How Nail Guns Work

If you're hanging pictures or putting together a bookcase, a hammer is a perfect tool: simple, cheap and entirely effective. But if you're building a two-story house, installing hardwood floors or running your own furniture repair shop, you may want to spring for a nail gun. These powerful machines launch nails at high speed, fully embedding them in a piece of wood in only a fraction of a second. Obviously, such a machine can save you hours of toil and sweat. They take almost all of the work out of nailing.

In this article, we'll find out how these popular machines launch nails at such astounding speeds. As it turns out, there are a wide variety of nail guns on the market, employing a range of physical principles.

Spring-loaded Design

At its most basic level, a nail gun has only two jobs:

It needs to concentrate a great deal of hammering force into a single mechanized blow, which can be repeated rapidly.
It needs to load a new nail after the previous nail is ejected.

There are any number of machines that could handle these tasks. Since we can't look at every single model, we'll investigate a few representative designs.

The simplest nail guns use ordinary springs to generate the hammering force.

Here's what happens when you pull the trigger:

The triangular cam turns, pushing down one end of a lever (c).
The lever pivots, pushing up on the hammer (d). As the hammer pushes up, it compresses two springs (e).
The hammer has a small knob (f) attached to one end. As the lever pushes the hammer up, the turning scooper plate catches hold of this knob. At the same time, the rotating cam (b) releases the lever, which releases the hammer. The hammer is now held in place by the scooper plate.
As the scooper plate turns, it lifts the hammer higher and finally releases it.
The two compressed springs drive the hammer downward at high speed. If a nail is in position, the hammer launches it from the gun.

On the next page, we'll take a look at the nail-loading mechanism.

Nail-loading Mechanism

The gun in this diagram uses the most popular sort of nail-loading mechanism. The nails are glued together loosely, in a long strip. This nail strip loads into the gun's magazine, which feeds into the "barrel" of the gun. Springs in the base of the magazine push the nail strip into the barrel. When the hammer comes down, it separates the first nail from the strip, driving it out of the gun and into the wood. When the hammer is cocked back, the springs push the next nail into position.

One advantage of this system is that the glue helps secure the nails. When the nail is hammered into the wood, the intense friction heats the glue to the melting point. Once the nail is in place, the glue quickly hardens again, fusing the nail to the surrounding wood.

In this gun, the electric motor only cocks the gun; the coiled springs do the real hammering work.

Electromagnetic Design

One effective hammering device is a solenoid. A solenoid is a simple sort of electromagnet used in a variety of machines.

If you've read How Electromagnets Work, then you know the basic idea behind electromagnetic devices: Running electricity through a wire generates a magnetic field. You can amplify this magnetic field by winding the charged wire in a coil. Just like a permanent magnet, an electromagnetic field has a polar orientation -- a "north" end and a "south" end. If you put two magnets together, the north ends repel one another, as do the south ends, but the north and south ends are attracted to each other.

In an electromagnet, you can alter the orientation of the poles. If you reverse the flow of the current, the north and south ends of the electromagnet switch places.

A solenoid is an electromagnetic coil with a sliding piston inside it. In a nail gun, the piston is made of magnetic material. When you apply current one way through the coil, the electromagnetic field repels the magnetic piston, pushing it out. But when you reverse the current, the polar orientation switches and the electromagnet draws the piston back in. Some solenoids have a spring mechanism to draw the piston back in.

An electromagnetic nail gun uses such a solenoid as a hammer. When you pull the trigger:

The electrical circuit runs the current through the electromagnet so that the piston extends downward. Typically, the piston is attached to a sturdy blade.
The blade makes contact with the nail, forcing it out of the gun.
At the bottom of the cylinder, the piston hits an electrical switch.
Throwing this switch reverses the electrical current running through the electromagnet. The electromagnet draws the piston back in for another hit.

Solenoids are effective and reliable, but they are somewhat limited in power output. A solenoid gun may not be able to drive a nail through tougher substances, at least not in a single blow. In the next section, we'll look at a more powerful type of nail gun that has dominated the market.

Pneumatic Nail Guns

The most popular sort of nail gun is the pneumatic nailer. In these machines, the hammering force comes from compressed air, typically generated by a separate gas-powered air compressor. A standard air compressor works on the same principle as a water pump. It has one or more piston cylinders, which draw air in from the atmosphere on the upstroke and push it out to the gun on the downstroke. This generates a constant supply of compressed air, which flows through a hose into the gun's air reservoir.

A pneumatic nailer uses the same sort of hammer as a solenoid nailer: It has a sliding piston that drives a long blade. When the air pressure above the piston head is greater than below it, the piston is forced downward. When the air pressure below the piston is greater than above it, the piston stays up. The trigger mechanism serves to channel the flow of compressed air to shift this balance.

For example let's say a movable valve plunger (a) sits above the piston head (b). When the trigger is in the released position, compressed air can flow to both sides of the valve plunger. It flows directly through the air reservoir to a lip around the bottom of the plunger, through the trigger valve (c) and a small plastic tube (d) until it reaches the area above the plunger. Since compressed air flows to both sides of the plunger, air pressure balances out. But the plunger is also attached to a spring (e), which pushes it downward. This shifts the pressure balance: When the trigger is released, there is always greater pressure above the plunger than below it.

