Summary

Choosing the wrong drill bit is the most common cause of broken tiles, blunted bits, damaged workpieces, and overheated drills. This guide provides a quick-reference cross-reference for all common building materials and the correct bit type, drill mode, and technique.

For tradespeople, having the right bit set and understanding how to use each type correctly is a daily requirement. The principles are not complex, but the details matter — particularly for tiles (where a wrong technique in the first second destroys an expensive tile), hardened steel (where an ordinary HSS bit achieves nothing), and masonry in unknown condition (where hitting a hard inclusion with the wrong bit causes a violent kickback).

Quick Reference Table — Bit by Material

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Material Bit Type Drill Mode Speed Notes
Softwood HSS or wood spade/brad-point Drill (no hammer) Medium–high Sharp bit, steady feed
Hardwood Brad-point or HSS Drill (no hammer) Medium Slow feed, sharp bit, clear chips
MDF/chipboard HSS Drill (no hammer) Medium Fine dust — mask required
Plywood HSS or brad-point Drill (no hammer) Medium Backing board prevents breakout
Mild steel HSS-G (ground) Drill (no hammer) Slow–medium Cutting fluid (WD40), firm steady pressure
Stainless steel HSS-Co (cobalt) Drill (no hammer) Very slow Cutting oil essential, no dwelling
Cast iron HSS or carbide Drill (no hammer) Slow No cutting fluid (CI is self-lubricating)
Hardened steel Carbide-tipped or CBN Drill (no hammer) Very slow Often need specialist equipment
Brick (hand drill) Masonry (carbide-tipped) Drill or hammer Medium Hammer assists, reduce pressure in soft brick
Concrete block (lightweight) Masonry (carbide) Hammer Medium SDS-plus recommended for >8mm holes
Dense concrete SDS-plus masonry bit Hammer drill Medium Must use SDS chuck — not round shank in SDS
Engineering brick SDS-plus masonry Hammer drill Medium–slow Hard facing can deflect bit — start carefully
Natural stone (limestone) Masonry or diamond Hammer or drill Medium Limestone fractures — care with hammer mode
Granite Diamond core Drill (no hammer) Slow Water coolant required
Ceramic tile Diamond (or carbide point) Drill (no hammer) Very slow No hammer, water coolant or tile cutting tape
Porcelain tile Diamond (sintered) Drill (no hammer) Very slow Porcelain is very hard — quality diamond bit only
Glass Diamond core or carbide Drill (no hammer) Very slow Water coolant, no pressure — let the bit do the work
Plasterboard HSS or multi-purpose Drill (no hammer) Medium Low pressure — plasterboard is soft
Cast/lead pipe HSS Drill (no hammer) Slow Lead is self-lubricating, no coolant needed
UPVC pipe/sheet HSS Drill (no hammer) Slow–medium No hammer, heat buildup — clear chips frequently
Copper HSS Drill (no hammer) Slow Cutting fluid, back off pressure at breakthrough

Bit Types Explained

HSS (High-Speed Steel)

The standard general-purpose metal drill bit. Available in several grades:

  • HSS-R (rolled): Lowest quality — for occasional use in soft metals and wood
  • HSS-G (ground): Better finish and accuracy — for regular use in mild steel and hard wood
  • HSS-Co (cobalt): 5–8% cobalt addition makes the bit heat-resistant — for stainless steel, hardened metals, and demanding applications

Colour indicator (approximate): Bright silver = HSS-R. Dull grey = HSS-G. Gold-coloured = cobalt-treated or titanium nitride coated (increases surface hardness).

Grinding angle: The standard included angle for HSS bits is 118° (for general use in most metals and wood). For harder materials (stainless, hard alloys): 135° split point reduces walk at the start of the hole and requires less pressure.

Masonry Bits

Masonry bits have a tungsten carbide tip brazed to a steel shank. The carbide tip is harder than masonry materials and gradually chips away the material at the bottom of the hole with the hammering action.

Grades:

  • Standard masonry bit — for soft brick, block, and plaster
  • High-duty masonry bit (thicker shank, better tip quality) — for dense concrete and aggregate
  • SDS-plus masonry bit — square groove on shank for SDS chuck, transmits impact force more efficiently

When masonry bits fail prematurely: Hitting a rebar or a hard inclusion (flint, aggregate piece) in concrete will instantly damage or destroy the carbide tip. Listen for a change in drilling sound — a clink or sudden resistance may indicate a hard inclusion. Reduce pressure and try to drill around it.

SDS-Plus and SDS-Max

SDS (Slotted Drive System) shanks are designed for hammer drill (rotary hammer) chucks. The slots in the shank allow the bit to slide axially within the chuck, transmitting impact directly from the hammer mechanism rather than through the chuck jaws. This is dramatically more efficient for concrete drilling than using a standard round-shank bit in an SDS chuck.

