Guest blog by Grant Spolander

The invention of the wheel is often credited as a technological turning point for man, but we were drilling holes and fitting things long before we rolled into modern history. Even today, and among the most DIY-challenged of people, you’ll find at least one power tool in each household. And, invariably, it will be an electric drill.

So, it’s not surprising that when I got married some 13 years ago, the first thing I bought for our new home was a power drill. Little did I know that I’d face a barrage of options in the hole-making department.

In the end, I felt I’d made a wise choice, opting for a general-purpose drill that offered class-leading power and the option of variable speed. From past experience, I knew that drilling into different surfaces and materials requires different speeds and different drill-bit pressures; for example, the force and speed that you use to drill steel will differ greatly from how you would drill wood.

I was super-happy with my purchase, and decided one day to hang an entrance gate. The mounting of the gate required a series of holes to be drilled into a vibracrete post. I pulled out my prized power drill, inserted a brand new drill bit, and gave a few customary bursts of the “trigger” so that all of suburbia knew that a man and his drill were about to work.

“Rizzz! Rizzz Rizzz!”

Ummm, what?

“Rizzz! Rizzz Rizzz!”

I tried everything, from moderate force with high speed, to high force with moderate speed, but nothing worked. I stared at the 5 mm deep vibracrete “scar” in disbelief. At this point, my brand new drill bit looked like it had done the rounds at De Beers.

Fortunately, a mate of mine, Rory, was helping me with the job. Rory also happens to run a screen-printing business and spends much of his time mounting high-rise signs, so he’s drilled a hole or two.

I held up my now not-so-prized drill and turned to him for an explanation. Rory had a knowing grin on his face, and was nodding his head in a “Yep, I knew this would happen” fashion. He then pulled out his car keys, walked over to the boot of his car, and took out a blue box with the word “Makita” on it.

He worked in a methodical and noticeably cocksure way, revealing a man-size drill and a strange-looking bit that just dropped into the chuck without having to tighten anything. He lined the Makita up with the hole I was attempting to drill, and with just one hand on the drill and the other in his pocket, he pulled the trigger.

A low-level thumping sound echoed from the wall (a much more appealing noise than the screeching sound my drill had made), and within seconds, the Makita had ploughed through the vibracrete as if it were hot fudge. He then looked at me with a smile on his face and said two words that I’ll never forget: “Rotary Hammer”.

I’m grateful about many things that happened that day, but most of all that my wife hadn’t been around to see how much bigger and better Rory’s drill was than mine…

But, aside from that, a primary lesson was learnt. Nothing beats a Rotary Hammer drill for masonry work.

However, there’s more to the subject of drill selection than just one-upping your mate’s…er… tool size. So, before you rush off and take the Rotary-Hammer plunge, let’s look at how this technology works when compared to “normal” hammer drills. 

ABOVE: You can clearly see how much more “hammering” the Rotary Hammer drill (right pic) uses when drilling into masonry.

LONG IN THE TOOTH

Where to begin? Well, terminology is probably a good place to start, along with the various names used to describe a conventional hammer drill. These include:

  • Percussion drill
  • Impact drill and, of course…
  • Hammer drill

In essence, all these names refer to the same thing: A drill for general use that is designed to drill into both steel and wood, with a selectable “Hammer” option to tackle masonry, too.

The actual percussion effect of a Hammer drill is what makes it very different to a Rotary Hammer drill. Of course, it doesn’t help that both drill types contain the word “hammer”, which leads to confusion around these two technologies. For the sake of clarity, we’ll use the term ‘Impact Drill’ from now on when referring to Hammer Drills.

As mentioned before, most Impact Drills (regardless of brand) use a similar principle to create their percussion effect:  in essence, a design that’s been around for many years, and includes a toothed coupling (or ratchet) that rises and falls with every ridge. The frequency (and intensity) in which this happens is incredibly high, and is largely dependent on the drill’s selected speed, as well as how much force you apply to the drill bit. In other words: more force = more impact. (To a degree, of course).

In contrast, a Rotary Hammer drill uses a completely different setup, which, in many ways, is not that different to what happens in your car’s engine.

