Magnetic Drill Guide: Mag Base Drills & Cutter Selection

If you've ever tried to drill a 25mm hole through a structural steel beam with a hand drill, you'll know why magnetic drills exist. A mag drill is a portable electromagnetic drilling machine that clamps itself to the workpiece using a powerful electromagnet (or permanent magnet on cordless units) and drills accurate, large-diameter holes through steel — on the beam, in the column, overhead, vertical, or upside-down — with the same precision as a stationary drill press. This guide covers every mag drill stocked at AIMS — Metabo German premium, Excision AU mid-tier, and Bordo AU value-to-premium — the annular cutter technology that makes them work, the magnet-hold physics that determines safety, AS 1418 portable-power-tool requirements, and the forum-validated practitioner reality from boilermakers, structural steel fabricators and mining service technicians who use these tools daily.

Honest scope: AIMS stocks 9 mag drill products across Metabo + Excision + Bordo, in our magnetic drills collection. AIMS does NOT stock Hougen (US — the inventor of annular cutter technology), FEIN, Milwaukee M18 cordless mag drill, Nitto, BDS (German specialty importer), Slugger, Jancy, Evolution, Baileigh — these are specialty/premium imports flagged source-on-request via our supplier network. AIMS now stocks 32+ annular cutter products in the Annular Cutters & Sets collection across Bordo, Sutton Tools, Euroboor, Alpha and Maxbor — see the Annular Cutter Guide for shank standards, pilot pin function, HSS vs TCT, sizing and selection. We also stock cutting fluids and associated safety PPE for mag drill operations. Position Bordo + Excision as comparable AU industrial-tier alternatives to Milwaukee + FEIN + Hougen for fabrication and structural steel work.

What is a Magnetic Drill and When Does It Beat a Hand Drill?

A magnetic drill (mag drill, mag base drill, magnetic core drill, electromagnetic drilling machine) is a portable power tool with three integrated parts: an electromagnet base, a vertical drill slide with travel handle, and a drilling motor with arbor that accepts annular cutters (or twist drills via a chuck adapter). The electromagnet locks the entire unit to ferrous metal — typically structural steel, plate, beam, pipe — with thousands of newtons of hold force. The operator then advances the drill into the workpiece using the handle, just like a benchtop drill press.

The mag drill exists because there is a category of drilling job that cannot be done well by hand and cannot be done at all by a stationary drill press:

The killer use case is steel-already-in-place — beams set in a bridge, columns standing in a building, plate welded into a vessel, manifolds installed on machinery. You can't bring those workpieces to a drill press; you have to bring the drill to them. The mag drill is the only tool that does this with drill-press accuracy.

Annular Cutters vs Twist Drills — How Mag Drills Actually Cut

Most mag drill operators use an annular cutter (also called a core drill, broach cutter, or RotaBroach — the original Hougen trademark term) rather than a twist drill. The annular cutter is the technology that makes the mag drill productive. Understanding what it does and why it's different from a twist drill is the single biggest gap for first-time mag drill buyers.

A twist drill cuts the entire hole — it removes all the material as chips. Drilling a 25mm hole through 20mm plate means cutting all the steel in a 25mm × 20mm cylinder into shavings.

An annular cutter only cuts the outer ring of the hole. The centre of the hole comes out as a solid slug — like a core sample. Cutting only the outer ring means:

• Less material removed — only the ring, not the full cylinder volume. A 25mm annular cutter through 20mm plate removes about 60% less material than a 25mm twist drill.
• Less torque — less material being cut means less motor power required. A mag drill motor can be smaller than the equivalent twist-drill drill press for the same hole size.
• Faster cutting — less material means faster hole completion. A 25mm annular cutter through 20mm plate takes 30-60 seconds; a twist drill of the same size in the same plate takes 3-5 minutes.
• Cleaner hole — annular cutters produce a true cylindrical hole with parallel walls. Twist drills produce a slightly conical hole because the cutting lips engage gradually.
• Reusable slug — the slug ejects as a clean disc that can sometimes be re-used (washers, blanks, test coupons).

