Pop quiz, hotshot: what are the major differences between an impact driver and hammer drill? If you’re stumped, you’re not alone. The answer: mechanisms and applications. Let’s drill down to the impact driver vs hammer drill question right now.
- Impact drivers apply rotational impacts with a hammer and anvil mechanism
- Hammer drills apply forward impacts with a tooth and bearing or ridged disc system
- Impact drivers are the right tool for driving screws and other fasteners
- Hammer drills are the right tool for making holes in masonry
- For bigger fasteners, you move from an impact driver to an impact wrench
- For bigger holes in concrete switch your hammer drill out for a rotary hammer
Impact Driver vs Hammer Drill Mechanisms
Impact Driver Mechanism
A hammer and anvil design helps impact drivers accomplish their tasks. Most impacts have two hammers although some have three. As the tool’s motor turns a spring-loaded hammer plate, the spring compresses and the hammer and anvil plates push apart. For a fraction of a second, there is space between the plates and potential energy in the spring.
In this space, the hammer and anvil plates slip past one another only to slam together again forcefully by the spring’s kinetic energy. This creates a great deal of torque (and a little downward force) as the hammers hit the anvils and transfer the energy through the bit to turn the fastener. The impact driver repeats this process rapidly. We look to the tool’s impacts per minute (IPM) or blows per minute (BPM) for a measure of impact rate in numbers that get as high as 4000 IPM in an 18V impact driver.
Hammer Drill Mechanism
To an extent, the hammer drill’s mechanism is a difference of degree rather than kind. But the difference results in forward force and less torque than an impact driver.
The hammer drill also uses two plates but trades out the hammer and anvil design a mechanism that looks like the way two checkers stack together (king me!).
There are some other excellent images here.
As you start to drill, the teeth slip up and over the opposite teeth or bearings to create a motion that pushes forward and slips back. This transfers through the bit into a chipping function while the plates, interlocking for a fraction of a second before separating apart again, quickly turn the bit.
It’s common for the impact rate of a hammer drill to be tens of thousands of BPM (point of preference—we prefer IPM for impact drivers and BPM for hammer drills, though some manufacturers differ). Some easily exceed 30,000 BPM.
Impact Driver vs Hammer Drill Applications
Impact Driver Applications
The impact driver’s mechanism creates rotational impacts that are excellent for driving screws of all kinds and hex bolts. The impulsing torque can drive and remove tough fasteners when the static torque of a drill would cause it to cam out or simply stop altogether.
You can also use an impact driver to drill with a hex shank bit but it’s not optimal. The form factor of the stubby impact driver differs enough from a hammer drill (which looks like a regular drill/driver) that you can easily tell the difference.
When you reach the limits of an impact driver, you step up to an impact wrench.
Hammer Drill Applications
Hammer drills are the right tool for drilling into masonry (brick, stone, block, concrete) to set anchors and create holes for outlet boxes. With a masonry bit, the hammer drill chips as it turns to push through the material. It’s more compact and lightweight design compared to a rotary hammer makes it a good choice for drilling holes up to 1/2″ or so in masonry, but it doesn’t include dust collection to keep you from breathing in silica dust.
A traditional hammer drill is not the right tool for driving screws. As we just mentioned, hammer drills often look just like a traditional drill. However, most modern cordless hammer drills let you select between drill, drive, and hammer drill modes so you can do all three functions with one tool.
Upgrading Your Hammer Drill to a Rotary Hammer
When you get to the limit of a hammer drill, it’s time to step up to a rotary hammer. People sometimes confuse a hammer drill and a rotary hammer, even using the name to rotary hammer drill. It’s true that a rotary hammer is also for masonry, but it is larger, used for bigger work, and employs a different mechanism: a piston and air pressure. More on that in a future article!
We hope you’ve benefitted from our impact driver vs hammer drill crash course. Feel free to toss any questions our way in the comments below and we’ll do our best to help you out!
Like the hammer drill featured in this article? It’s the Makita XPH07!