On a magnetic drill, an annular cutter runs rings around a twist bit. Because it only removes material at the rim and leaves a solid slug in the centre, the best annular cutters cut large holes in steel faster, cooler and with far less effort than a solid drill grinding the whole diameter into chips.
What to Look For
Start with the shank type, which must match your mag drill arbor so the cutter seats and locks correctly under load. Cutting depth matters next, since every cutter is rated for a maximum material thickness and forcing a deeper cut invites trouble. Check the material of the cutter itself. High-speed steel suits most structural steel, while tougher grades benefit from harder cutter material. A quality cutter needs a pilot pin to eject the slug at the end of the cut and to guide coolant straight into the teeth where it is needed.
Our Top Pick
For structural steel on a mag drill, a high-speed steel annular cutter sized to your most common hole diameters is the reliable workhorse choice. It clears large holes quickly and leaves a clean, ready-to-use bore that often needs no further work. American-made cutters are ground to consistent tooth geometry, which keeps the cut smooth and the finish clean across beams, plate and flange work all day long.
- Shank: match the arbor on your magnetic drill exactly.
- Depth: confirm the cutter suits your material thickness.
- Pilot: the pin ejects the slug and feeds coolant in.
- Coolant: lubricate the cut for a cleaner bore and longer life.
Why Annular Beats a Twist Drill
A twist drill must convert the entire hole into chips, which takes power, generates heat and slows badly as the diameter grows. An annular cutter only machines a narrow ring at the edge, so it needs far less force, runs noticeably cooler and finishes large holes in a fraction of the time. The leftover slug drops clear when the pilot pin ejects it, and the resulting hole is clean enough for bolts or light reaming with very little extra work at the bench.
Running Them Well
Let the mag drill grip firmly on a clean, flat surface before you start the cut, and keep coolant flowing through the pilot into the teeth. A steady feed keeps a continuous chip forming and stops the teeth from rubbing and glazing. Ease off gently as the cutter breaks through the far face so the slug ejects cleanly rather than jamming in the bore. Cared for this way, a single cutter delivers many holes at the same clean, accurate quality. Keep a spare pilot pin on hand as well, because the pin does the quiet work of centring the cut and springing the slug free, and a bent or lost pin can idle an otherwise perfectly good cutter until you can source a replacement for it.