A hammer drill (or hammering drill) is a rotary drill with a hammering action. The hammering action provides a short, rapid hammer thrust to pulverize relatively brittle material and provide quicker drilling with less effort. These tools are usually electrically powered, and increasingly powered by batteries. The same technology is also used in electric "demolition hammers", also known as "chipping guns" or "breakers".
Lower power units are usually called "hammer drills," typically have a "cam-action" or "percussion" hammering mechanism, in which two sets of toothed gears mechanically interact with each other to hammer while rotating the drill bit. With "cam-action" drills, the chuck has a mechanism whereby the entire chuck and bit move forward and backwards on the axis of rotation, the motion is tied to the rotation of the chuck. This type of drill is often used with and without the hammer action but it is not possible to use the hammer action alone as it is the rotation over the "cams" which causes the hammer motion. These units are usually smaller and are commonly powered by cordless technology. They are not typically used for production construction drilling, but rather for occasional drilling of concrete or masonry.
Ancient China's principal drilling technique, percussive drilling, was invented during the Han dynasty. The process involved two to six men jumping on a level at rhythmic intervals to raise a heavy iron bit attached to long bamboo cables from a bamboo derrick. Utilizing cast iron bits and tools constructed of bamboo, the early Chinese were able to use percussion drilling to drill holes to a depth of 3000 ft. The construction of percussion drilling machines took more than two to three generations of workers. The cable tool drilling machines developed by the early Chinese involved raising and dropping a heavy string of drilling tools to crush through rocks into diminutive fragments. In addition, the Chinese also used a cutting head secured to bamboo rods to drill to depths of 915 m. The raising and dropping of the bamboo drill strings allowed the drilling machine to penetrate less denser and unconsolidated rock formations.