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.

Photo courtesy Hitachi Power Tools There are a wide range of nail guns on the market today. Different designs are configured for specific nail sizes and applications. See more pictures of power & work tools.

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. You can see how this sort of gun works in the animation below:

In this design, the motor (powered by a battery or household AC current) rotates two drive axles. The front axle moves a small scooper plate (a), a metal disc with a curved groove cut into it, and the rear axle moves a gear train, which turns a small triangular metal cam (b). Here's what happens when when you pull the trigger:

1. The triangular cam turns, pushing down one end of a lever (c).
2. The lever pivots, pushing up on the hammer (d). As the hammer pushes up, it compresses two springs (e).
3. 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.
4. As the scooper plate turns, it lifts the hammer higher and finally releases it.
5. The two compressed springs drive the hammer downward at high speed. If a nail is in position, the hammer launches it from the gun.

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.

Photo courtesy Hitachi Power Tools A standard nail gun magazine: A spring pushes the nails up into the feed mechanism, which sets it up in front of the blade.

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:

1. The electrical circuit runs the current through the electromagnet so that the piston extends downward. Typically, the piston is attached to a sturdy blade.
2. The blade makes contact with the nail, forcing it out of the gun.
3. At the bottom of the cylinder, the piston hits an electrical switch.
4. 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.

 

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