Best Practice for Using Metal Cutting Tools with Large Magnetic and Pillar Drills

A large geared mag drill is the machine for heavy work. It will broach the big holes, drill and tap up to M30 and beyond, ream heavy plate and cut full-depth countersinks, all on steelwork that can't be brought to a workshop. A pillar drill does the same jobs on parts that can.

The difference from a compact is control. With a gearbox, variable speed and reverse, you can run a 100 mm cutter slowly enough to last, and tap blind holes under power. The catch is that every operation needs different settings, and most problems with these machines come from leaving a setting where it was for the last job. This covers the settings for each operation, on any make of geared mag drill or pillar drill.

What a large geared mag drill can do

Using the Steelbor V125T as an example:

The rest of the range steps down through the V100T, V85T and V60T. Check your own machine's capacities before choosing tooling.

Gear first, then speed

Choose the gear for the job, then fine-tune with the electronic speed control. The lowest gear that gets you into the recommended speed range gives the most torque.

• Change gear only with the spindle stopped, and check the selector is fully engaged before starting.
• Change direction only with the spindle stopped. Press stop, wait for the spindle to stand still, switch to reverse, then restart.
• Reset the speed for each new operation. The speed that suited a 22 mm drill bit is far too fast for a 60 mm cutter or an M24 tap.

Typical speeds in structural steel, from the HMT technical guides:

Large cutters and taps need the bottom gear. That low-speed torque is what a compact drill doesn't have.

Secure the machine

• Magnet. Use steel at least 10 mm thick, with a clean, flat contact area free of paint and scale. Make sure both magnet coils are in full contact. Don't share the power supply with other tools.
• Safety strap. Fit it every time. A 25 kg machine dropping off a beam is a serious hazard. In an emergency, hit the motor stop, not the magnet switch. The motor stop leaves the magnet holding.
• Guard and entanglement. Keep the guard closed while cutting, and wear eye and hearing protection. Keep loose gloves, sleeves and jewellery away from the arbor, and only clear swarf ribbons with a hook or brush once the spindle has stopped.
• Pillar drill. Clamp the work to the table or a fixture and keep the chuck guard in place. Never hold heavy sections by hand: a big cutter or tap that grabs will spin the work.
• Slide and arbor. Check them before heavy cuts. Slack in the slide shows up as chatter, oversize holes and chipped teeth.

Annular cutting: large holes

• Centre punch the hole position; the pilot pin locates in the punch mark. No pilot hole is needed.
• Feed gently for the first millimetre, then apply firm, steady feed.
• Choose a cutter deeper than the material. On thick plate, back the rotating cutter out periodically to clear swarf.
• TCT HoleCutters above about 50 mm also belong on a large mag drill or pillar drill rather than a handheld tool.
• Large slugs are heavy and hot when they eject. Clear the area underneath before breakthrough.

See the Steelbor annular cutter range and the Annular Cutter guide for speeds by diameter and material.

Drilling

For twist drilling, fit a chuck, a Morse Taper drill, or VersaDrive tooling via the 111130 Weldon adapter or the 111045 Morse Taper adapter. Pilot anything above 13 mm at about 70% of the finished size. Heavy-duty DrillTaps also need a pilot hole. See the Drill Bit guide.

Reaming

A large mag drill is the right machine for reaming heavy plate. The same rules apply as on any machine: 1–2 mm per pass at most, never start in reverse, and use MAX Reamers in heavy plate. Fit them via a Weldon or Morse Taper adapter.

Flame-cut, plasma-cut and punched holes often have edges harder than the parent metal. Use reduced speed and more feed pressure on a powerful rotary machine; this is where a geared mag drill beats an impact wrench. See the Reamer guide.

Tapping

A geared mag drill with reverse taps far faster than by hand, and up to much larger sizes than handheld tools can manage.

• Through holes: use ImpactaTaps via a Morse Taper or Weldon adapter. Drill the tapping hole and tap it without moving the machine or switching off the magnet, so the tap goes in perfectly in line.
• Blind holes: use a 132-series Morse Taper clutched tapping adapter. Check the stroke has room for both the adapter and the tap. Start in forward with firm pressure and the tap will feed itself in. When the clutch slips at depth, stop the motor, select reverse and restart. Don't let the clutch slip for more than a few seconds.
• Drill and tap in one: Combi DrillTaps work where the machine has variable speed and reverse. The drill and tap sections need different speeds, so check the DrillTap guide.
• Use the lowest gear and SpeedLube. Expect the feed handles to turn as the tap feeds itself in, and again as it reverses out. Keep your hands clear.

Countersinking

Low speed and high torque on a rigid machine give the best countersink life and finish, so this is where large mag drills and pillar drills do their best countersinking. Use HSS or TCT countersinks at the speeds in the Countersink guide. A piloted MultiSink keeps the cutter centred. Clear the swarf so the countersink can't chatter over it.

Lubricant

SpeedLube for tapping, reaming and general broaching. BioCut Blue for hard steels and stainless. In vertical and overhead positions, use BioCut Paste rather than the coolant system, and keep fluid out of the motor. Overhead drilling carries the highest risk if the magnet lets go. Only drill overhead where your machine's manual allows it, with the strap fitted and nobody below. See the full range.

If it goes wrong

Related guides

For lighter work, see our guides to compact mag drills, impact wrenches and pistol drills. The Magnet Drill Training Series has video introductions to the range.

Annular Cutters · Drill Bits · Reamers · ImpactaTaps · Clutched Tapping · DrillTaps · Countersinks · Mag Drill Registration & Warranty