Some nail guns can launch nails at 1,400 feet per second. Learn all about pneumatic and combustion nailers.
Photo courtesy Hitachi Power Tools

This imbalance keeps the plunger pressed against the seal surrounding the piston head. With the plunger in this position, the compressed air flowing into the gun can't reach the top of the piston to push it down.

Here's what happens when you pull the trigger on a pneumatic nail gun:

The trigger valve closes and opens a passageway to the atmosphere. With the trigger valve in this position, the compressed air can't flow to the area above the valve plunger.
There is greater pressure below the plunger than above it. The plunger rises up, and the compressed air makes its way to the piston head.
The compressed air drives the piston and the blade downward, propelling the nail out of the chamber.
As the piston slides downward, it drives the air inside the cylinder through a series of holes, into a return air chamber (f).

As more air is pushed into the chamber, the pressure level rises. When you release the trigger, compressed air pushes the plunger back into place, blocking the air flow to the piston head. With no downward pressure, the compressed air in the return air chamber can push the piston head back up. The air above the piston head is forced out of the gun, into the atmosphere.

Pneumatic nail guns work very well, even at driving thick nails through hard material. But they are somewhat cumbersome tools: You need to drag around a bulky air compressor to power one. In the next section, we'll look at a high-powered nail gun design that doesn't need an external power source.

Check out the next page to learn about combustion nail guns.

Combustion Nail Guns

One of the newest nail gun machines to hit the market is the combustion nailer. These portable guns generate hammering power with internal combustion, the same force that keeps your car going (see How Car Engines Work).

At the most basic level, combustion guns are a lot like pneumatic nailers. They have a long blade attached to a sliding piston, which is moved by an imbalance in atmospheric pressure. The piston moves downward when there is greater pressure above it, and it moves upward when there is greater pressure below it.

The difference between pneumatics and combustion models is the source of the pressure imbalance. Just like your car, combustion guns have a reservoir filled with a flammable gas. An electronic control mechanism releases a little of this gas into a combustion chamber just above the piston head. A small fan in the combustion chamber vaporizes the gas, mixing it up with the air particles.

This design has a double trigger mechanism. To hammer a nail, you need to pull down the trigger and press the barrel up against the surface at the same time. Pressing the barrel down pushes back a metal valve around the main cylinder. This controls the gas intake and exhaust cycle of the gun.

Here's what happens when you activate both triggers:

The valve piece (shown in green) slides back around the cylinder. As it moves back, the valve closes the exhaust port at the top of the gun. As it keeps moving back, it briefly opens the intake port from the gas supply (shown in blue), and then closes it again. This lets a small amount of gas inside, which the fan mixes with the air.
The gun's battery sends a charge to a spark plug at the top of the combustion chamber. This ignites the gas, causing a small explosion.
The pressure of the explosion propels the piston downward, driving the blade into the nail so that the nail is shot from the gun. As the piston pushes downward, it compresses the air in the cylinder.
When you lift the gun off the nailing surface, the valve slides back down. This opens the exhaust port, so the exhaust can escape.
The compressed air in the return chamber pushes the piston back up, to the "ready" position. Essentially, the air in the return chamber acts like a spring.

The second trigger in this gun is intended as a safety device: you have to pull the trigger and press the gun against a surface to shoot a nail. As we'll see in the next section, this mechanism helps prevent some nail gun injuries, but it may lead to other sorts of accidents.

Nail Gun Safety

In the last section, we saw that a combustion nail gun has two separate firing triggers. Most modern nail guns are built with similar safety catch devices, to keep people from accidentally shooting nails through the air. In the diagram below, you can see how a simple safety mechanism might work in an electric nail gun. The gun has a catch that holds the blade in place. To release the catch, you have to press the gun against something.

This sort of device may reduce the risk of certain injuries, but it is not a foolproof system. With this type of gun, carpenters tend to keep the main trigger depressed at all times, using the safety catch as the actual triggering mechanism: When they press the gun down on a surface, it automatically drives a nail in.

When you use the gun this way, it's a lot easier to accidentally fire a nail. All you have to do is press the gun barrel against your leg or bump into someone with it. Every year, hundreds of people are rushed to the emergency room with these sorts of injuries. To reduce this risk, some manufacturers build a sequential trip system into their guns. In this type of nailer, you have to release and depress the trigger every time you want to fire a nail.

No matter how a gun is designed, it should be appreciated for what it is: an extremely powerful, dangerous machine. Just like a handgun, power nailers fire projectiles at high speed -- some designs launch nails at speeds reaching 1,400 feet per second (427 meters per second).

In this case, convenience definitely comes at a price. Fumbling with a power nail gun might put you intensive care, while the worst you can expect from your old hammer is a bruised thumb.

For more information on nail guns and related topics, check out the links on the next page.