There are three tool options to consider when drilling large-diameter holes in thick steel: twist drill bits, hole saws and annular cutters.
1. Twist drill bits.
Especially in steel thicker than ¼", twist drill bits will require extra pressure, lots of lubrication for cooling and some profanity — especially when trying to use a hand-held drill in an awkward location.
2. Carbide-tipped hole saws.
With adequate lubrication in a drill press, carbide-tipped hole saws can drill through metal that is up to 5/8" thick. Though it’s possible to use a hole saw with a hand-held drill to bore a hole larger than 2" in diameter, there’s a good chance it’s going to kick back and give you a sore wrist.
3. Annular cutters.
Designed to cut large-diameter holes in thick metal more easily and more efficiently than twist drills or hole saws, annular cutters are considered to be industrial-grade tools.
“Twist drills remove all the metal from the inside of a hole,” explains Jonathan Carroll, director of product management for CS Unitec, Inc. “Hole saws and annular cutters remove only a slice around the circumference of the hole. Annular cutters will drill 10-times faster than twist drills of the same diameter, and they require less power from the drill’s motor.”
Hole saws and small-bore annular cutters can be used with hand-held drills, but they are likely to perform better in a drill press where pressure to the cutting edge is able to be evenly applied.
The pilot pin of larger annular cutters has a machined slot that allows automatic oilers on the drill to provide a steady flow of cooling lubricant to the inside of the cut.
Though annular cutters and hole saws are able to be externally lubricated, Carroll explains internal lubrication will give better, more effective results.
“Annular cutters are actually designed specifically for use with magnetic drills with automatic lubrication,” Carroll says. “Their design also uses the pilot pin to help eject the slug after the hole is finished.”
A magnetic drill is essentially a portable 120-volt drill press with a powerful electro-magnetic base. When energized, the magnet attaches the drill to smooth steel or iron surfaces. Mag drills can drill holes up to 6" in diameter in thick metal horizontally or even upside down.
“You can use a hand-held drill and an annular cutter for 7/8" or 1" holes,” Carroll says, “but the operator is going to have to keep it lubricated and hold it in place while he presses the cutter into the hole. Annular cutters work best in drill presses or mag drills, especially for holes large than 1" in diameter in metal thicker than ½".”
