So you have some holes to drill. in concrete. Well, this changes everything. Sure, you might be able to get around with a regular drill and a masonry bit, but you probably still can't. This depends on the hardness of the concrete, the aggregate content of the mix, and the number of holes that need to be drilled. Then you have the power of a cordless drill. You may need a drill bit specially designed for drilling holes in concrete. There are two tools that can meet the requirement. Knowing the difference between a rotary hammer and an impact drill can help you choose the right tool for the job.
What is a rotary hammer?
The electric hammer performs multiple actions at the same time. It both advances the drill bit into the material it is drilling, while also turning it like a drill. A piston system and air pressure drive the bit into the concrete or masonry material. This combination drill is much stronger than a hammer drill. There are also fewer actual strikes.
Hammers use SDS-Plus or SDS-Max bits. Hilti has alternate names for these, but they are fully compatible. These bits slide and lock into the rotary hammer chuck and do not require a chuck key or any other tools for insertion or removal. You can also find spline bits, but they are less common and more or less obsolete.
Rotary hammers are often dwarfed in size and not shaped like a typical power drill. You also should never use a rotary hammer to drive fasteners, a hammer drill can do double duty.
rotary hammer mechanism
The reason a rotary hammer drills much faster than a hammer drill is due to its robust internal construction. As the hammer drill "vibrates" into the surface, the rotary hammer strikes with greater force.
Rotary hammers use a drive piston that applies air pressure to a flying piston. Even as the motor spins the bit, it drives the bit forward quickly. The best rotary hammers use advanced timing to synchronize impact and rotation for better performance.
Most rotary hammers have multiple modes. Most offer a spin-only mode, which disables the hammering piston action. Others have this feature along with a hammer-only mode that effectively turns the tool into a small cutting tool. This often comes in handy when removing small amounts of bricks, blocks or stones. It's also great for removing linoleum or tile.
What is a Hammer Drill?
A hammer drill is just a drill bit. Where a normal drill rotates the bit to drill into concrete or masonry material, a hammer drill adds percussion action. A pair of impact gears fit together so that they almost vibrate against each other as the bit rotates in hammering mode. This happens very frequently due to the number of ridges along the circumference of the gear. It is not uncommon to see over 20,000 IPM or impacts per minute.
This tiny vibration effect is transmitted to the drill bit by the movement of the chuck along its axis. The result is a drill that spins to drill a hole while gently hammering into the material as it drills. The effect is subtle, but it does improve using a simple drill equipped with a masonry bit.
Editor's Note: For more information, see our Hammer Drills & Bits article
You may notice that the hammer drill doesn't go into hammering mode until it's pressed into the material. This is by design. A set of springs acts as a clutch that separates the two ridged discs. When you push the bits into the concrete, they come together, activating the mechanism.
Most impact drills, and of course all cordless impact drills, have a switch that puts the tool in drill-only mode. This disengages the hammering mechanism, allowing you to use the tool for wood drilling and fastening tasks that don't require hammering action.
How does a rotary hammer impact compare to a rotary hammer impact?
A rotary hammer produces a much stronger impact than a hammer drill. Essentially, hammer drills rely on the user to press into the material to create more impact while drilling. Once activated, the rotary hammer physically presses the bit into the material via a flying piston.
You can think of a hammer drill as "vibrating" the concrete to loosen it. Instead, a rotary hammer actually chops up the concrete as it drills.
Rotary Hammer and Hammer Drill Maximum Hole Diameter
While hammer drills are no longer practical in holes as small as 1/2 inch, rotary hammers can drill holes as large as 2 inches in diameter. Even when used on smaller holes, a rotary hammer drills into concrete much faster than a rotary hammer drill with the same size bit.
If you want to learn more about a specific mechanism, read our How Rotary Hammers Work article.
Hammer drills are used as "part-time" concrete drilling tools. You don't want to use these tools full time to drill a lot of holes. They simply don't do the job right – and rotary hammers have gotten pretty affordable. This also affects the size of the holes you want to drill with these tools.
For 1/8" to 1/4" holes, a hammer drill should work fine for you, unless you plan to drill dozens of them. Over 1/4" we really prefer the speed and flexibility of the rotary hammer. Even the added weight (these tools often exceed their hammer drill counterparts) is more than made up for by the faster drilling speed.
big job, small job
I don't know what you consider a "big" job, but to us it means anything that requires more than a punch hole or enough holes over a certain size. Smaller impact drills are great for this kind of light work. A mason or craftsman who needs to drill holes 3/8 inch or larger in masonry, drill through rebar, or break concrete will reach for a rotary hammer.
So who uses a rotary hammer? Everyone who likes these tools can provide additional features at almost no additional cost. This includes DIYers, carpenters, plumbers, MRO (maintenance, repair, operations) professionals and HVAC technicians.
We like hammer drills for holes 1/4" or smaller for regular Tapcon installations. Hammer drills generally cost less than rotary hammers. It can also be used on wood or masonry. A rotary hammer can only do one or two things: drill holes in concrete and possibly serve as a basic chiseling tool. Where you might find the hammer drill knocked over by heavy aggregate, the rotary hammer will drill steadily through the concrete.
The nature and type of hammer drill bits allow for a higher concentration of carbides and a more aggressive flute pattern for faster chip removal. Check out these larger SDS-Max drills:
Hammer drill bits generally look very similar to regular drill bits with a small amount of carbide at the tip. They do have the added advantage of supporting thicker cores with shallower grooves. Take these Bosch Bluegranite drill bits as an example:
to sum up
All in all – for smaller, easier concrete holes, a percussion drill is the better choice. Rotary hammers are faster and more powerful for tougher jobs. They also have a wider, more versatile selection of drill bits. When comparing rotary hammer vs hammer drill, consider all of these factors before buying.
If you are a pro and you have any tips for using an impact drill vs rotary hammer, please add them in the comments below. Happy drilling!