Drill Bits & Sets

Drill bits and sets create or enlarge holes in specific materials using a matched tool, speed, feed and cutting fluid. This collection can include HSS jobber and blacksmith bits, cobalt-alloy metal bits, titanium-nitride-coated bits, hex-shank and impact-compatible sets, step drills, hole saws, multi-material bits and combined drill-and-tap tools. A bit that physically fits the chuck is not automatically suitable for the material or machine.

Select by finished hole size, workpiece material and thickness, bit geometry, shank, overall/flute length, tool speed range and whether a pilot, arbor or cutting lubricant is required. Cobalt HSS helps retain hardness in tougher metals; a TiN coating reduces friction only while intact and is not the same as solid cobalt. Large blacksmith bits need adequate chuck capacity and low-speed torque, while hole saws require the correct arbor and pilot.

Inspect the bit for chips, cracks, bending, worn cutting lips and damaged shank. Confirm chuck and arbor retention, remove the battery or isolate the machine for fitting, and use guards where provided. Clamp the work securely—never hold sheet metal by hand. Wear eye protection, tie back hair and avoid loose clothing or gloves near rotating parts. A grabbing drill can spin the workpiece or wrench the tool violently.

Mark and centre the hole, use a pilot where appropriate and keep the tool square. Apply a speed suited to bit diameter and material: larger diameters normally require lower rpm. Feed enough to form controlled chips without rubbing, clear swarf with power stopped and a brush, and use compatible cutting fluid. Do not touch chips or the bit immediately; both may be sharp and hot.

Before drilling a vehicle, check behind the surface for wiring, fuel and brake lines, airbags, tanks, batteries and structural components. Protect against sparks and conductive swarf. Deburr the completed hole, treat exposed metal against corrosion and clean every chip from tyres, seats, electrical equipment and moving assemblies. Replace rather than force a dull or damaged bit, and use a purpose-made tapping or hole-forming process when thread quality is safety-critical.

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A drill bit cuts correctly only when geometry, speed and feed agree

The cutting lips shear material, the chisel edge pushes at the centre and flutes evacuate chips. Excess speed creates heat and softens the edge; insufficient feed makes it rub. Too much feed overloads the lips, machine and workholding.

Diameter changes cutting speed at the outer edge, so a larger bit normally turns more slowly in the same material.

Bit families serve different materials and hole shapes

Bit type	Typical purpose	Strength	Main limit
HSS jobber	General metal, plastic and wood where suitable.	Versatile standard-length twist geometry.	Loses hardness if overheated.
Cobalt-alloy HSS	Stainless and tougher heat-producing metals.	Improved hot hardness.	Can be less forgiving of flex/impact.
TiN-coated HSS	Reduced friction/wear in compatible cutting.	Hard low-friction surface.	Sharpening removes coating at the edge.
Blacksmith/reduced-shank bit	Large hole with smaller chuck compatibility.	Large diameter without full-size shank.	Machine may lack low-speed torque/rigidity.
Step drill	Several clean diameters in thin sheet.	Low grabbing and good deburring.	Limited material thickness/depth.
Hole saw	Large circular cut with minimal material removal.	Efficient large diameter.	Needs arbor, pilot, clearance and chip control.
Drill/tap combination	Drill and form thread in one supported operation.	Fast alignment in suitable thin material.	Needs exact pitch, thickness and reversing control.
Multi-material bit	Named masonry/wood/metal combinations.	Useful where substrate is known and supported.	No universal optimum for every layer.

Material drives point geometry and cutting conditions

Workpiece	Useful approach	Avoid	Warning sign
Mild steel	Sharp HSS, suitable fluid, steady feed.	High-speed rubbing.	Blue chips/bit and squeal.
Stainless steel	Rigid setup, cobalt HSS, low speed and positive feed.	Pausing while edge rubs/work-hardens.	Glazed hard spot and no chip.
Aluminium	Sharp open flutes and compatible lubricant.	Built-up edge and clogged flutes.	Material welded to cutting lip.
Thin sheet	Step drill or supported sharp bit with backing.	Hand-holding the sheet.	Snagging and triangular hole.
Plastic	Low heat, suitable rake and backing.	Melting/cracking from pressure.	Stringing, white stress marks.
Masonry/tile	Correct dedicated bit and impact setting.	Using hammer mode on unsupported tile/glass.	Cracking or polished tip.

HSS, cobalt and coatings

High-speed steel combines toughness and hot hardness for cutting. Cobalt-alloy grades retain hardness at higher temperature but still need correct speed and lubrication. A surface coating can reduce friction and wear, but it cannot compensate for poor geometry or a soft substrate.

Do not identify metallurgy by colour alone. Oxide, coating and temper discolouration can look similar.

Shank and chuck compatibility

Round shanks need full clean jaw engagement. Hex shanks improve quick-change retention but may be made for drill/drivers, impact drivers or both according to the bit rating. Reduced shanks let a small chuck hold a large bit but do not increase machine capacity.

Check chuck maximum diameter, spindle taper, minimum rpm and side handle. Tighten at every keyed position where the chuck instructions require it.

Impact-compatible drill bits have boundaries

A hex-shank set may tolerate an impact driver's torsional pulses, but the cutting tip still needs appropriate speed, feed and material. Impact action can chip brittle cobalt edges, enlarge holes or strip a combined tap.

Use the mode and tool specified by the bit maker. Do not confuse an impact driver with a masonry hammer drill.

