Calipers are measurement tools that are used to measure the complex dimensions of an object where a ruler, tape measure, or any other measurement tool cannot be used. These dimensions include the depth, internal and external measurements.
They are also preferred for measurement by engineers and woodworkers because they give very precise readings. However, the tools come in different types and these are listed down below.
Different Types of Calipers
1. Digital Caliper
Digital calipers offer the latest in caliper measurement technology. Though they have ruler scales on the front side with measurements in cm, mm or inches, this is rarely used to take the readings.
Instead, the unit incorporates the use of a Printed Circuit Board (PCB) strip with copper lines, which is laid out below the ruler scale and it runs through the entire length of the slide beam. The reading head has a PCB with its own copper lines.
The combinations of these two copper line patterns create a variable capacitor, which comes into action as you slide the head over the ruler scale.
A microprocessor in the head calculates the difference in this capacitance then converts it into a measurement reading then displays it on an LCD screen.
This makes it very easy to use because it does the measurement and calculation for you, and gives the most accurate reading on screen.
For convenience, these tools have buttons for switching the measurement units, say from inches to mm, and zero setting functionality for eliminating the zero error or setting the reading to zero at any distance.
Other than that, the tool has a very similar appearance to a Vernier caliper, having inside and outside measuring jaws, and a depth bar for depth measurement. However, it is costlier because of the technology used.
2. Vernier Caliper
As stated earlier, a Vernier caliper has a very similar design to a digital caliper but lacks an electronic measuring system and an LCD screen.
However, it is equipped with inner and outside measuring jaws, as well as a depth bar for depth measurements.
This tool usually has imperial (inches) and metric (millimeters) scales and utilizes a movable graduated scale to get the measurement precisely down to the fractional level.
As such, it can give readings accurately to 0.01mm while normal scales usually go down to 0.1mm.
3. Dial Caliper
Dial calipers do have a main scale like in Vernier calipers, but the movable scale is in the form of a dial.
This dial makes it a bit easier to use because it has a pointer that shows the reading to the hundredths of a millimeter.
The main scale gives the reading in whole decimal numbers and combines with the dial to give measurement readings with a resolution of 0.01.
That said, this caliper has a depth bar, inner and outer jaws for measuring the depth, inner and outer lengths of objects.
4. Jenny Caliper
This tool is called an odd leg or a hermaphrodite caliper and is very similar to a divider.
This is because it works by pinning its sharp end to a fixed location on the surface while the other end measures the distance to the side/part of an object from the pinned point.
Some jenny calipers have a scriber on the measurement end, which can be used to make marks at a particular distance.
However, it doesn’t have a built-in scale. You have to transfer the measured distance to a ruler to get a reading.
5. Spring Joint Caliper
A spring joint caliper comes in 3 types: an inside caliper with outward-facing jaws for taking inner measurements, an outside caliper with inner facing jaws for taking outer measurements, and a divider caliper for measuring between two spots on a flat surface.
Regardless of the type, they have a common functional design, which includes the two legs/jaws, a spring that pulls them towards each other, and an adjustment screw/nut.
Measurements are taken by adjusting the screw to the point that the jaws contact the outer/inner surface of an object or the points on the flat surface.
The C spring at the top maintains tension on the legs while the screw holds them steady in position.
This ensures they don’t move and results in zero errors as you check the measurement against a ruler.
As such, this caliper is slightly better than a jenny caliper.
Micrometers are available in different types such as inside, outside, depth, inch, and metric micrometers. As the name suggests, they measure in microns (to the hundredths of a millimeter), which helps to enhance accuracy.
The measuring section is opened up by turning the knob on the thimble and this opens up the scale on the barrel.
This barrel scale gives the reading in whole numbers while the thimble scale gives the measurement as a decimal value to two decimal places.
Combined, you get accurate readings with a resolution of 0.01mm. However, this caliper is only ideal for measuring small distances.
As a summary, calipers are must-have tools for carpenters and engineers due to their precision measurement capabilities.
Though expensive, digital calipers are the easiest to use because they have digital readouts and are flexible enough to take inner, outer, and depth measurements.