Annular cutters need a pilot pin through the centre. The pilot positions the cutter accurately on the workpiece, provides initial centring, and as the cut progresses retracts upward into the arbor. When the slug is freed, a spring in the arbor ejects it. Hougen's original 1980s design established this mechanism and most modern annular cutters follow the same convention.

Annular Cutter Materials — HSS vs TCT Carbide

Annular cutters come in two main material grades, and the choice depends on the steel you're cutting, not the marketing claims:

The Hougen rule (forum-validated consensus): HSS handles 80% of fabrication jobs. TCT carbide is wasted money on standard mild steel — the carbide only earns its keep when cutting hard or abrasive material at higher RPMs. Buying TCT for "best tool life" on mild steel is a false economy.

Coolant System — Why External Spray Doesn't Work

Most mag drills have a built-in coolant reservoir that feeds cutting fluid through the cutter — down the centre tube and out the cutting edges. This internal coolant delivery is the single most important factor in annular cutter tool life.

Hougen direct quote: "Spraying or squirting coolant at the cutter while it is turning does very little in helping tool life — most of the coolant is pushed aside by the chips and flutes before it reaches the cutter. For best results use the mag drill's coolant system."

Workshop reality: many fabricators run their mag drill dry on quick site jobs or use a spray bottle for top-up. This dramatically shortens cutter life — particularly on stainless and hardened steel. A 30-second job dry on stainless can blunt a $150 cutter; the same job with proper internal coolant flow extends cutter life to 50+ holes. Workshop economics: buy good cutting fluid, use the coolant system, change cutters less often. AIMS stocks a comprehensive range in our cutting fluids collection — see the dedicated cutting fluids guide for selection by material.

Magnet Hold Physics — Why 6-8mm is the Minimum

An electromagnetic mag drill base hold-force is typically rated 9,000-25,000+ N (newton) on clean, flat, 25mm-thick mild steel. The catch is that hold force depends entirely on material thickness, surface condition, and contact area:

Better mag drills (Metabo MAG 32/50, premium Bordo, Excision) include a reed switch or hall-effect sensor that detects whether the magnet base is making proper contact. If the unit detects a poor contact — paint, scale, rust, curved surface, undersize plate — the safety circuit prevents the drill motor from starting. This protects against the classic mag drill failure mode where the operator engages the magnet, the magnet only partially grips, the operator starts drilling, and the cutting torque tears the drill off the workpiece.

The Safety Chain — Non-Negotiable for Vertical and Overhead Work

Every mag drill ships with a safety chain or strap. The chain wraps around the drill body or a designated lift point and clips to a secure anchor on the structure being drilled. If the magnet drops (power failure, generator stall, motor interlock trigger, electrical fault), the chain catches the drill before it falls.

Cordless mag drills changed this calculus. Milwaukee M18 FUEL and similar cordless units use permanent magnet bases rather than electromagnets. Even if the battery dies or is removed, the magnet keeps holding — Pro Tool Reviews calls this the "dead-man" feature. The safety chain is still recommended for vertical/overhead work, but the cordless permanent-magnet design removes the single biggest failure mode that has caused most mag drill drops. AIMS doesn't currently stock cordless mag drills (Milwaukee M18 mag drill is the global cordless reference); the corded Metabo + Excision + Bordo range we carry includes safety chains and is the AU industrial workshop standard for mains-powered fabrication.

Mag Drill Sizing — Capacity by Cutter Diameter

Mag drills are typically sized by maximum annular cutter diameter the unit can swing. The capacity rating describes the largest hole the unit's motor + slide travel can produce:

Practical sizing rule: buy the size you need for 90% of jobs, not the maximum you might ever need. A 50mm-capacity unit can drill 8mm holes but is heavier, more expensive, and more cumbersome than a 35mm unit. For fab shops doing typical bolted-connection work, 32mm or 35mm covers most jobs. For heavy structural, bridge, or mining service, 50mm is the standard. The Bordo MAG100 100mm-capacity is specialty equipment for bridge, rail bridge plate, or major structural fabrication.

