How Are Hammer Drills Different Than Rotary Hammers?
Are hammer drills different than rotary hammers? That’s the question we tackle in this edition of Training the Apprentice.
You aren’t the first person to wonder this, and you won’t be the last. For someone new to these tools of the trade, it’s a fair question. After all, both tools seem to function similarly, they don’t look wildly different from one another, and they both have “hammer” in their name.
Well, I don’t mean to kill the suspense for you, but yes, they are different tools. To be fair, there are definite similarities between the two. But, there are also a few key differences that often shift them each to different applications. In a previous article, we explained how to choose between a hammer drill and a rotary hammer for concrete drilling. We quickly mentioned how the mechanisms differ, and we touched on the applications each tool focuses on.
Well, this question still comes up a lot around here, so maybe it’s worth diving back into. At the risk of being redundant, we thought we’d take a look at both tools and try to explain the difference further.
How Are Hammer Drills Different than Rotary Hammers?
A hammer drill often looks like a traditional drill. That’s because, except for one notable function, it basically is a traditional drill. However, in addition to the standard drill’s normal spinning action, the hammer drill adds, well, some sweet hammering action as well. It uses two ridged, interlocking discs to apply a pounding force to the spinning drill. As the two discs move against each other, the ridges ride up and down, essentially creating a hammer and anvil effect inside the hammer drill. This causes the chuck to move back and forth, which provides a short, rapid hammering action to the bit.
As opposed to an impact driver, which hammers rotationally to add torque to fastening applications, the hammer drill’s pounding force is directed to the tip of the drill bit. The hammering allows the tip of the bit to pulverize the masonry as the bit spins and removes the dust.
Hammer drills work great for drilling smaller holes in porous concrete and masonry. The operative words here are “drilling smaller holes”. This is because you probably shouldn’t use the hammer drill for fastening, but strictly for drilling into stone. Of course, most modern cordless hammer drills have hammerless modes which allow them to work in a more traditional fashion in wood drilling and fastening applications. For instance, the Hilti SF 6H-A22 has dual settings that allow it to be used in multiple applications.
But, the hammering feature is generally intended for drilling small holes in concrete. And, for drilling holes bigger than around 3/8″, you’re probably going to want to switch to a rotary hammer.
The Bigger Guns
A rotary hammer often doesn’t look like a traditional drill. It creates a pounding force in addition to torque like the hammer drill, but the force is created by air pushing a piston down. Imagine the pistons in a car engine. The piston is driven away from the top dead center by an expanding air column only to return to top dead center and be driven away again by another expansion. This has the same effect as the discs of a hammer drill, but it generates much more force. You might also notice a rat-a-tat-a-tat sound as the piston does its work.
In addition, rotary hammers use a different chuck than hammer drills. Hammer drills typically use a standard, adjustable chuck. Rotary hammers use a spring-loaded, SDS chuck that requires special SDS bits.
Because it’s more powerful than a hammer drill, a rotary hammer is used for heavy-duty, dense concrete. It can drill bigger holes, and rotary hammers typically have a “hammer only” mode, allowing them to function as a sort of mini jackhammer. Because of their versatility, rotary hammers not only drill but also break up concrete and clay along with removing tile. Incidentally, be sure to check out our How To Remove Tile article.
So, are hammer drills different than rotary hammers? Yes, but they have similar functions. The differences between them revolve around the inner mechanism that drives the hammering action, their respective chucks, the amount of hammering force they produce, the size of the job, and the applications they can tackle. To reiterate, if you’re drilling smaller diameter holes in concrete, the hammer drill might be your best friend. If you need larger diameter holes, or if you need to demolish something, look to the rotary hammer.