Making big holes in big steel

Annular cutters can do the job efficiently

Working with structural steel almost always requires bigger tools, greater brawn and good job planning. When it comes to making holes in structural steel, that’s even more true, say hole-making experts.

“If the requirement is for consecutive holes over a period of time or in thick metal, then an electromagnetic drill press and annular cutter would be the most economical and efficient system,” says Dave Duecker, metal working project manager at Milwaukee Electric Tool.

Also known as mag drills, these units offer the precision of a drill press when they lock onto the work surface with their magnetic bases.

Annular cutters can drill faster than a standard twist bit because they remove only the outer edge of the hole; the inner portion is ejected as a slug. “They make high-quality, burr-free holes without bit wandering,” Duecker adds.

Where magnetic drills are a good match
Mag drills and annular cutters are a good match for 7/16" to 3" diameter holes in any steel 3/8" to 3" thick. “I estimate that 90 percent of the mag drills in use today are used on structural steel,” says Ben Ruppel, Hougen field and technical support representative. “Structural steel has inconsistencies so it may cut differently, even in the same piece of steel,” he says.

Several factors affect hole-making in steel, says Carl Gunderson, director of sales and marketing at Universal Drilling USA, Ltd.

“Hardness of material, abrasion resistance, machine horsepower, lubrication, speed and feed rate all affect the efficiency of making holes with an annular cutter. Typically, harder materials need to be cut at lower speeds depending on the cuter diameter. Choosing the right amount of cobalt content can enhance cutter performance and tool life,” he says.

The cutting process is based on feel, the experts report. Rely on manufacturer information to match speed to the cutter diameter.

Cutting tips
There isn’t just one big thing that affects annular cutting success. Instead, many little things can impact cutting speed and cutter life.

Keep the cord short. “When using a mag drill, don’t use miles of extension cord to power the tool. Refer to the tool’s instruction manual to match the gauge of the extension cord to the length of run,” suggests Ruppel.

Select the right cutter. There are a variety of annular cutters available. “All react differently to speed and feed,” says Lowell Frey of Champion Cutting Tool. “Pushing the tool into the workpiece too slowly will polish the cutting edges; pushing it in too fast will break or shatter the cutter.”

M2 high-speed steel cutters can yield 500 or more lineal inches of cutting; cutters with 5 percent cobalt can achieve as much as 30 percent more lineal inches between sharpenings, reports Gunderson.

Use a sharp cutter. For greatest efficiency and safety, Ruppel recommends using a sharp annular cutter. “A sharp cutter that’s being fed correctly into the workpiece will make long, stringy chips that form a bird’s nest around the cutter. If you are getting fine shavings, the cutter is dull and needs to be sharpened,” he says.

Get good magnetic base contact. Mag drills work best on 3/8" or thicker steel that is free of paint, rust or metal chips, says Ruppel.

“Keep the work surface clean. Because the magnet is what clamps the tool to the work surface, it needs the most metal-to-magnet contact possible for a good hold. If you are cutting holes near each other, brush off the chips before you reposition the mag drill,” he says.

Be ready to rotate. On high-production jobs, Ruppel recommends having six cutters for each mag drill in use. “Have two ready to cut, two in reserve and two out being sharpened. Rotate them in and out of service,” he says.

Use coolant. Annular cutting in principle is a machining process. That means coolant is needed for greatest efficiency and longest cutter life, says Frey. “Cutting without fluid will dramatically shorten the life of the cutter,” he says.

Base feed rate on feel. It’s really a matter of feel that comes with experience, say the experts.

“Don’t try to force the cutter through the material. This can cause friction that will generate heat and, in turn, reduce tool efficiency. It can even break the tool,” says Gunderson.

If you hit a hard spot in the metal, ease off and lower the speed slightly until you get through it, he suggests.

Maintain the tool. Although these are rather expensive tools, they are straightforward in design and can be easily maintained by the user. “Occasionally, put a few drops of oil on the slides to keep them working smoothly. Keep nuts or bolts tight. Check the owner’s manual for specific maintenance information on your mag drill model,” Ruppel says.

When to call the experts
Magnetic base drill companies and annular cutter manufacturers have troubleshooters on staff who can help you if you run into problems.

Similarly, your distributor can help you find the answers you need to make big holes in big steel safely and efficiently.

Published in the July/August 2003 issue of Contractor Tools and Supplies magazine.

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