Hammer drill

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A Hammer drill, also known as a "rotary hammer" or "roto-hammer", (see also rotary hammer 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. Lower power units are usually titled as "hammer drills". Higher power units, usually labeled "rotary hammers", tend to be larger and provide bigger impact forces. Modern units allow the hammer and rotation functions to be used separately or in combination, i.e., hammer mode, drill mode, or both. When used in the hammer mode, the tool provides a drilling function similar to a jackhammer.

A hammer drill is well suited for drilling holes in masonry or stone. It is also used to drill holes in concrete footings to pin concrete wall forms and to drill holes in concrete floors to pin wall framing.

A hammer drill can either be a drill (such as the one illustrated here), or it can be a replacement chuck that is installed on a power drill. When the drill is set to the "hammer drill" position it allows the chuck to move backward and forward over a short distance, allowing a spring to be compressed. When the spring is compressed, the chuck assembly is pushed as far back as it can go against a small eccentric flange. Any rotation of the chuck causes this flange to push back and reverse the direction of travel. The combined action of the spring, eccentric flange and rotation, push the chuck back away from the body of the drill at regular intervals. Under normal operation this sequence causes the whole assembly to "kick" with each turn, jack-hammering the drill bit into the material as it rotates. This helps to break up the masonry so that it can be removed by the drill bit's flutes.

[edit] Usage

The hammering action from the hammer drill can also be used as its name would suggest, as a hammer. For example, if you used a hammer drill to bore a hole in a concrete floor, you could then switch to the hammer setting, place an anchor bolt and "hammer" it in place by catching the bit directly on the center of the bolt.

Because of the jack-hammering action of a hammer drill, caution should be taken not to blow out the back side of the masonry/concrete where the hole is being drilled. This is especially true when drilling into a concrete roof deck; the jack-hammer action will "blow out" the bottom side of the concrete, leaving a golf ball size crater on the underside of the concrete.