How Does an Impact Driver Work?

how impact driver works

Last Updated on July 11, 2023

From time to time we still run across folks who don’t quite understand how an impact driver works. Impact drivers are an essential tool for any Pro. They let you apply more force (or torque) than a drill. Used in tandem, a cordless drill handles hole-making while an impact driver sets or sinks the fasteners. For basic screwdriving, an impact driver might be the only tool you need. If you have ever wondered how an impact driver works, this article should help answer your questions.

How an Impact Driver Works Internally

First of all, check out our impact driver vs drill article if you want an overview of the difference between these two tools. We don’t want to rehash that here. Instead, we want to go over how exactly an impact driver works internally to generate its impressive torque.

Constant Pressure vs Impacts

A regular drill applies static rotational force to the shaft and, consequently, the bit. In other words, it exerts a constant pressure to rotate the chuck. As the job gets more difficult, inertia kicks in. That drill fights the user and wants to exert just as much force on your hand and arm as you are exerting on the bit. If the bot binds, but the tool continues delivering all of its power, you can encounter some serious issues!

Impact drivers rely on something else entirely—and it makes them a truly unique tool. An impact driver creates rotational impact force when you need additional torque. It uses a spring, hammer, and anvil to accomplish this. 

As the motor turns the shaft, the spring compresses and then releases. This forcefully drives the hammer down until it drops into place where it can strike rotationally against the anvil. This action happens very rapidly. In fact, most impact drivers hit more than 50 times every second. This creates much more force than a drill can typically muster in a similarly sized tool.

How an impact driver works 01
Here you can see the hammer (right) and anvils (left) of an impact driver. The spring is hidden underneath the hammer.

Pushing vs Rapid Punching

Here’s another way to think about it: Using a drill is like setting your hands against an object and pushing. Using an impact driver is like punching it rapidly. Think of it like the rapid punching of legendary king fu master IP Man… except less messy. You use the same muscles to create both forces, but the rapid punches deliver much greater force overall. A punch also only impacts the surface for a brief moment while you can engage a push much longer.

Milwaukee impact driver anvil
Notice the rather large anvil that spins and strikes to drive the chuck forward when the driving gets tough.

Where and When an Impact Driver Really Works Well

Just like a punch, the impact mechanism creates a more violent action. That’s why you see many Pros shy away from using impact drivers with twist drill bits and spade bits. While it gets the job done, it’s not nearly as smooth of an experience.

On the other hand, that violence works perfectly for driving screws. An impact driver also tends to drive higher torque fasteners much more quickly than a drill. The speed of the hammer/anvil impact combined with the additional force gives you the ability to drive longer and larger diameter screws or fasteners than you can expect a drill to handle.

How an Impact Driver Provides More Torque

The practical implication of the impact driver mechanism comes down to how it provides torque. Got a long or larger ledger screw or lag bolt? The impact driver makes the best tool for this type of work.

You can drive longer and larger bolts using a standard drill. However, as you get closer to the bottom, the torque requirement increases, making you have to fight to tool for control. Compare that to using an impact driver to drive ledger or lag screws all the way to the bottom using just one hand!

DeWalt vs Milwaukee Impact Driver Review
This task takes much more physical effort (not to mention two hands) with a standard drill driver.

Impact Drivers are Smaller in Size

The icing on the cake is that impact drivers are typically smaller, lighter, and able to get into tighter spaces. The best impact drivers measure less than 5 inches in length! They also won’t wrench violently in a bind-up like a high-torque drill. If that all sounds, well, impactful, you’re not alone. Impact drivers are among the most popular cordless tools on the jobsite.

impact driver vs drill

Knowing how an impact driver works will also help you understand when and where to choose it over a drill. Those are the little tidbits of knowledge that will help as you make the transition from apprentice to seasoned Pro.

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