It has already been established that the Vernier caliper is one of the most widely used measuring instruments after the measuring scale. The vernier caliper allows users to measure distances with a far greater degree of accuracy than a measuring scale which is vital in most engineering applications. The concept for the vernier caliper came into being way back in 1631 thanks to French scientist Pierre Vernier but it has been going strong since then.
The vernier caliper, like everything else has undergone modernization thanks to technological advancement and developed into digital calipers which are convenient and accurate. They also have many other useful features such as computer connectivity, the ability to compare lengths and to convert units of measurement with ease. However, manual vernier calipers are still widely used today and have some advantages over their digital counterparts. Firstly they are a bit cheaper than digital calipers unless you are talking about the high end market.
They don’t require a battery which makes them ready for use whenever required and the lack of electronic components also allows them to be able to function in harsher environments where digital caliper might fail or get damaged. In this article we are going to focus on the manual vernier caliper and discuss the important parts of the vernier caliper and their functions.
The upper jaws are the most prominent feature of a vernier caliper. These jaws are designed to grip objects firmly between them for measurement. One of the jaws is fixed and attached to the main scale of the caliper while the other one is attached to the vernier scale and is movable. The lower jaws allow the vernier caliper to measure outer dimensions of objects such as the length, width or diameter.
The upper jaws are smaller in size and are attached to the upper portion of the vernier caliper. Similar to the lower jaws, one of these jaws is fixed and the other is movable. The difference between them and the lower jaws is that the upper jaws are used for measuring inside dimensions of hollow objects such as inside diameters of pipes, lengths and widths of boxes etc. The jaws are placed inside the place to be measured and then opened till they touch the edges and the reading is taken at that point.
The depth rod is another useful feature of the vernier caliper which can be used to measure the depths of holes or steps. The depth rod is a thin rod located at the end of the main scale. To measure with the depth rod, the edge of the main scale is placed on the top surface of the hole and then the jaws are opened. As the jaws are opened, the depth rod slides out with the main scale. The depth rod is extended till it touches the bottom of the hole and the reading is taken as usual.
The main scale is the large scale which runs along the body of the vernier caliper. It is graduated either in centimetres and millimetres or inches depending on the type of units it is built for. In SI units the lowest graduation of the main scale is normally 1mm. The main scale is stationary.
The Vernier scale is the defining component of the caliper and what gives it its name. The vernier caliper is a smaller scale attached to the main scale and can move along the main scale as the jaws are opened or closed. The vernier scale provides accuracy to the reading of the main scale by further dividing the lowest reading of the main scale into increments. In a metric caliper, the vernier scale is divided into 50 increments each representing 0.02 mm.
The thumb screw is located at the bottom of the vernier scale. Its purpose is to provide a grip for the user to slide the jaws easily and adjust the position of the jaws and depth rod while maintaining a firm grip on the object.
The lock screw is used to fix the position of the jaws once the object is positioned properly so that readings can be taken without the fear of spoiling the position.