Using Large Bits on A Pillar Drill

This an early draft and some sections may not match with our pillar drill

Drilling metal produces sharp, high-velocity spiral chips that can fly in any direction. These chips are hot and have razor-sharp edges. Goggles prevent blindness from a chip ricocheting off the drill column into your eye. A visor also protects your forehead and cheeks from larger, heavier chunks that might break off during breakthrough.

Large bits (typically over 13mm / ½ inch) displace a huge volume of metal per revolution, causing severe vibration and structural resonance through the machine and workpiece. Prolonged exposure to noise above 85 decibels causes irreversible cumulative hearing loss. Furthermore, wearing earplugs reduces fatigue, allowing you to concentrate better on the feed pressure.

A pillar drill generates massive torque (turning force). If a glove finger, a sleeve cuff, or a ring snags on the rotating bit or chuck, the machine will not stall; it will win. It will instantly twist your hand, finger, or entire arm around the spindle at high speed, causing spiral fractures, or arm amputation before you can even react.

Loose hair acts like a wick. If a single strand catches on the rotating chuck key holes or the drill bit flutes, the machine will scalp you by ripping hair out by the roots or pulling your face into the rotating chuck. The drill does not stop; your neck does.

Use a machine vice bolted to the table, or use heavy-duty G-clamps / toggle clamps to bolt the workpiece directly to the drill table. Position the clamps so your hands are at least 150 cms away from the bit. The cutting action of a drill bit creates rotational friction. If the bit bites into the metal and the workpiece is not clamped, the piece will instantly spin out of your grip at high speed, slashing your palms with its sharp edges. Worse, it can turn the workpiece into a flying projectile that can break bones or damage eyes. Clamping also leaves both your hands free to operate the feed levers smoothly.

If the table is not locked, the downward pressure you apply while drilling will force the table to slide abruptly down the column. This sudden drop removes all downward force, causes the bit to grab and snap, ruins the workpiece, and can cause your hands to smash into the spinning chuck as you lurch forward.

Place a scrap piece of softwood (pine or MDF) flat on the metal drill table. Clamp your metal workpiece on top of this wood, ensuring the wood extends beyond the exit point of the hole. When the drill bit breaks through the bottom of the metal, it exits aggressively and “grabs” the material. If the metal is directly on the cast-iron table, the bit will slam into the table surface, ruining the table and shattering the bit. The softwood allows the bit to cut gently into something sacrificial, prevents the metal from deforming downwards (burring), and protects the table.

Insert the drill bit fully into the chuck until it bottoms out, then pull it back out about 1-2mm and then tighten the chuck. If the chuck uses a key insert the key it in to the first hole and tighten; rotate the chuck 120 degrees to the next hole and tighten; rotate to next hole and tighten. Repeat the cycle twice to achieve maximum torque. Chuck has three independent jaws. Tightening only one hole tightens only two jaws, leaving the bit off-center (causing wobble and inaccurate holes). Using all three holes ensures concentric, equal pressure from all three jaws, gripping the bit's shank perfectly. This prevents the bit from slipping, spinning inside the chuck, or snapping under heavy load. Always remove the chuck key immediately after use. The instant you have tightened the last jaw hole, pull the key straight out of the chuck and place it in its designate storage location. This is the single most critical safety habit. If you leave the key in the chuck and switch the machine on, the spinning centrifugal force will eject the key at bullet-speed (over 100mph). It will fly across the workshop like a missile, capable of breaking ribs, shattering teeth, or penetrating an eye.

Place the sharp point of a centre punch exactly on the intersection of your measured crosshairs. Strike the punch sharply one time with a heavy hammer to create a small, conical dimple about 1-2mm deep. A drill bit's cutting edges are at the tip, but its very centre is a flat “chisel edge” that cannot cut. Without a dimple, this chisel edge will “walk” or skid across the smooth metal surface, ruining your precise layout. The punch mark gives the chisel edge a physical pit to sit in, guaranteeing that the bit starts exactly where you want it.

Select a small drill bit (about 3mm to 6mm, or 1/8“ to 1/4”). Drill a shallow hole through the centre punch mark first. Then, swap to your final large bit to enlarge that hole to the final size. The “chisel edge” on a large bit (over 12mm) is very wide and requires immense pressure to push through solid metal. Attempting this from scratch causes the bit to bounce, overheat, and dull instantly. A pilot hole removes the metal where the chisel edge sits, meaning the large bit's cutting corners now do all the work, requiring far less pressure and producing a perfectly round, accurate final hole.

Before you start drilling, squirt a few drops of proper dark sulphur-based thread-cutting oil directly into the centre punch mark. For aluminium only, you can use WD-40. Re-apply 2-3 drops every time you lift the bit to clear chips. Drilling metal generates enormous frictional heat (often over 400°C). Cutting fluid performs three jobs: it cools the bit to prevent it from losing its hardness (temper), it lubricates the cutting edges to reduce friction and torque, and it flushes chips away from the cutting zone. Water causes instant thermal shock and rust; it boils off and does not lubricate, leading to rapid bit destruction.

