Take a bite out of concrete

Carbide-tipped drill bits help you get the job done.

by Kay Falk

Carbide-tipped bits are an efficient way for contractors to drill most concrete holes. They provide longer bit life and faster drilling performance compared with steel bits, says Eric Elsmore, senior product manager for masonry drilling at Irwin Industrial Tool Co.

“Carbide-tipped hammer bits use  a grade containing more cobalt. This increases durability, or resistance to fracture. They are designed to pulverize concrete,” he says.

Kurt Honaker, brand manager for Bosch Accessories, adds that the best materials for concrete drilling applications are carbide and diamond. “Steel doesn’t hold an edge like carbide, and carbide is better for impact grinding in demolition work,” he says. “Overall, carbide is the most cost-effective option for everyday concrete drilling because diamond bits are more costly and so are the tools that use them.”

Designs improve
To improve carbide bits, some manufacturers are building a centering point into the tip. “This provides for more accurate hole starting and minimizes walking,” says Richard Lawson, product manager for abrasives and accessories at Metabo Corp. “It also produces a truer round hole.”

Honaker agrees. “Recent advances in the most common shank configuration (see box on page 31), SDS-Plus, include a more pronounced tip that centers the bit accurately at the start of drilling,” he says. “An improved tip design ensures the roundest and smoothest holes possible.”

Elsmore adds, “Another industry focus is to get the dust out of the hole as quickly as possible. This offers longer life because the carbide tip is generally kept cooler and less binding when drilling.”

The flutes, which are the twisting steel channels that swirl up the sides of a bit, run all the way to the tip. “This is what creates less dust buildup in the bottom of the hole,” Honaker says, “which means less overall heat at the tip. These bits will drill faster, smoother and rounder holes.”

Select bits for productivity
In general, the more cutters on a bit, the faster it will cut, although smaller-dimension bits usually come with a standard cutter only.

Our experts suggest keeping these other selection factors in mind:
• Flutes running all the way to the bit can remove dust more quickly and cut down on heat buildup.
• Bits with a concentric tip can produce smoother holes.
• Centering points help provide more accurate hole starts.
• Generally, the larger the carbide segment, the longer bit life you can expect, if the bit uses high-quality carbide.
• Use the shortest length bit that will accomplish the job. They maximize the blow force generated by the rotary hammer. Shorter bits are also safer to use and cost less.
• Consider frequency of hole drilling and size of the hole. If you seldom drill holes and those you make are less than 5/8", use rotary percussion bits on your hammer drill. More frequent drilling of small holes calls for SDS-Plus bits, while holes bigger than 1 5/8" require spline or SDS-Max bits that can be used in large rotary hammers.

Start with safety
Contractors always want to get more done in a shorter time, but Elsmore reminds: “Safety first! These drills can produce great torque and need to be used with respect.”

To do so, know what you’re drilling into and have the right tools and bits on hand. “When installing anchors or fasteners, use the proper diameter bit so you can install the fastener so it meets its intended purpose. The anchor must fit the hole so you don’t decrease its load-bearing capacity. If you’re unsure about what bit or anchor is appropriate for an application, ask a specialist or call the manufacturer.”

Patrick Kearl, national sales manager at Relton Corp., adds that you should always be careful around water because electrical shock can be deadly. In addition, “Don’t lean on the bit or drill off-axis,” he says. “You could break the bit and fall.”

Our experts agree that you don’t want to hammer-drill through rebar. Carbide-tipped bits aren’t designed for this and can bind or break. In addition, the rebar is there for a reason — check with an engineer when drilling reinforced steel so you don’t cause a structural failure. “Keep a rebar cutter and 1/2" drill handy in case you encounter rebar,” Kearl says. “This way, you don’t need to relocate the hole and drill again. Just drill through rebar with a rebar cutter.

“Never drill deeper than the flutes, either,” he notes. “This can cause the bit to bind because the dust has no way to exit the hole. The bit can bind or break, or the operator could be thrown if the clutch doesn’t engage properly.”

“It’s also important to use the auxiliary side handle on the hammer,” Lawson adds. “If you’re right-handed, firmly grasp the rear handle with your right hand and the side handle with your left. If the tool isn’t held firmly, you can lose control.”

Wearing safety glasses or goggles and gloves are good safe work practices; so is unplugging your tool for bit changes.

“Minimize reach,” Lawson says. “The farther you lean out, the less control you have of the tool.”

Once you’ve approached the job safely, our experts suggest you follow these productivity tips:

• Clear dust and debris by frequently withdrawing the bit while drilling. This is especially important in softer concrete.

• Dust should be visible coming from the hole. If not, use a plunging motion by withdrawing the bit partially to clear dust from the flutes.

• Let the tool do the work. Don’t lean into it or apply unnecessary force.

• Start slow to minimize bit walk.

• Apply pressure gradually until the motor begins to “bog” down. At this point, ease off a little to achieve the correct pressure.

• Maintain a perpendicular angle and minimize side pressure so you don’t get an out-of-round hole and wear the bit’s flutes excessively.

• Grease the shank for less friction inside the hammer drill’s nosepiece. This will allow the bit to slide more efficiently.

• When drilling completely through concrete, make sure to slow down as you reach the backside to prevent sparring or blowout.

• Set depth guides. There’s no need to drill deeper than necessary.

• When working overhead, use a smaller tools (SDS-Plus or hammer drill) if possible, rather than a larger rotary hammer for user comfort.

• Keep carbide insert cutting edges sharp.

• Pay attention to speed. Fast can be good, but too fast can burn the bit, dull it or cause it to fail.

Lawson and Kearl make a final suggestion: Avoid the use of adapters that allow the use of SDS-Max shank bits in a spline-drive rotary hammer. They add mass between the rotary hammer and the bit. A direct-fit bit is always better than an adapter to avoid energy loss.

Published in the September/October 2004 issue of Contractor Tools and Supplies magazine.

back to top