What’s an Impact Driver, and How Does It Work?

It’s time to talk about the most versatile tool that you can add to your collection.

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What’s an Impact Driver, and How Does It Work? © What’s an Impact Driver, and How Does It Work?

Few of the power tools in my collection deserve higher praise than my impact driver. It’s a Hercules impact driver from Harbor Freight, and I've used and abused it for countless projects since acquiring it second-hand a few years ago. It has yet to let me down, and its versatility is to thank for keeping me sane in far more situations than I care to remember.

Its usefulness comes down to its function. Impact drivers are a little more tool than a fancy drill and a little less tool than an impact wrench. Today, The Drive’s top tool nuts will break down exactly what that means by exploring what an impact driver is, what it’s used for, and why it became one of my go-to tools.

Hank O'Hop

What Is an Impact Driver?

To understand impact drivers, you must first understand the purpose and functionality of drills.  

One of the primary purposes of a drill is to drive fasteners into materials. The use of rotational force provided by the motor and the pressure you supply with your hand makes this possible. Pretty simple, right? But what if the material is dense and tough to drill into? What if you hit a knot or a hard spot in the wood while you drill? Or what if a long faster has too much drag? You might think to simply try different speeds and pressure levels, but that's not always enough.

An impact driver is designed to solve exactly these types of problems with a two-pronged attack. Impact drivers use motors that supply more significant levels of torque than a drill and they use an impact action that helps to drive fasteners through more rigid materials when under load.

If that sounds familiar, it’s because that impact action is similar to the function of an impact wrench and a hammer drill. In comparison, impact drivers aren’t as powerful as impact wrenches and hammer drills, nor are they as precision friendly as a power drill. However true that may be, the result of the design is a tool that lands somewhere in the middle of all three. You wind up with a tool that can be used in various settings with a compact size that compliments all projects.

Here we can see the impact mechanism between the motor and the collet. , Hank O'Hop

How an Impact Driver Works

The power created by an impact driver might seem like a minor miracle, but these helpful tools rely on reasonably simplistic mechanisms. The internals looks very much the same as a drill in that you have a motor that applies rotational force. Only it’s more compact to allow room for the hammer and anvil.

Just like with a drill, there’s an output shaft. Only before the output shaft reaches the chuck or collet, in this case, there’s an additional mechanism that’s composed of a spring-driven hammer and anvil.

A closer shot of the spring and hammer that supply impact. , Hank O'Hop

Until enough load is applied, the spring forces the hammer against the anvil, which allows it to act just like a drill. The magic happens once the fastener provides enough opposition.

The hammer can cam away from the anvil and depress the spring when the system is under load. After it clears the anvil, it snaps back into position and spins freely until it strikes the anvil again. The collision of the hammer against the anvil creates the impact action. That impact supplies the force for the system to continue to drive a fastener into place.

Here we can see the anvils that the hammers strike to supply the impact action., Hank O'Hop

This system replicates the action of striking a wrench with a hammer just on a much smaller scale.

Why Is the Impact Necessary?

The impact function is crucial for driving fasteners through hard materials, but that’s not the only time it comes in handy.

Say you’re driving fasters in a tight spot that you can’t get a drill in, nor can you apply much pressure because you’re at an awkward angle. The impacting action helps to drive the faster through whatever you need it to. It also delivers a shock that helps to free stubborn fasteners that a drill will struggle with.

You may be able to use a normal drill for either setting, but you can run into several issues. As we already said, applying too much force bogs down the motor and can ultimately kill your drill. Not only that, but the increased pressure is also hard on your wrists, which is never a good thing during a long day of wrenching.

What Makes Impact Drivers So Versatile?

The impact action and rotational force created by impact drivers allow the tool to be used for many things. But perhaps what truly boosts its versatility is that quick-change drive attached to the head.

Most impact drivers feature a quick-change collet that accepts bits that feature a 1/4-inch hexagonal shank. Drill bits, bit drivers, and all sorts of other goodies can hook right into this slot, allowing you to get to work on anything. Heck, you can even get a keyed-chuck with a 1/4-inch shank that will enable you to use standard drill bits in there. Again, it’s not as precise as a regular drill, but it comes in handy when you need to quickly put a hole in something.

Beyond that, possibly its most helpful feature is that it works with socket adapters that essentially turn your impact driver into a mini-impact wrench. Factor that in with everything else, and you can see why an impact driver comes in handy for virtually any project around the shop.

Impact Wrench on the left, impact driver on the right. Choose your fighter., Jonathon Klein

Impact Drivers vs. Impact Wrenches 

Before we get ahead of ourselves, we should explain the differences between an impact driver and an actual impact wrench.

The most significant factor is that an impact wrench is a dedicated tool that features a permanently mounted ¼-inch, 3/8-inch, or 1/2-inch socket drive. And because impact wrenches are explicitly intended for dealing with stubborn nuts and bolts, they’re generally far more powerful than impact drivers. 

Because of this, an impact driver does not take the place of an impact wrench. The 1/2-inch socket adapter available for your impact driver will likely see little to no use because they generally don’t provide enough power to break large hardware free.

Again, size says it all. Here we have a side-by-side comparison of the striking mechanisms used to generate impact. , Hank O'Hop

Again, the primary purpose of an impact driver is to drive fasteners through harder materials. Being able to free nuts and bolts is something of a byproduct.

Can I Use an Impact Driver on My Car? 

Yes, you can use an impact driver on your car. They really can't compare to even a compact impact wrench when it comes to dealing with nuts and bolts, but they're a decent compromise in many situations. Though not exactly intended for it, I personally use socket drive adapters for dealing with smaller fasteners in many situations. I'm sure many others have done the same.

Mjolnir, we mean a Milwaukee Impact Wrench. , Jonathon Klein

Furthermore, the ability to use one as a drill makes them an excellent choice for driving sheet metal screws and other miscellaneous tasks. Again, a drill is superior when precision is of utmost importance. However, the lightweight and compact design of impact drivers paired with higher torque output make them perfect for a variety of automotive-related tasks.

In short, an impact driver isn’t the perfect tool for every job, but its versatility makes it a great addition to any mechanic’s tool collection.

Video on Impact Drivers

We’re always on your side, and we get that most of you are visual learners. Not only that, it can be tough to put the exact workings of these tools into perspective without visual aid. This video not only provides a breakdown of an impact driver but does a great job at explaining how they all work together!

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