Workholding prevents the most violent failures

Clamp the work to a bench or drill-press table and add backing beneath thin sheet. Position clamps clear of the bit path. A drill catching at breakthrough can spin sheet metal into a sharp blade.

For handheld work, brace the side handle and stand so a stall will not trap wrists. Never lock the trigger on where rapid release is needed.

Marking, centre punching and pilot holes

Measure twice, use a centre punch suitable for the surface and begin with a short rigid pilot when the final bit needs guidance. An oversized pilot can leave the final chisel edge unsupported and make cutting chatter.

Step drilling through several twist-bit sizes is not always necessary; follow the geometry guidance for the final bit and machine.

Speed, feed and chip evidence

Observation	Likely condition	Adjustment	Risk if continued
No chip, polished surface	Dull edge, low feed or work hardening.	Stop, sharpen/replace and reset.	Heat and hardened spot.
Blue bit/chips	Excess heat/speed or poor fluid.	Reduce rpm, improve cutting/lubrication.	Lost hardness.
Long tangled swarf	Ductile material and poor chip break.	Use peck/geometry as supported.	Entanglement and surface damage.
Chatter/triangular hole	Flex, poor centring or thin sheet.	Improve support; use step drill.	Oversize hole and broken edge.
Sudden grab at exit	Feed too high at breakthrough.	Support backing and reduce pressure near exit.	Spun work or wrist injury.

Cutting fluid and temperature

Use a fluid compatible with workpiece, bit, subsequent paint/welding and workplace controls. Apply enough at the cutting zone without aerosolising it. Some plastics and composites require dry methods or extraction instead.

Stop to cool naturally. Quenching an overheated bit can cause cracking or does not restore lost temper.

Step drills in sheet metal

Mark the required step, clamp the sheet and stop before the next diameter enters. The next step can lightly deburr if the tool is designed for it, but excessive pressure makes a countersink or thin edge.

Check the opposite side for burrs and treat exposed metal against corrosion.

Hole saws, arbors and pilot drills

Match saw diameter, arbor thread/pins and pilot to the material. Secure drive pins fully and use a drill with sufficient low-speed torque and side handle. Large saws produce strong reaction and a hot slug.

Clear chips with power isolated. Confirm space behind the work for pilot and slug; protect hidden components.

Combined drill-and-tap tools

These tools suit specified material thickness because the drill portion must pass through before the tap engages. Use the exact thread pitch, tapping speed and lubricant, keep square and reverse cleanly to break/remove chips.

Do not use them for deep blind holes or safety-critical threads unless the engineering procedure approves the resulting engagement and tolerance.

Sharpening and replacement

Restore geometry, not just a shiny edge

Twist-drill lips must be equal in length and angle with correct relief; an off-centre point cuts oversize. Sharpen with guarded equipment and cooling discipline, or use a professional sharpener. Coated bits lose edge coating when ground.

Retire structurally damaged tools

Replace cracked, badly overheated, bent or severely chipped tools. Never straighten a hardened drill bit for reuse.

Depth stops and breakthrough protection

Set a collar, machine stop or physical spacer when the hole must not reach hidden equipment. Verify from the bit tip and account for the full conical point, not only flute length. A tape flag can move and is only a visual guide.

Reduce feed as the point breaks through and support the exit face to limit burr, delamination and grabbing.

Vehicle drilling hazards

Inspect both sides for fuel/brake lines, looms, airbags, batteries, tanks and structural reinforcements. Isolate electrical systems where conductive swarf could short them. Shield glass and interiors from hot chips.

Do not drill chassis, restraint, wheel, brake or high-voltage structures without approved repair data. A neat hole can still make a component unsafe or illegal.

PPE and swarf control

Wear impact eye protection and manage noise; use face/respiratory controls for the material risk. Do not wear loose gloves near rotating spindles. Stop rotation before brushing chips and never clear swarf with fingers or compressed air toward others.

Hot spirals can cut shoes and ignite debris. Maintain a clean fire-controlled work area.

Practical drill-bit-and-set FAQs

Q: Is cobalt HSS only a coating?
A: No. Cobalt is alloyed into the HSS; TiN is a surface coating.

Q: Can a large bit run at the same rpm as a small one?
A: Usually no. Larger diameter needs lower rpm for the same cutting speed.

Q: Why will a bit not cut stainless?
A: It may be dull or rubbing has work-hardened the surface; use rigid low-speed positive-feed technique.

Q: Can sheet metal be held by hand?
A: No. Clamp it because a grabbing bit can spin it violently.

Q: Does a hex shank mean impact-rated?
A: No. Confirm the bit's tool and mode rating.

Q: What is a reduced-shank bit?
A: Its cutting diameter exceeds the shank, allowing a smaller chuck, but machine capacity still limits use.

Q: When is a step drill useful?
A: For clean multiple diameters in suitable thin sheet with controlled breakthrough.

Q: Can any arbor fit a hole saw?
A: No. Match thread, drive pins, pilot and diameter range.

Q: Should cutting fluid always be used?
A: Use the fluid or dry method specified for bit, material and later process.

Q: Can a blue overheated bit be quenched and reused?
A: Cooling does not restore lost hardness; inspect and replace/sharpen as appropriate.

Q: Are drill-and-tap bits suitable for deep holes?
A: They are normally intended for supported thicknesses where the drill clears before tapping.

Q: How should swarf be removed?
A: Stop and isolate rotation, then use a brush or chip tool—never bare fingers.

Q: What completes a drilled vehicle hole?
A: Deburr, remove all swarf, protect bare metal and verify no hidden system was damaged.