Adjust the belt position on the pulleys to achieve the correct RPM. As a rough rule: for a 3mm bit in steel, use ~2000 RPM; for a 10mm bit, use ~600 RPM; for a 20mm bit, use ~250 RPM. When in doubt, choose the slowest speed. “Surface Speed” (the velocity of the cutting edge against the metal) must remain constant. A large bit has a massive circumference; if it spins fast, the outer cutting edges travel at hundreds of metres per second, generating so much friction that they glow red-hot and instantly go blunt. Slow speeds allow the bit to “slice” rather than “rub.”

Use the feed lever to bring the rotating bit down until it just touches the metal. Then, apply gentle, steady downward pressure. Let the bit “bite” at its own pace; do not force or heave on the lever. You should see two even, curly chips forming. Forcing the drill down faster than it can cut causes the flutes (the spiral grooves) to clog with metal. When they clog, the bit stops cutting and starts rubbing, generating destructive heat. Letting the bit “cut” at its natural feed rate produces beautiful, continuous chips and maximises the bit's lifespan.

Drill into the metal for about 5mm (roughly ¼ inch). Without switching the drill off, pull the feed lever back up to completely withdraw the bit from the hole. Bring it back down and drill another 5mm deeper. Repeat. This “pecking” action breaks the long, continuous spiral of swarf (chips). Long stringy chips wrap around the bit like a spring, which can violently whip around and cut your hands, or clog the flutes entirely. By extracting, you physically break those strings into manageable pieces.

While the bit is lifted and the machine is running, use a stiff-bristled chip brush to sweep the hot, sharp swarf away from the hole and off the table into a scrap bin. Freshly cut metal chips are extremely sharp (like razor blades), often have microscopic burrs, and are hot enough to instantly burn your skin. Brushing keeps your hands safely away from the rotating spindle. Using your fingers almost guarantees deep lacerations or tiny metal splinters that infect easily.

At least every 10mm of depth, or whenever you hear the motor labouring, pull the feed lever up to full extension to completely clear the flutes of swarf, then apply fresh cutting fluid to the hole. Chips must travel up the spiral flutes to escape the hole. If the flutes become packed, the chips have nowhere to go; they get crushed at the bottom of the hole, causing extreme friction. Frequent lifting prevents the bit from seizing inside the hole, which would snap the bit flush with the metal (a nightmare to extract).

When the tip of the bit is just starting to poke through the underside of the metal, ease off the downward pressure to a mere feather-touch. Let the bit gently nibble its way through the final 1mm of material. As the bit exits the bottom, the cutting edges are no longer surrounded by metal on all sides. If you maintain heavy pressure, the bit will “grab” the remaining thin ring of metal, screw itself violently into the workpiece, and either snap the bit, shatter the workpiece, or violently yank it upwards off the table. Slow pressure ensures a clean, burr-free exit.

Hit the large red STOP button. Step back slightly and watch the chuck as it coasts down. Do not touch the workpiece, the chuck, or the bit until the rotation has completely ceased. A heavy drill chuck has significant rotational inertia and can coast for several seconds. Touching a still-spinning bit with a rag or your hand can snag and pull you in. Furthermore, trying to “brake” the chuck by grabbing it damages the internal spindle bearings. Letting it stop naturally is the safest mechanical practice.

Take a deburring tool (or a larger countersink bit) and gently twist it by hand (or at very low speed) around the top and bottom edges of the newly drilled hole to shave off the raised lip of metal. The drilling process extrudes a sharp, ragged “burr” (a raised ridge) around the entrance and exit of the hole. These burrs are razor-sharp and will slice your fingers when handling the part later. Deburring also ensures that if a bolt or screw is inserted, it will sit flush against the material without rocking.

Use a rag (wearing no gloves!) to grip the shank (the smooth top part) of the bit, not the cutting flutes and loosen the chuck. Wipe it down with a rag soaked in a little oil or solvent to remove all metal swarf and cutting fluid. The cutting edges of the drill bit can reach over 100°C; touching the flutes directly causes instant second-degree burns. Cleaning the bit immediately is crucial because dried cutting fluid turns into a sticky, acidic varnish that corrodes the high-speed steel and dulls the cutting edges over time.

Match the size (e.g., 10.0mm) engraved on the shank of the bit to the corresponding labelled hole of drill rack. Storing bits in their dedicated holder prevents them from rolling off the table and falling onto the concrete floor (which chips and dulls the cutting tip). It also ensures that the next user can instantly find the correct size, saving time and preventing people from using the wrong bit because they couldn't find the right one.

Using a stiff brush and a rag, sweep all metal chips off the drill table, out of the T-slots, and off the base plate. Wipe down the vertical column with an oily rag to prevent rust, and wipe any excess cutting fluid off the chuck. Metal chips left on the table will rust in the presence of cutting fluid, pitting the precision-ground cast-iron surface forever. Chips left in the T-slots will prevent you from clamping future workpieces flat. Finally, a clean machine allows you to visually inspect the chuck and belts for wear, ensuring the drill is safe and ready for the next user.