Brand Reality — Stocked vs Source-on-Request

Mag Drill Operation — Step-by-Step Procedure

1. Prepare the workpiece. Clean the contact area — remove paint, scale, rust, dirt, grease, weld spatter. A wire brush (see the wire brush guide) and degreaser are the standard prep. The cleaner and flatter the steel, the higher the hold force.
2. Position the drill. Mark the hole centre. Position the mag drill so the pilot pin aligns with the mark. Most mag drills have a notch or pointer on the base for centring.
3. Rig the safety chain. Mandatory for vertical, overhead, or angled work. Wrap the chain through the drill carrying handle or designated anchor point and secure to a structural attachment. Test by lifting the drill slightly against the chain before engaging the magnet.
4. Engage the magnet. Press the magnet switch. A reed-switch-equipped drill will indicate good or poor magnet contact. If the indicator shows poor contact, stop — clean the surface further or reposition.
5. Test the hold. Try to slide the drill on the workpiece with firm hand pressure. It should not move. If it slides, the magnet is not properly seated — stop and re-prep.
6. Fit the annular cutter and pilot pin. Insert the pilot pin through the cutter centre. Insert the cutter into the arbor and lock (most use Weldon shank — flat ground on the shaft, locked by grub screws in the arbor).
7. Engage coolant. Open the coolant valve and prime the internal feed. The first drop of coolant should appear at the cutter teeth before drilling starts.
8. Start the drill motor and lower the cutter to touch the workpiece. Establish initial contact with light feed pressure.
9. Feed the cut. Use the handle to advance steadily — solid, even pressure. The chips should be continuous coiled ribbons (good feed) or short curls (acceptable). Powder-like chips mean the feed is too light; long stringers mean the feed is too heavy.
10. Watch the chip flow. If chips stop flowing, stop the cut and clear the cutter. Trapped chips can break the cutter or damage the hole.
11. Finish the cut. When the slug breaks free, the resistance drops sharply. Stop the feed, retract the cutter, and remove the slug (it will eject from the arbor on most cutters as the spring releases).
12. Release the magnet. Turn off the magnet switch. The cordless permanent-magnet types use a lever or mechanical release; the corded electromagnet types simply de-energise.
13. Move to the next hole or pack up. The annular cutter should be wiped clean and the coolant reservoir refilled before storing.

Twist Drills in a Mag Drill — When and How

Mag drills with arbor adapters or interchangeable chucks can run twist drills as well as annular cutters. This is the right choice for:

• Small holes (3-13mm) where annular cutters aren't readily available or economic
• Pilot holes for follow-up annular cuts or reaming
• Deep holes that exceed annular cutter slug depth (typically 50-75mm)
• Tapping after drilling — the same mag drill can drill the hole and run a tap if speed-controlled

For drill bit selection, see the choosing the right drill bit guide and the drill bit types guide. For cutting speeds, see the cutting speeds and feeds chart.

Mag Drill PPE and Workshop Setup

Mag drill operation generates hot chips, sometimes flying chip ribbons, and the unique hazard of a heavy power tool secured to vertical or overhead steel. PPE requirements:

• Safety glasses — mandatory. Hot chips fly at face level on horizontal cuts. AS/NZS 1337-compliant. See safety glasses guide. AIMS stocks a full range in our eye protection collection.
• Hearing protection — mag drill motors typically run 85-95 dB at the operator position. AS/NZS 1269 mandates protection above 85 dB. See hearing protection guide.
• Safety boots — chip and slug drop hazard. Steel toe minimum. See safety boots guide.
• Welding gloves or cut-resistant gloves — for handling hot chips, hot slugs, and the cutter after use. NOT thin nitrile or general-purpose gloves — the chips are sharp and hot.
• Hard hat for overhead work — chips and slugs falling from above. AS/NZS 1801. See hard hat guide.
• Hi-vis vest for site work and structural fabrication. AS/NZS 4602. See hi-vis vest guide.
• Workshop area cleanup — chip swarf, slug containment, coolant control. A Mistake Consequence Fix No safety chain on vertical/overhead work Drill drops if power fails — injury or loss Chain every time, no exceptions Drilling 4-5mm sheet Magnet won't hold under cutting torque 6-8mm minimum; use hand drill or clamp-and-drill on thinner sheet Magnet on paint/scale/rust Reduced hold; drill walks under load Wire brush and degrease the contact area Trying to drill aluminium/stainless 304/316 base material Magnet won't hold — non-ferrous Use drill press or magnetic adapter plate; stainless workpiece on steel base plate works Letting off feed pressure mid-cut on stainless Work-hardening — cutter can't re-engage Solid steady feed, plenty of coolant, finish the cut Spraying coolant externally instead of using internal feed Coolant pushed aside by chips, doesn't reach cutting edge Use the mag drill's coolant reservoir + internal feed TCT carbide cutter on mild steel at HSS RPM No benefit — carbide needs higher RPM to perform HSS for mild steel; TCT only on hard/abrasive material at carbide RPM Forgetting the pilot pin Cutter chatters; slug doesn't eject cleanly Pilot pin every cut — small disposable insurance Cutting on a curved pipe surface without a pipe clamp Magnet contact is line-not-surface; very low hold force Use pipe drilling clamp accessory (V-block adapter) for curved surfaces No PPE — gloves, eye, hearing Hot chips at face/hands/ears; 85-95 dB exposure Glasses + earmuffs + welding/cut-resistant gloves minimum

  AIMS Mag Drill Range — Supply Ladder

  Workshop entry tier ($1,266-$1,669): Bordo MAG35 ($1,266) is the entry to AU-tier mag drills; Excision EMB 35 Fabricator's Kit ($1,291) bundles cutters and accessories; Excision EM40 ($1,669) steps capacity to 40mm. Best fit for fab shops getting their first dedicated mag drill, mobile maintenance trades, and small structural fabricators.

  Workshop standard tier ($2,007-$2,726): Bordo MAG50 ($2,007) extends capacity to 50mm; Excision EM50 ($2,551) is the heavy-duty Excision option; Metabo MAG 32 ($2,726) brings German engineering at 32mm capacity. Best for production fab shops, structural workshops, mining service.

  Premium tier ($3,699-$4,541): Metabo MAG 50 ($3,699) at 50mm capacity with 1200W; Metabo M 100 Electromagnetic Drill Stand ($4,005) for stand-mounted heavy work; Bordo MAG100 ($4,541) for 100mm-capacity bridge/heavy-structural work. Best for bridge fabrication, heavy structural steel, rail, mining production.

  For pricing on Hougen, FEIN, Milwaukee M18 cordless mag drill, Nitto, BDS, Slugger, Jancy, Evolution, or Baileigh — these are specialty imports we can source via our supplier network. Contact the AIMS trade team or call (02) 9773 0122 for sourcing and pricing.

  Selection Checklist

  1. What's the largest hole you need to drill? Add 25% headroom — sizing the unit at capacity leaves no margin for the occasional bigger job.
  2. Plate thickness? 6mm minimum for the magnet. If most of your work is 3-5mm sheet, mag drill is the wrong tool.
  3. Material? Ferrous only for the magnet base. Stainless/aluminium workpieces clamped on a steel base plate can work.
  4. Where will you drill? Bench-only = drill press is cheaper. On-site, overhead, vertical, in-situ = mag drill territory.
  5. Mains power available? If yes — corded works. If on remote sites, scaffold, or bridge work — cordless makes sense (Milwaukee M18, source-on-request).
  6. Volume of holes? Production fab = step up to Metabo or Excision. Occasional use = Bordo or Excision entry.
  7. Cutter material? HSS for 80% of jobs (mild steel, low alloy). HSS-Co for stainless. TCT only for hard/abrasive at high RPM.
  8. Pipe drilling? Specify pipe drilling clamp accessory or V-block adapter.
  9. Compliance: AS 1418 (portable power tools), AS/NZS 3760 (test and tag), AS 1337 (PPE eye protection), AS 1269 (noise exposure).

