Rotary Hammer vs Hammer Drill | Looking Inside

Using Hammer Drills VS Rotary Hammers

So you’ve got some holes to drill. In concrete. Well, that changes things. Sure, you might be able to get by with a regular drill and a masonry bit, but then again you might not. It depends on how hard the concrete is, how much aggregate is in the mix, and how many holes you have to drill. Then you have the strength of your cordless drill. You may need a drill designed specifically for drilling into concrete. Two tools fit the bill. Knowing the differences between the rotary hammer vs hammer drill question helps you pick the right tool for the job.

What is a Rotary Hammer?

A rotary hammer engages in several actions simultaneously. It both drives the bit forward into the material being drilled while also turning the bit much like a drill. A piston system and air pressure drive the bit into the concrete or masonry material. This combination bits much more strongly than a hammer drill. There are also fewer actual strikes.

The rotary hammer uses either SDS-Plus or SDS-Max bits. Hilti has alternate names for these, but they’re fully compatible. These bits slide and lock into the rotary hammer chuck and don’t require a chuck key or any other tool to insert or remove. You can also find spline bits, but they are much less common and more or less obsolete.

A rotary hammer usually dwarfs a hammer drill in size and the shape doesn’t really resemble a typical drill. You also never use a rotary hammer to drive fasteners, whereas a hammer drill can do double duty.

The Rotary Hammer Mechanism

The reason rotary hammers drill so much faster than a hammer drill comes courtesy of their robust internals. While a hammer drill “vibrates” its way into the surface, a rotary hammer pounds away with a whole lot more force.

Rotary hammers use a drive piston that exerts air pressure to a flying piston. That drives the bit forward quickly even as the electric motor spins the bit rotationally. The best rotary hammers use advanced timing to synchronize the impacts and rotation for even better performance.

rotary hammer internals vs hammer drill
Regardless of whether corded electric or cordless battery-powered, rotary hammers pretty much all work in the same way.

Most rotary hammers feature various modes. Most offer a rotary-only mode that disables the hammering piston action. Others feature this plus a hammer-only mode that effectively turns the tool into a small chipping tool. This often comes in handy when removing small amounts of brick, block, or stone. It also works well for removing linoleum or tile.

Metabo KHE 3250 rotary hammer mode switch

What is a Hammer Drill?

A hammer drill is simply a type of drill. Where a regular drill rotates the bit to drill into concrete or masonry material, a hammer drill adds a percussive action. A pair of impact gears fit together such that when the bit rotates in hammering mode, they produce almost a vibration against each other. This occurs at a very high rate due to the number of ridges along the circumference of the gears. It’s not uncommon to see over 20,000 IPM, or impacts per minute.

hammer drill mechanism.gif
Image courtesy of Zhejiang Hangbo Powertools Co.

This small vibration effect gets transferred to the bit along its axis by the motion of the chuck. The result is a bit that drills rotationally while slightly hammering into the material as it drills. The effect is subtle, but it really does improve upon the use of a simple drill equipped with a masonry bit.

Editor’s Note: See our hammer drill vs drill article for more info

You may notice that a hammer drill doesn’t go into hammer mode until you press it into the material. This is by design. A set of springs serves as a clutch to separate the two ridged discs. When you push the bit into the concrete, they come together, activating the mechanism.

hammer drill clutch and modes

Most hammer drills, and certainly all cordless hammer drills have a switch to put the tool into a drill-only mode. This disengages the hammering mechanism, letting you use the tool for wood drilling and fastening tasks that don’t need the hammering action.

How Do Hammer Drill Impacts Compare to Rotary Hammer Impacts?

Compared to the hammer drill, a rotary hammer creates impacts of much greater force. In essence, a hammer drill relies on the user to press into the material to create a greater amount of impact force as it drills. The rotary hammer physically forces the bit into the material via the flying piston once activated.

You can think of a hammer drill as “vibrating” against the concrete to loosen it up. Conversely, a rotary hammer actually chips away at concrete while it drills.

dewalt flexvolt advantage hammer drill

Rotary Hammer vs Hammer Drill Maximum Hole Sizes

Whereas hammer drills stop being practical at holes around 1/2-inch in size, a rotary hammer can drill holes as large as 2″ in diameter. Even when used on smaller holes, a rotary hammer drills much more quickly into concrete than a hammer drill with the same-sized bit.

Read our how a rotary hammer works article if you want to know more about the specific mechanism in greater detail.

Using Hammer Drills VS Rotary Hammers
The rotary hammer means business.

Hammer drills function as “part-time” concrete drilling tools. You don’t want to use these tools full-time for drilling lots of holes. They simply don’t do the job well—and rotary hammers have become quite affordable. That also plays into the size of holes you want to drill with these tools.

For 1/8″ up to 1/4″ holes, a hammer drill should serve you well unless you plan on drilling dozens of them. Over 1/4″ and we really prefer the speed and flexibility of a rotary hammer. Even the added weight (these tools typically outweigh their hammer drill counterparts) is more than made up for by the faster drilling speeds.

Large Jobs, Small Jobs

I don’t know what you consider a “large” job, but for us, it’s anything requiring more than a dozen holes or enough holes over a certain size. A smaller hammer drill works great for that light-duty work. A mason or tradesman who needs to drill 3/8-inch or larger diameter holes in masonry, drill through rebar, or break up concrete will reach for that rotary hammer.

So who uses hammer drills? Everyone who loves the way these tools provide an added feature for almost no added cost. That includes DIYers, carpenters, plumbers, MRO (maintenance, repair, operations) professionals, and HVAC technicians.

DeWalt 60V Max SDS-Max FlexVolt 1-3/4" rotary hammer DCH614

We love hammer drills for tackling 1/4-inch or smaller holes for periodic Tapcon installation. Hammer drills typically cost less than rotary hammers. It can be used for wood or masonry as well. The rotary hammer only does one or two things: drill in concrete and possibly function as a basic chiseling tool. Where you might find a hammer drill knocked off course by heavy aggregate, a rotary hammer will drill steadily through concrete.

Rotary Hammer Bits vs Hammer Drill Bits

The nature and types of rotary hammer bits allow for a greater concentration of carbide and a more aggressive flute pattern for faster chip removal. Take a look at these larger SDS-Max bits:

Diablo rebar demon SDS-Max Plus bits

Hammer drill bits often look very similar to regular drill bits with a small bit of carbide at the tip. They do have the added advantage of supporting a thicker core with shallower flutes. Check out these Bosch Bluegranite bits as an example:

Bosch BlueGranite Turbo Carbide Hammer Drill Bits
Bosch BlueGranite Turbo Carbide Hammer Drill Bits

Wrapping it Up

To wrap it up—for smaller, easier concrete holes, the hammer drill is the better choice. Rotary hammers get the harder jobs done more quickly and with more power. They also have a much wider and more versatile bit selection. When comparing a rotary hammer vs hammer drill take all this into consideration before you buy.

If you’re a Pro, and you have any tips about using hammer drills vs rotary hammers, add them in the comments below. Happy drilling!

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