CRANK IT UP

Featuring an offset crank mechanism, most Rotary Hammer drills convert a portion of their rotational force into linear force. This linear force is what drives a sealed piston back and forth, pushing a pocket of vacuum-sealed air against a free floating bolt before it.

It’s this bolt that literally hammers the back of the drill bit. This is why Rotary Hammer drills are also referred as electro-pneumatic drills, in that they combine electrical power with pneumatic force. In many respects, this action is a combination of drilling and chipping, both at the same time.

The result? Vastly superior performance when drilling into concrete and masonry.

“But, how much better?” you may ask. That will depend on the “hardness” of the masonry work, but when it comes to high-density concrete and aggregate, there is simply no comparison. It would be like trying to compare a butcher’s knife to a butter knife in the meat-carving department.

However, there are some drawbacks to all this hammer power. For starters, a Rotary Hammer drill is mostly single-purpose in its application. Some people go to great lengths to convert their Rotary Hammer drill into a general-use drilling tool, and although this is technically possible (by fitting an adaptor and 3-jaw chuck), it’s really a misapplication of the drill’s strengths and weaknesses.

ABOVE: The difference between a standard drill bit and a SDS Plus. Needless to say, thanks to its slotted keyway design, the SDS Plus is far less likely to come loose and spin in the chuck. It also requires no tightening and is quick to swop out for another drill bit size.

Strictly speaking, Rotary Hammer drills don’t really have the necessary rotational speed to cover a wide range of drilling applications. What’s more, because of their floating-chuck design, there’s often a lot of free play in the actual movement of the drill, which means that drilling an accurately-sized hole in steel or wood is quite unlikely.

Rotary Hammer drills can also be quite aggressive in how they drill; and, depending on what you’re drilling, using a Rotary Hammer can sometimes feel like you’re swinging a battle axe in a wood-whittling project. This is especially the case in terms of the exit hole, where large chunks of concrete and brick may break away as the drill exits on the other side of the wall. One way around this is to drill a small pilot hole first, and then to drill from both sides of the wall with the final drill size.

However, there are several benefits of using a Rotary Hammer, too, such as the fact that the speed at which a Rotary Hammer will drill into hard surfaces (like concrete) can be up to 10 times faster than the speed of an Impact Drill. And possibly even more.

In addition, given how much impact and knocking force the drill is exposed to, generally speaking, the drill bit quality of a Rotary Hammer (referred to as a SDS PLUS drill bit) is markedly better than that of a conventional tungsten drill bit.

Then, depending on the model you buy, a large number of Rotary Hammers boast a selectable chipping function. This allows you to insert a masonry chisel into the chuck, and to use the drill as a dedicated breaker. However, in terms of use, the intended application here is for light-duty work. Things like chasing a short conduit line, or removing a few tiles in a bathroom or kitchen.

ABOVE: Some Rotary Hammer drills come equipped with a hammer-only function with no rotation. This allows you to use the “drill” as a chipper and light-duty breaker.

Either way, the fact that a Rotary Hammer can be used as a dedicated masonry chisel should give you a good idea about how much more effective the hammer function is on a Rotary Hammer, versus that on a ratcheting Impact Drill.

Interestingly, as mentioned before, most Impact Drills are dependent on the force applied to the drill bit in order to create the impact effect. In contrast, a Rotary Hammer “loses” a lot of its impact force when too much pressure is applied to the drill. This is because the range of motion (of the hammer itself) is reduced when the drill bit is pushed too hard. (One of the reasons why Rory was arrogantly able to drill one handed…)

Lastly, most Rotary Hammer drills feature a built-in clutch mechanism that automatically slips if the drill bit happens to seize in the hole. Should the same thing happen when you’re using an Impact Drill, there’s a pretty good chance that you will crank your wrist, as the rotational force of the seized drill bit gets transferred to the drill itself.

This brings us to our final question: Is a Rotary Hammer drill worth it?

Well… yes and no.

Yes, if you often find yourself drilling into masonry, have a love affair with power tools, and enjoy making your lesser-tooled friends feel inadequate.

No, if you’d rather save money and own a single-purpose drill that ticks multiple boxes. But, in that case, if you’re looking for an all-purpose drilling tool for general DIY work, very few things can beat a cordless drill. But, that’s a whole other story.

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