An impact drill is a conventional hand tool equipped with an additional impact mechanism that allows for efficient drilling of masonry and concrete. The impact mechanism typically employs a cam arrangement to repeatedly move the chuck forward against spring pressure when the drill rotates. Drill bits used with the impact function of these drills are dedicated masonry or concrete bits with flattened, tungsten carbide tips. An impact drill may be used to drill into a variety of hard, aggregate materials such as brickwork, cement, and concrete. These drill types are available in a wide range of power ratings and include both AC (alternating current) and rechargeable battery models.
An impact drill is specifically designed for masonry and concrete as it combines a concussive, chiseling action in addition to the rotary motion of the drill bit. This hammer or impact action is typically achieved with a pair of cammed discs and a movable, spring loaded chuck. One disc is attached to the chuck shaft and the other to an actuator switch. When the drill is set on impact or hammer action, the two discs are pressed together. As the chuck rotates, the cammed surface of the discs force it forward and backward against spring pressure, thus supplying the hammer action.
The masonry drill bits used in an impact drill differ from conventional bits in several ways. They feature a flattened, tungsten carbide tip section which is generally slightly wider than the drill shaft. This tip acts as a chisel and responds to the concussive impact by chipping away the material rather than cutting it as a conventional bit does. The dust and chips are then carried out of the hole by the spiral drill shaft.
Impact drills are available in a wide range of sizes and designs suitable for most domestic and industrial applications. They may feature motor ratings as low as 250 watts and as high as 2,000 watts. Impact drill chucks are capable of accepting drill bits of up to 1 inch or more in diameter. Most impact drills are designed to run on AC power although rechargeable cordless models are also common. Many impact drill designs include multi-speed settings which allow for better control of the drill particularly when starting a hole.
The impact drill is only suitable for use on masonry surfaces; it should never be used with conventional drill bits. Due to the percussive forces involved and the inherently brittle nature of the materials drilled, this type of drill generates large amounts of dust and fine chips. For this reason, eye protection should be used at all times when operating an impact drill. Masonry drill bits should also be regularly inspected for excessive wear or damage to prevent injuries.