A hinge is a simple type of bearing that connects two objects, allowing them to pivot at the hinge. Most hinges allow movement along only one plane about a central axis, although naturally occurring hinges such as joints in the human body allow greater freedom of motion. Hinges can be constructed from multiple components that are joined together or from a single piece of flexible material.
Naturally Occurring Hinges
The most common naturally occurring hinges are joints in the body of an animal. There are many types of joints, but the hinge joint is the simplest. Hinge joints can be found on the human body in the fingers, toes, ankles, knees and elbows; however, the knee hinge joint is unique in that it also allows for slight rotation within the joint. The remainder of the hinge joints allow flexion only in one direction.
Leather is a natural material that has been used for hinges in the past; this type of hinge is called a strap hinge. The durability of a strip of leather and its ability to limit flexion to only one direction made it a popular choice for light doors and lids.
Piano hinges received their name from their original use: acting as a hinge that allowed someone to lift the top of a piano up. The hinges ran the entire length of the flat edge on the top of the piano. For this reason they are called continuous hinges. In contemporary uses, the continuous hinge runs the entire length of the two objects it connects. It is still used in piano construction, but it is also used in other applications, such as toolboxes, shower doors, gun lockers and folding wall partitions.
Butt hinges are the most common type of hinge. They are used on doors, cabinetry, windows and other types of furniture. Most butt hinges have eyelets that align to form a central cylinder. A lubricated bolt is inserted through the hollow of the central cylinder formed by the two halves. The bolt is positioned perpendicular to the hinge's axis of rotation and is the centre of the axis. Ball bearings sometimes take the place of bolts on heavy-duty butt hinges; these are used on heavier doors such as those that lead outside and also on doors that experience constant utilisation.
The barrel hinge is a simple type of hinge that is held together by gravity. One half of the hinge has a pin that sticks up vertically, and the other half has a hole that the pin fits into. The main benefit of the hinge is the ease of installation and the simplicity of its design. The respective halves are first affixed to the objects they will be connecting, and then one half of the hinge is dropped on top of the other. This type of hinge must be used in at least a set of two hinges.
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