Hammer drills and rotary hammers

Concrete Construction, Oct, 2004

Every application has its tool, and every tool has its application. This statement is particularly true in the world of power tools, especially with respect to hammer drills and rotary hammers. These two tools are often mistaken for one another, and it's not hard to see why--they look so much alike.

What immediately sets them apart is price. At first glance, a $150 hammer drill (with 3/4-inch-diameter hole capacity) seems preferable to a $225 rotary hammer with a 7/8-inch hole capacity. The hammer drill has more amps, and the rpm on each tool's two-speed motor are nearly the same. So why would you ever buy the more expensive rotary hammer?

But buyers who opt for the less expensive tool are later upset when their hammer drills, particularly the cordless variety, fail to live up to expectations.

Tom Fogarty, sales service product trainer with Bosch Power Tools and Accessories, stresses that it is important to know the application before buying the tool. What material are you drilling? What is the diameter of the hole you are drilling? And, how many holes do you plan to drill?

While the cheaper hammer drill might seem like the perfect versatile tool, it isn't. And the rotary hammer that seems like an expensive, exclusive tool for only a few occasions, often isn't. Essentially, the hammer drill is 80% drill and 20% hammer, while the rotary hammer is 20% drill and 80% hammer, Fogarty says.

The hammer drill, with its ratchet-like impact mechanism, works best on brick, block, and light concrete, but not hard concrete (that is, high compressive strength concrete or that with large aggregate). It will work on hard concrete, but since it requires the operator to apply pressure to make it work, it can offer only a fraction of the rotary hammer's impact and is simply less efficient.

Not so for the rotary hammer, which has an inline electro-pneumatic impact mechanism that applies the same force each and every time. In fact, leaning on the rotary hammer actually decreases its effectiveness.

So if you plan to do a few holes at a time, for say anchoring, the less expensive hammer drill is probably the way to go. If, however, you are making dozens of holes, the repetitive pressure needed for a hammer drill will tire you out, and drilling will take longer. The rotary hammer's impact mechanism needs no extra pressure, so not only will the holes go more quickly, but it will be less tiring to operate.

The latest trend has been the development of cordless tools. Manufacturers are locked into a "space-race" for the development of new and better battery technologies, each one trying to create a cordless tool that will replicate the unlimited power of plug-in tools. Unfortunately, that has not happened yet. The next big development will probably be the use of lithium ion batteries.

Consequently, cordless tools have become almost a consumable commodity. According to Fogarty, the typical cordless tool can last from one to three years depending on how it is used, while the corded variety can last much longer. Some contractors have been known to replace their tools yearly based on the various levels of use and abuse they have inflicted upon them--including dropping and improper charging techniques. While batteries are each tool's life source, manufacturers continue to strive for longer run times and more durability.

Convenience makes the cordless tool more desirable than corded tools. The absence of long cords and the ease of getting the tool into tight or awkward places are what make cordless tools so valuable. Tripping hazards, the hassle of stringing the cord through the skeleton of the building, moving the generator to get the tool to reach the needed position, or getting tangled in the cords--all are eliminated with the cordless tool.

Cordless tools have found a niche in the construction trade, but that doesn't mean toolmakers will stop making corded tools, says Fogarty. Chances are contractors will have both kinds in the shop. And just like cordless tools, they may have both hammer drills and rotary hammers. Knowing when to use which tool will help contractors get the most out of their tool investment.

The following is a group of cordless hammer drill/drivers and rotary hammers to consider. If you would like to learn more about any of the tools, circle the reader service number and mail in the card.

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