  Frequently Asked Questions

  What is a magnetic drill used for?

  Magnetic drills are designed for drilling accurate, large-diameter holes in ferrous metal (steel, structural steel, plate, beam, pipe) where the workpiece can't move to a drill press. Typical applications: structural steel fabrication, on-site bridge and bolt-hole drilling, beam and column drilling in-place, mining and rail service maintenance, manifold and vessel drilling, heavy plate work. Not for thin sheet (below 6mm), non-ferrous material (aluminium, brass, stainless 304/316 as base), or general workshop drilling where a drill press is available.

  How thick does the steel need to be for a mag drill to hold?

  6mm minimum, 8mm preferred, 12mm+ for rated hold force. Below 6mm the magnet's flux path is too thin to develop full holding force and the drill will release under cutting torque. Forum + manufacturer consensus: target 8-10mm minimum for safe production work; rated hold figures assume 25mm flat clean plate.

  What's the difference between an annular cutter and a twist drill?

  A twist drill cuts the entire hole (removes all material as chips). An annular cutter cuts only the outer ring — leaves the centre as a solid slug. Annular cutters remove ~60% less material than equivalent twist drills, require less motor torque, cut 5-10× faster, and produce a cleaner cylindrical hole. The slug ejects on completion. Pilot pin retracts into arbor as the cut progresses. Annular cutters are the standard cutting tool for mag drill work.

  Do I need HSS or TCT carbide annular cutters?

  HSS handles 80% of fabrication jobs — mild steel, structural steel, low-alloy steel at standard mag drill speeds. HSS-Co (cobalt HSS) is the upgrade for stainless and harder alloys. TCT (tungsten carbide tipped) needs higher RPM than standard mag drills run and only earns its keep cutting hard or abrasive material — wasted money on mild steel. Hougen consensus: HSS first, upgrade only when material justifies it.

  Why is the safety chain critical for overhead work?

  Electromagnet mag drills lose their hold the instant power is lost — generator stall, breaker trip, fault, cable damage. If the drill is overhead or on a vertical surface, the loss of magnet means the drill falls. An industry-cited incident has approximately 40 drills dropped into the East River when a bridge rehabilitation contractor lost site power mid-job. The safety chain secures the drill to the workpiece so it can't fall. Mandatory for vertical, angled, and overhead drilling.

  What is the difference between corded and cordless mag drills?

  Corded mag drills use electromagnets — require continuous mains or generator power. If power fails, magnet drops, drill falls. Cordless mag drills (Milwaukee M18 FUEL, source-on-request) use permanent magnets that keep holding even when the battery is removed — Pro Tool Reviews calls this the "dead-man" feature. Cordless removes the single biggest fall-risk failure mode but adds battery-life and cost considerations. AIMS currently stocks corded only; cordless is a specialty import via our supplier network.

  Can I drill stainless steel with a mag drill?

  Yes, but stainless is the hardest workshop material to drill well. Three rules: (1) use HSS-Co or TCT cobalt-tipped cutters, not standard HSS; (2) use plenty of coolant via the internal feed system; (3) solid steady feed pressure — never let off mid-cut. Stainless work-hardens rapidly; if you reduce feed and let heat build, the cut surface hardens to the point the cutter can't re-engage. Hougen + WeldingWeb consensus: once started, finish the cut without pause.

  Why won't my mag drill hold on this surface?

  Most common reasons in order: paint/scale/rust on the contact area (reduces hold 20-40%); curved surface (line contact not surface contact — needs pipe clamp); workpiece too thin (below 6mm); workpiece is non-ferrous (aluminium, stainless 304/316 — magnet won't hold at all); or contact area too small for the base footprint. Fix: wire brush + degrease, use proper pipe clamp on curved surfaces, check plate is ferrous and 6mm+, ensure the entire magnet base contacts steel.

