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How Does an Impact Wrench Work

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When presented with a situation where you need more force and torque than you can get from a standard wrench, an impact wrench is a good alternative. This power tool is especially useful in removing bolts that are too hard to remove with a hand wrench.

Learning how an impact wrench works can be important in defining if you need one for the project at hand.

Using a high amount of torque driven by its hammering action, the best corded impact wrench comes in handy with extracting rusted bolts. Imagine if you set your wrench to a bolt head, and then used a hammer to turn it instead of your hand.

Cordless impact wrenches are also great, and can be used to remove nuts that were overtightened, or to get thick fasteners into difficult material.

There are a few different power sources for impact wrenches, whether pneumatic or electrical. While they all use the same primary action, we will be mainly concerned with how a pneumatic impact wrench works.

An impact wrench with screws and bolts laid on the table

Impact Wrench Construction

There are a few moving parts that give the impact wrench its signature action, but overall it is not very complicated. It is made of the following internal components that work together to create a hammering, twisting force:

  • Rotors to spin the assembly
  • A spring to work the hammer mechanism
  • The hammer, a cylindrical, heavy spinning mass that stores and releases energy
  • The anvil, another cylinder, to twist the shaft and socket
  • A shaft to connect the socket bit to

How an Impact Wrench Works

An impact wrench spins very quickly, and the actions below happen between 2-4 times per rotation. On a wrench spinning at a high RPM (Revolutions Per Minute), this creates a tremendous number of actions.

  1. Pressurized air from the connected air compressor spins vaned rotors, like blowing on a pinwheel at an incredibly high speed.
  2. The spring and hammer assembly start spinning at high speed.
  3. The spring compresses with the spinning action and lifts the hammer above the anvil as it is turning.
  4. At this point, the hammer essentially becomes a flywheel as it spins freely, gathering force through accelerating mass.
  5. There is a groove in the hammer, that when the pieces line up, allows the spring to push the hammer down with the added stored energy of the compressed spring.
  6. The end of the groove in the hammer lines up and strikes the anvil, turning the shaft and connected socket bit.
  7. At this point, the spring compresses again, raising the hammer groove away from the anvil.
  8. The process then repeats.

Different Types of Impact Wrenches

As mentioned previously, there are some different ways that power is provided to the impact wrench. There are also different form factors, some of which come into play when using an impact wrench for larger hardware.

The primary power sources for impact wrenches are pressurized (compressed) air or electricity. Be sure that the impact wrench you pick up uses the power source you want.

Choosing which version works best for your application will depend on the amount of power needed, the location in which you want to use it, and a few other factors.

Pneumatic Impact Wrenches

Compressed air normally provides the most bang for the buck when you already own an air compressor. An air compressor that you connect the wrench to can be used for other tools, and the amount of power provided is very high and very stable.

Close up image of an impact wrench

In addition, it can give you another level of control by adjusting the amount of PSI (Pounds per Square Inch) that is coming out of the compressor.

There are a few drawbacks when using an air compressor to power an impact wrench. The main one is that you will need to have the wrench plugged in with the plastic or rubber hose the entire time you are using it. This can cause problems when trying to move around a lot.

In addition, if there are multiple people using tools plugged into the compressor at the same time, the PSI needed can fluctuate based on what is being used.

Electric Impact Wrenches

With improvements in technology, certain electric power tools have come quite a long way. For manufacturing or jobs using heavy hardware they may not be the best choice, but in a home environment when they are not used very often, they can be a good choice.

The most common (and recommended) electric version of the impact wrench is one that plugs into the wall. This will give you much higher torque for a longer period of time than battery powered impact wrenches.

The main drawback, of course, is that you will need to make sure the cord is long enough to reach where you are working, or that you have a proper extension cord to reach.

Battery powered impact wrenches are also available. Batteries are much more efficient now than they used to be, but they also need to be recharged often. Impact wrenches use a lot of energy with their specialized mechanisms and can run a battery down very quickly.

Impact Wrench Form Factors

While the impact mechanism stays basically the same over the different sizes of impact wrenches that are made, the housing and motor size can have a very large range, from small to big.

Makita impact wrench

The different types of impact wrench housings are listed below from smallest to largest.

  • Inline – used for small jobs, it looks like a cordless screwdriver.
  • Angled drive – this construction pivots in the middle, allowing you to reach tight spaces with a firm grip.
  • Pistol grip – the standard hand drill form factor, usually with a trigger.
  • D handle – used for mid-heavy jobs, these impact wrenches have an enclosed rear grip and one handle on the side, helping to provide leverage.
  • T handle – has a handle on each side forming a “T” shape, as well as a rear grip. These give the best leverage and grip, and are used for the  heaviest of operations.

Impact Wrench Tips

Here are some additional tips for using an impact wrench.

  • Start with lower torque! Excessive torque can break socket bits, bolts, or both.
  • There are normally dials on the impact wrench where you can change the amount of force used. It is better to start at a lower setting.
  • If there is not an adjustment knob on the impact wrench, lower the amount of PSI coming from the air compressor.
  • If you experience low power or torque, check the power source, and/or clean debris and gunk from the anvil.
  • Lubricate the motor and hammer mechanism if necessary.
  • Always use ear and eye protection.
  • Use two hands for stability, even on the lower powered models.
  • Start your bolts by hand and then continue with the impact wrench after you cannot turn the threads any more.

Conclusion

While not necessary for all applications where maybe a little extra elbow grease can do the job, an impact wrench is a great tool for extra stubborn bolts. We do recommend using a hand wrench until you get to the point where the hardware stops responding, or until your hands give out.

With the force being expended in the body of the wrench, the actual torque is not transferred as much to your hands as it is when using, compared to a standard home drill.

Impact wrenches use a fairly unique method of transferring power and torque to the shaft holding the socket bit, and we hope we have been able to enlighten you on how they work.

An expert at home repair, remodel, and DIY projects for nearly 40 years. His first experience came in completely restoring an antique home. Completely redone from the inside out, and restored to its original form, the home is a featured design by renowned Southern California Architect Cliff May, considered to be the father of the California Ranch Home. Now Dennis spends his time on fine woodworking projects and tool comparisons.