  • SDS-Plus: Standard domestic and light professional rotary hammer. Shank diameter 10mm with specific slot pattern. Maximum practical bit size approximately 26mm diameter in concrete
  • SDS-Max: Heavier professional rotary hammer. Larger shank, higher impact energy. For large holes (>26mm) in hard concrete

Never use SDS-plus bits in a standard keyless chuck: The groove pattern will not engage and the bit may slip or be damaged.

Diamond Core Bits

Diamond core bits use industrial diamond particles impregnated into a sintered metal matrix at the cutting edge. The diamonds abrade rather than cut the material — slow speed and water coolant are essential to:

  1. Prevent the diamonds from glazing over (becoming polished and losing cutting ability)
  2. Prevent heat build-up that would damage the bond between diamonds and matrix
  3. Wash away the abrasive slurry generated

Types:

  • Diamond-tipped drill bit (small): For tiles, glass up to approximately 50mm diameter. Hollow cylinder with diamond at the cutting edge
  • Diamond core barrel (large): For drilling through masonry walls — 50mm to 300mm+ diameter. Requires a dedicated core drill (not a standard drill)
  • Segmented diamond blade (angle grinder): For cutting tile and stone — not drilling

Running diamond bits dry: Will rapidly destroy the bit and potentially create dangerous heat in the workpiece (particularly glass). Always use water coolant or tile drilling gel.

Spade (Flat) Bits

Wide, flat wood bits for fast rough holes in timber. Not appropriate for clean joinery — use a brad-point for clean holes. Available in 6mm to 38mm diameter.

Technique: Entry and exit must be controlled — the spade bit will tear out the wood at exit. Drill through until the tip just protrudes, then drill from the other side to meet it, preventing tearout on the exit face.

Forstner Bits

Precise, clean holes in wood with a flat base — ideal for concealed hinges, shelf pin holes, and any application where a clean flat-bottomed hole is needed. Must be used in a drill press or very steady hand drill. Not for masonry.

Hole Saws

Circular toothed cylinders for cutting large holes (typically 20–200mm diameter) in wood, plasterboard, and sometimes metal. Most hole saws use a central pilot bit to locate the cut, leaving a round plug inside the saw.

For plasterboard: Any bi-metal hole saw or purpose-made plasterboard hole saw. Clean holes for downlights, spotlights, and socket back boxes.

For metal: Bi-metal (HSS-Co teeth in flexible steel body). Cutting fluid essential for steel.

Technique Notes by Material

Tiling Technique (Critical — Get This Wrong and the Tile is Lost)

  1. Mark the hole position with a marker pen
  2. Apply a cross of masking tape over the tile at the hole location — prevents the bit from skating on the glazed surface during start-up
  3. Select a diamond-tipped bit of appropriate size. Never use a masonry bit on tiles — it will crack them
  4. No hammer action — never use hammer mode on tiles or glass
  5. Apply gentle pressure and start at very slow speed — let the bit penetrate the surface
  6. Once started (approximately 2mm deep), increase speed slightly but maintain gentle pressure
  7. Apply water coolant continuously or use tile drilling gel (a thick coolant gel applied to the tile surface)
  8. At breakthrough, reduce pressure immediately — the bit should just fall through without the tile cracking
  9. For large holes in tiles (50mm+): use a diamond core bit with a guide that registers on the tile surface and prevents skating

Drilling Steel Technique

  1. Centre-punch the hole location — creates a small indent to prevent the bit skating at start-up
  2. Start with a small pilot hole (3–4mm) — easier to centre accurately
  3. Step up in sizes to reach the finished diameter — less force, better results
  4. Apply cutting fluid (WD40, cutting oil, or dedicated metalworking coolant) throughout
  5. Firm, steady downward pressure — the bit should be cutting, not spinning in place
  6. Clear chips regularly — pull the bit out briefly to allow chips to clear and coolant to reach the tip
  7. If the bit heats up rapidly and cutting slows: you may be dwelling (spinning without cutting). Increase pressure. If the bit is blunt, replace it

Drilling Stainless Steel

Stainless steel work-hardens if the cutting speed is too high or if the bit dwells without cutting. Once work-hardened, the surface becomes extremely hard and will rapidly blunt ordinary HSS bits.

  • Use cobalt HSS bits (HSS-Co, 8% cobalt)

  • Very slow speed — half the speed used for mild steel

  • Firm pressure — must cut continuously, never dwell

  • Cutting oil — essential

  • If the bit stops cutting but the surface looks intact: the steel has work-hardened. A new location or a carbide bit is needed

  • expansion materials — Thermal expansion coefficients by material

  • tile cutting — Tile cutting tools and techniques

  • data cabling — Drilling through walls for cable runs

  • first fix second fix — Drilling for fixings in first and second fix carpentry