A hammer is a tool that delivers a discrete impact to an object; the object can be another tool that is powered by the hammer blow, such as a chisel (tool); an object that is moved by the blow (e.g., a nail (fastener) or a beam being forced into place); or an object to be disrupted by force (e.g., concrete to be shattered).
Muscle-powered hammers are among the earliest known tools, in the form of suitably shaped stones, but there is a wide range of specialized hand-operated hammers, as well as hammers driven by an external power source. "Hammer" has other meanings, actual and symbolic; a war hammer was an early refinement on a club (weapon), and it can be a symbol of force for good or evil.
Hand-operated hammers come in a great variety of sizes, shapes, and materials both of the striking surface and the parts of the hammer that direct force to that surface.
A basic hand hammer
A simple muscle-powered hammer is little more than a striking head attached to a handle. Assuming that both sides of the head are identical, there is still a great deal of variation. For example, a mallet (tool) has a head made of a relatively soft substance such as wood or rubber, and is used to drive other tools such as chisels, or to form sheet metal. The handle of a mallet is often fairly light if it is intended for reasonably precise work.
Perhaps the most common hammer is a carpentry clawhammer, which has a flat metal striking face attached to a forked metal claw for prying nails out of wood.
A sledge hammer is still a basic hammer type, but the striking head is of metal, and of considerable weight. Sledges intended for use with one hand might have a flat-faced steel head of 1-2 pounds (500-1000 grams), and be used for much heavier tasks, such as driving hardened nails into concrete or stone. The handle of such a hand hammer might be 12-16 inches (30-40 cm) long.
Another common hammer is the ball-pein, sometimes spelled ball-pein, intended for use on metal, especially sheet metal. It has a flat striking head, but the reverse is a metal ball that makes controlled dents in the workpiece.
Sledge hammers for heavier tasks will be wielded with two hands. The handle is longer, to allow swinging from over the shoulder, and the head is much heavier. For many tasks, the heavier the head, the more effective the hammer in applying force, but human strength limits its weight. People who do not use such hammers on a daily basis rarely can control, or even swing, a head weighing much more than 6-10 pounds (3-5 KG).
Refinements for applying force
In using heavier mallets against a tool or piece of work, there is a tendency for a hard blow to bounce back, perhaps damaging the work or presenting a hazard to the wielder. Rubber heads, which absorb shock better than wood, were one improvement.
A more sophisticated improvement is the dead-blow hammer. The head of such a hammer looks much like the basic cylindrical head, but is hollow. The cylinder is partially filled with loose dense material, such as lead shot. When swung, inertia moves the shot to just behind the striking surface and adding momentum, but the shot tends to dampen the recoil and reduce the tendency of the hammerhead to bounce away.
Refining the handle
Repeated hammering can cause repetitive stress injury. Proper technique is important, but cushioned grip materials on the handle reduce the chanc
Adding features to the head
Hammers used for nailing drywall have a curved or "crowned" striking head, so the head of the drywall nail will be recessed slightly below the surface of the drywall. The recess can thus be filled with spackling compound, a plaster-like material that can be sanded smooth, hiding the nail.
At the other end of the drywall hammerhead is a blunt axe-like blade, which helps in cutting drywall.
For maximum power and generally greatest comfort, hold handles near the base, and do not tense the wrist. Powerful strokes come from moving the entire forearm, or with sledges, the entire arm. For precision work, however, it may be best to hold the handle closer to the hammerhead, and use a tapping rather than a full striking mechanism.
When hammering small nails, it may help, when seating the nail, to hold it lightly in pliers, or even through a piece of cardboard. Once the nail is solidly in the material, but not hammered home, the cardboard can be torn free or the pliers released.
With hard wood or long nails, they may penetrate better if rubbed on soap, wax, or other lubricant before driving. If you use a semiliquid lubricant, be sure it will not seep and stain the work.