  What annular cutters does AIMS stock?

  AIMS doesn't currently stock annular cutters in a dedicated collection — cutter sourcing is handled by direct enquiry through our trade team. We stock the mag drills, the cutting fluids they use, and the PPE for operators. For cutters, contact the AIMS trade team with size, material and quantity and we'll source through our supplier network.

  How do I clean and maintain my mag drill?

  Daily: wipe magnet base, drain coolant reservoir if overnight storage. Weekly: inspect arbor lock screws, safety chain, slide rail lubrication. Monthly: motor brush check (corded), magnet hold-force test (Hougen test = 25kg coupon on flat steel — if hold marginal, service or re-magnetise). Pre-shift: confirm magnet activation, coolant flow, motor function, slide travel, arbor lock.

  What's the difference between mag drill capacity 32mm vs 50mm?

  Capacity refers to the largest annular cutter the unit can swing. 32mm capacity covers general fab and structural up to that size hole. 50mm steps up to heavy fab, bridge, mining service — bigger motor, bigger frame, heavier unit. Practical sizing: buy for the 90% of jobs, not maximum. 32-35mm covers most fab shops; 50mm for heavy structural; 100mm for bridge/rail/heavy plate.

  Can a mag drill replace a drill press?

  For most workshop drilling on parts that fit a drill press, a drill press is faster, cheaper, and more accurate. Mag drills exist for jobs the drill press can't do — workpieces too large to move, in-situ structural work, overhead/vertical drilling, on-site bolt-hole drilling. The two tools complement each other; they don't replace each other.

  What's the right RPM for mag drill annular cutting?

  Material and cutter material dependent. Mild steel with HSS annular cutter: 200-700 RPM depending on diameter (larger = slower). Stainless with HSS-Co: 30-50% slower than mild steel. TCT carbide: 2-3× HSS RPM — needs a high-speed mag drill or two-speed gearbox. Most fab-shop mag drills (Metabo MAG 32 single-speed) target mild steel HSS; high-speed work needs the geared range (Metabo MAG 50, Bordo MAG50, Excision EM50). See the cutting speeds and feeds chart for full reference.

  Are AS/NZS standards relevant to mag drill operation?

  Yes. AS/NZS 60745 / AS/NZS 62841 cover portable power tool safety. AS/NZS 3760 covers electrical test-and-tag for workplace tools. AS/NZS 1337 covers eye protection PPE. AS/NZS 1269 covers noise exposure (mag drills typically 85-95 dB — hearing protection mandatory above 85 dB). AS/NZS 1801 covers hard hats for overhead drilling sites. Workshop safety compliance bundles these standards with WHS regulations (WHS Act 2011, WHS Regulations 2017 per state).

  What associated tools and consumables does a mag drill workshop need?

  Annular cutters (sized for jobs), pilot pins (matched to cutters), Weldon-shank arbors (sized to drill — usually 19mm or 3/4"), cutting fluid (internal feed compatible — see cutting fluids guide), wire brush and degreaser for surface prep, PPE (safety glasses, hearing protection, safety boots, welding gloves, hard hat, hi-vis vest), safety chain (usually included), pipe drilling clamp accessory if doing pipe work, and a workshop vacuum or chip tray.

  For complete fabrication and structural steel workshop context, see our companion guides: choosing the right drill bit, drill bit types guide, cutting speeds and feeds chart, cutting fluids guide, MIG welding guide, stick welding guide, wire brush and wire wheel guide.

  Need help selecting the right mag drill for your fabrication workshop or specific structural steel application? Browse the full magnetic drills collection, call AIMS Industrial on (02) 9773 0122, or contact our trade team — we'll match the unit to your application, source specialty brands (Hougen, FEIN, Milwaukee, Nitto, BDS) through our supplier network, and quote on annular cutter requirements.

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