Drill sergeants

Drill sergeants

Experts share sure-fire tips for dead-eye hole making in metal, wood and concrete

If you attack every hole you make in the same fashion, you are going to end up with less than optimal results, report holemaking experts.

Contractor Tools and Supplies asked experts – drill sergeants in their own right – about common mistakes or misunderstandings workers often have about making holes in various types of material. Here’s some basic training that can whip any platoon of holemakers into taking on any drill.

In metal:
Metal drilling can damage bits, reports Scott Roussin of Norseman Drill and Tool. “A broken bit is a sign of misuse. It’s often caused by using a bit as a reamer or by catching the bit in the hole,” he says.

The telltale sign of reaming with a bit is wear marks on the land, or high surface, of the bit.

If the bit is catching in the hole, you’ll see bite marks from the chuck on the flats of the bit shank. “If the shank is round, you’ll see slip marks on the shank,” Roussin says.

If the bit has chipped points, the worker is catching the bit in the hole or enlarging a hole with a split-point bit. “If the point looks burned, the user is running the bit too fast for the bit size and the material hardness being drilled such as drilling 1/4" holes in stainless or hardened steel,” Roussin says.

Alan Peterson, M.K. Morse product manager, says metal drilling is most productive with proper speed, consistent feed pressure and on thick holes, cutting lubricants.

Ed Pchola, Bosch Power Tools and Accessories group product manager, agrees. “Too much pressure can lead to poor hole quality, snapped bits and shorter bit life. Bits with coatings can prevent rusting, provide lubricity and add to bit life. In abrasive materials such as cast iron or stainless steel, a cobalt bit offers the best balance between productivity and long life,” he says.

“If you’re making a larger hole in sheet metal, a step-drill bit is the tool of choice,” says Peterson. “Keep the bit straight and level and use consistent speed. Do not overfeed or you’ll risk making the hole too large. If you’re drilling many holes of the same diameter, mark the shoulder of the step diameter so it’s easy to see when you’ve drilled far enough.”

Peterson cautions against using a step drill in thick metal. “They are not like split-point twist drills. If you drill into material that is thicker than the height of the shoulder of the diameter of the step drill, you will end up with a tapered hole,” he cautions.

In wood:
“There are spade, auger, and twist drill bits you can use. Use the right bit for the job and use it at the right speed. Make sure it is sharp,” says Jason Feldner of Bosch Power Tools and Accessories. “The drill doesn’t need high torque. Correct speed is most important and make sure the material gets out of the hole. If it’s a spade bit, pull the bit out of the hole to clear the shavings.”

Auger bits are the right bit for making holes in wood or nail-embedded wood, says Peterson. “Keep the bit straight and/or level and use consistent speed and pressure while boring. Double-fluted bits work best, but there is a misconception that ship auger bits are the same as double-fluted boring bits and that auger bits will not cut nails. They can,” he says.

“Understanding the difference between the two bits is important,” says Pchola, “Spur augers are for fast, clean holes where you are sure you won’t hit nails. Ship auger bits are used where nail hits are possible. They provide durability, but the hole will be as clean as one made with a spur auger bit.”

Spade bits are low-cost bits for wood-boring jobs. “Steady and consistent feed pressure and speed are important. Pay attention to the bit and work it, varying pressure to produce the best wood chip for the density of the wood,” Peterson says.

Carbide-tipped hole saws can cut wood, composite materials and fiberglass. To get a quality hole, Peterson says it takes cutting at the proper speed and using even, consistent feed pressure. “When using hole saws, use a slight orbiting action as you feed it into the wood. When cutting vertically in thicker wood, back the hole saw out of the cut periodically to allow chips to exit,” he says.

“Users often believe that straight and heavy force or pressure at maximum drill speed will produce the fastest hole or that a hole saw can bore through deep materials like an auger or spade bits or twist drills. Neither is true,” Peterson says.

In concrete:
“Avoid hitting rebar if at all possible,” recommends Feldner. “If you have a detector that can find rebar, use it. Most are able to find rebar embedded as deep as 4". On high-production jobs, use a rotary hammer instead of a hammer drill and use the right-sized tool. If you are drilling a 1" hole, for example, step up to a 1 1/16" drill. When you upsize the tool, you hit the tool’s productivity sweet spot,” he says.

Bit selection is important. “Make sure the bit is sharp. Some companies sharpen their hammer drill bits so they can be used in multiple materials. Precision is important, especially in anchoring applications,” says Feldner. When drilling into concrete, look for bits with multiple flutes, he adds. “When combined with a sharp bit, you will drill and remove dust faster.”

Eric Fernandes, senior product manager at Milwaukee Electric Tool, recommends using SDS bits that have a four-fluted spiral design that removes concrete dust faster and are stronger for smoother holes and faster drilling time. “Also, look at hammer drill bit sets with three flats on the shank. They maintain chuck jaw contact with the flats and prevent the bit from hanging up under heavy loads. Round shank hammer drill bits can spin in the chuck under heavy loads.”

Cordless tools can now be used for production drilling jobs, and Fernandes says the amp-hour rating of the battery is a good indicator of how many holes can be drilled on a charge. “For example, our V28 compact rotary hammer with a 3.0 amp-hour battery can drill 326 1/4" x 3/4" deep holes per charge or 159 1/2" x 3/4" deep holes per charge. The V28 compact rotary hammer is also rated to handle up to 1" solid bits and up to 2 1/2" thin-walled core bits,” he says.

For concrete drilling applications, Fernandes also recommends using the shortest bit possible because it helps concentrate the bpm and improve productivity. “Short bits cost less and increase performance. Depending on your body position, they can also be easier on your back.”

Use fresh bits for best results
Mark Ziegler, director of engineering at Powers Fasteners, says a common problem with drilling in concrete is workers using a worn bit that, in turn, creates an undersized hole. “The worker thinks he is doing a good thing by using a worn bit to save money, but it is really creating an undersized hole. It takes longer to drill a hole and can create installation problems,” he says.

Drilling deep or large holes in concrete can create bit wandering if you use a standard tip design, cautions Ziegler. “The standard tip design will wander in the hole while drilling deep holes. To prevent this from happening, use a bit with an optimized design like Powers’ Tri-Cutter bit. It has a unique head configuration that increases drilling speed and creates a straighter hole. There is also less vibration with this bit because it evacuates dust from the hole more efficiently. It’s also durable if it hits rebar,” he says.

Carbide grit hole saws can be used on masonry, tile, fiberglass and laminates, but not hard metals such as stainless steel. “With these hole saws, drill a pilot hole before using the hole saw. Use steady but not excessive pressure to allow the hole saw to cut without heat build-up. “Sometimes coolant can be used when making holes in masonry, stone or tile to extend the life of the hole saw,” Ziegler adds.

Published in the March/April 2007 issue of Contractor Tools and Supplies magazine.