – fitting, turning, machining to be exact – I learned to use and love my vernier calipers. They were quicker and more versatile than a micrometer. They could take accurate measurements of insides, outsides and depths to an accuracy of 1-thousandth of an inch – near enough – without any fuss.
Time marches on and instruments get refined and redesigned. Although that humble vernier caliper is still a common sight in workshops around the world, there are now two improved versions available: the dial and the digital.
Out of all the measuring instruments ever created for machinists and tool makers, one of the favorites and most useful is the dial caliper.
This precision instrument overcomes one of the setbacks of the original vernier design – the difficulty of viewing and lining up the thin etched lines on the vernier plate and handle by incorporating an easily readable dial. This 360 degree dial and needle is controlled by a high precision rack and pinion system.
Another problem that can occur with the original vernier caliper is a thing called ‘parallax error’. This happens when a critical reading is taken from the vernier scale without the eyes of the viewer being in exact alignment with the rulers. This can be overcome with careful focus and by moving the head around – but the dial caliper eliminates that problem completely.
Another useful feature of the dial is the ability to rotate the scale to any point so that a differential measurement can be taken – reading the plus or minus variation from a set size. Also, the caliper slide can be locked in place using a thumb-screw or lever to allow simple ‘go or no-go’ checks of manufactured parts.
There is no doubt that you can’t beat a micrometer when it comes to measuring parts to an accuracy finer than 1000th of an inch – or at those times when plus or minus 1 thou is critical. But to cover a wide range of sizes, you’ll need to get your hands on a whole set of expensive mics. The dial caliper on the other hand covers a large range of sizes, and has the bonus of directly taking inside and depth readings. This is what makes it so popular – and usually the first measuring instrument of choice for metal workers.
Caring for this instrument is mostly common sense. They are high-precision, delicate tools so they need to be treated with respect if you want long and accurate service from them. They usually come in their own soft or hard case – and it is a good idea to store them there when not in use. The teeth rack and gear mechanism especially should be kept clear of grime and foreign particles. As with all fine metal tools, a light coating of top-grade instrument oil will keep it operating smooth and rust free.
In the old days, with a young man’s eyes, I didn’t have many problems with my trusty vernier caliper. But today I’m grateful for the extra clarity and accuracy of that big ‘ol needle and fat dial on the modern dial caliper.
Check out the 6 Best Dial Calipers on the market right now:
1. Starrett 1202F-6 Dial Caliper
2. Mitutoyo 505-675-56 Dial Caliper
3. Fowler Full Warranty Stainless Steel Shockproof Dial Caliper, 52-008-712-0
4. Fowler 72-030-006 6″ / 150 mm Dial Caliper
5. Anytime Tools Dial Caliper 6″ / 150mm