Magnetic Drills (Mag Drills)

Mag drills use an electromagnet (or in some models a permanent magnet) to clamp onto steel while drilling large holes with annular cutters. They make fast, clean holes in beams, plates and pipe. They are also heavy, and the magnet is the only thing holding them. If power is lost or the magnet slips, a drill that weighs tens of pounds can fall or spin violently, taking the cutter, the cord and your hands with it.

• Construction
• Fabrication

How a mag drill works

• A powerful magnet in the base clamps the drill to a steel surface. A separate switch turns the magnet on and off, and the drill motor is controlled by another switch.
• A rack-and-pinion handle feeds the cutter down into the work. An annular cutter (a hollow core cutter) cuts only the edge of the hole and leaves a solid slug in the middle, which is ejected when the cut breaks through. A pilot pin centers the cutter and ejects the slug.
• Cutting fluid or coolant is fed to the cutter to keep it cool and cut cleanly.
• Battery models and models with magnet and motor interlocks exist. Follow your tool’s manual.

What can go wrong

• Loss of magnetic hold. The magnet can lose grip if power fails, if the steel is too thin, if the surface is dirty or curved, or if the cutter binds and the torque overcomes the hold. The drill can then fall, slide or spin.
• The cutter binds. If a cutter catches, the torque spins the whole drill. This hurts hands, tears cords and can throw the tool.
• Hot, sharp slugs and chips. The slug is hot and sharp, and the swarf (chips) is hot, sharp and can cut through gloves.
• Falling tool. On a vertical, sloped or overhead surface, a failed magnet means a heavy drill falls on whoever is below.
• Electrical hazards. A damaged cord, water and coolant around electrical equipment, and a tripped GFCI can all cause shock or loss of the magnet. See GFCI and Wet Locations.
• Entanglement. Loose sleeves, gloves, long hair, jewelry or cords can get caught in a rotating cutter or spindle.
• Heavy lifting and awkward positions. Mag drills commonly weigh 25 to 50 pounds or more. See Lifting & Ergonomics.
• Magnetic fields. The strong magnet can interfere with pacemakers and other medical implants, credit cards and electronics. Keep them away.

Setup: before you drill

• Safety strap or chain secured around the workpiece or a solid support, every time, and especially on vertical, sloped or overhead surfaces. Use the strap the manufacturer provides, rated for the drill’s weight.
• Steel at least as thick as the manufacturer requires for full magnet holding power. Many drills require steel about ½ inch thick or more for full hold. Thinner steel holds much less. Check the manual.
• Contact surface clean, flat, and bare: free of paint, scale, rust, weld spatter, burrs and chips. Even a thin layer or a bit of swarf under the magnet reduces holding force.
• Material large and stable enough that it can’t flex or shift. Clamp or support loose pieces and work on a bench or secured stand where you can.
• Cord in good condition, routed so it can’t wrap around the spinning cutter or catch on something. Use a cord of the right gauge and length. A long thin extension cord causes voltage drop and a weaker magnet.
• Power from a dedicated, GFCI-protected circuit with no other large loads that could trip or sag. If you use a generator, make sure it can supply the drill, and keep generator power steady. See Extension Cords.
• Cutter sharp, the right size and depth rating for the job, and the pilot pin in place. Dull or damaged cutters bind.
• Coolant reservoir filled, and drip protection in place for overhead work.

Drilling

1. Position the drill over the marked center with the cutter just above the surface. Check that the base sits flat.
2. Turn the magnet on first and wait for the indicator light or the manufacturer’s signal that it’s holding. Try to push it gently to test the hold. Never start the motor until the magnet is firmly engaged.
3. Strap the drill to the work if it is vertical, overhead or on an incline, as the manufacturer directs.
4. Start the motor and bring the cutter down gently. Let it start the cut before applying full pressure.
5. Use steady, moderate feed pressure. Don’t force it. Let the cutter cut at its own pace, with cutting fluid flowing. Back off if it chatters or stalls.
6. Ease off near break-through. The slug is about to release and the cutter may grab. Keep your body out of the line where the slug will fall.
7. Stop the motor and let it stop turning before you raise the cutter, touch the work or remove the slug.
8. Turn the magnet off last, and support the drill with your hand before releasing it so it doesn’t drop.

• Wear safety glasses or a face shield, hearing protection, and sturdy boots. See Eye & Face Protection and Hearing Protection.
• Wear close-fitting sleeves, tie back long hair, and remove jewelry. Gloves protect from sharp chips but keep them well away from the rotating cutter. Don’t wear loose or frayed gloves.
• Use a chip hook, brush or magnet with the tool off and the cutter stopped to clear chips. Never use your hands or a rag on a moving cutter.
• Let slugs and chips cool, and handle them with pliers or gloves. Keep the work area clear of slugs and chips so no one trips or cuts a foot. See Slips, Trips & Falls.
• Keep your hands on the handles and your body out of the line of the cutter.

• Don’t drill with no safety strap when the manufacturer calls for one, and don’t rely on the magnet alone overhead.
• Don’t use a mag drill on thin, rusty, painted, curved or non-magnetic material (such as aluminum, stainless steel or cast iron that doesn’t hold) without a proper fixture or a different tool.
• Don’t leave a mounted drill unattended, or turn off the magnet while the cutter is still spinning.
• Don’t drill with the drill on a ladder, a loose plank or an unstable platform. Use a proper work platform or lift. See Scissor Lifts.
• Don’t weld on or near a workpiece with the magnet on, and don’t route the welding return through the drill.
• Don’t change cutters or adjust anything with the drill plugged in and the motor live.

Power loss and cutter bind

• If the power fails or a GFCI trips, stand clear. The magnet may release. Switch everything off, keep your hands off the tool and support it if it’s safe. Don’t restart until the cause is found.
• If the cutter binds, let go of the handles, switch off the motor and don’t grab the spinning drill. Check the workpiece, the strap and the cutter before restarting.
• Some drills have a power-loss feature or a low-voltage cut-out. Don’t depend on it. Always use the safety strap.

Working at height or overhead

• Keep people out from below, and set up a barricade or exclusion zone. Tie off the tool, cord and accessories so they can’t fall. See Fall Protection Basics.
• Expect coolant to drip, and protect yourself and the area below.
• Use a lift or platform, not a ladder, and don’t overreach. Check fall protection rules for the work height.

Care and maintenance

• Check the magnet face before each use. Clean it, and remove burrs or nicks with a flat file or stone as the manufacturer allows. A rough or damaged face loses holding power.
• Inspect the cord, plug, switches, strap and handles for damage. Tag out and repair anything that’s damaged. See Tagging Out Damaged Tools.
• Replace cutters when dull, chipped or cracked, and keep them stored in their cases.
• Follow the maker’s schedule for lubrication, brushes and gibs, and have a qualified technician repair the unit.
• Carry the drill by its handle with the cord secured, use a cart or a second person for heavy tools, and store it dry and clean.

Before each hole

• Steel thick enough, clean, flat and bare under the magnet
• Safety strap or chain on, especially vertical or overhead
• Magnet engaged and holding before the motor starts
• Cord undamaged, on a dedicated GFCI circuit, away from the cutter
• Cutter sharp and coolant on; chips and slugs controlled
• Eye and hearing protection on; loose clothing and gloves kept clear of the cutter
• No one below, and no pacemaker wearers near the magnet

Last updated: October 4, 2026