Which drill bit should I use for wood?
Which drill bit should I use for wood?
A brad point bit for clean holes up to about 13 mm; an auger for depth and a Forstner for a flat bottom.
Wood tears rather than cuts, and every difference between these bits comes down to whether the fibres are severed before they are lifted. A twist drill's cutting lip lifts fibres and rips them at the rim, which is why entry and exit are ragged; a brad point severs the circumference with its spurs first. Exit tearout is a separate problem with one reliable answer, which is a sacrificial backing board clamped tight behind the work so there is no unsupported fibre to blow out. Speed should fall as diameter rises — a large Forstner run fast burns the timber and the bit before it cuts.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Brad point bit | The centre spur stops it wandering and the outer spurs cut the fibres before the flutes lift them, so entry is clean. | Clogs in deep holes and is easily blunted by a hidden nail. |
| Standard HSS twist drill | Cheap, available in every size, and perfectly adequate for rough work and pilot holes. | Wanders on start and tears the fibres on entry and exit. |
| Auger bit | A screw point pulls it through, and the deep single flute clears chips from a long hole. | Self-feeding means it grabs; needs low speed and a firm grip or a brace. |
| Forstner bit | Flat-bottomed, can be started at an angle or on an edge, and cuts overlapping holes cleanly. | Generates a lot of heat, needs a drill press for accuracy, and is slow. |
Technique that changes the outcome
- Clamp a sacrificial board behind the work to prevent breakout
- Mark the centre with an awl so the spur has something to sit in
- Slow down as the bit gets bigger; large bits want a few hundred rpm, not a few thousand
- Withdraw periodically on deep holes to clear the chips
What goes wrong
- Drilling into old timber without checking for nails and screws
- Running a spade or auger bit at full speed, where it grabs and twists the work
Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.
Other drill bit questions
| For | Use |
|---|---|
| Tile | A spear-point carbide or diamond bit in rotary mode only — hammer action shatters tile, every time. |
| Metal | An HSS twist drill, ideally with a 135° split point, run slowly with firm pressure and cutting fluid. |
| Concrete | An SDS-plus carbide bit in a rotary hammer — a normal hammer drill will get there eventually and blunt several bits doing it. |
| Masonry | A carbide-tipped masonry bit in hammer mode for brick and block; step up to an SDS rotary hammer above about 10 mm. |
| Porcelain tile | A diamond core bit, cooled with water, at low speed — carbide spear points do not cut porcelain. |
| Stainless steel | A cobalt bit at low speed with heavy constant pressure and cutting fluid — and never let it stop cutting. |
| Plasterboard (drywall) | Almost none — an ordinary HSS or brad point bit in rotary mode, and the real question is which fixing goes in the hole. |
| Glass | A spear-point carbide or a diamond bit, run slowly under water — and toughened glass cannot be drilled at all. |
| Plastic | An HSS bit ground to a shallower rake, or a plastic-specific bit, at low speed with a backing board — acrylic especially will crack. |
| Hardened steel | Solid carbide in a rigid setup, or soften the spot first — HSS and cobalt cannot cut anything much above 50 HRC. |
| Aluminium | A sharp HSS bit at high speed with a wax or paraffin lubricant — the problem is aluminium sticking to the bit, not hardness. |
| Large holes in wood | Spade for speed and roughness, auger for depth, Forstner for a clean flat bottom, hole saw for big diameters in thin stock. |
Common questions
- Which drill bit should I use for wood?
- A brad point bit for clean holes up to about 13 mm; an auger for depth and a Forstner for a flat bottom.
- What should I avoid?
- Drilling into old timber without checking for nails and screws Running a spade or auger bit at full speed, where it grabs and twists the work
Related pages
- Which drill bit should I use for tile? A spear-point carbide or diamond bit in rotary mode only — hammer action shatters tile, every time.
- Which drill bit should I use for metal? An HSS twist drill, ideally with a 135° split point, run slowly with firm pressure and cutting fluid.
- Which drill bit should I use for concrete? An SDS-plus carbide bit in a rotary hammer — a normal hammer drill will get there eventually and blunt several bits doing it.
- Which drill bit should I use for masonry? A carbide-tipped masonry bit in hammer mode for brick and block; step up to an SDS rotary hammer above about 10 mm.
- Which drill bit should I use for porcelain tile? A diamond core bit, cooled with water, at low speed — carbide spear points do not cut porcelain.
- Which drill bit should I use for stainless steel? A cobalt bit at low speed with heavy constant pressure and cutting fluid — and never let it stop cutting.
- Which drill bit should I use for plasterboard? Almost none — an ordinary HSS or brad point bit in rotary mode, and the real question is which fixing goes in the hole.
- Which drill bit should I use for glass? A spear-point carbide or a diamond bit, run slowly under water — and toughened glass cannot be drilled at all.
- Which drill bit should I use for plastic? An HSS bit ground to a shallower rake, or a plastic-specific bit, at low speed with a backing board — acrylic especially will crack.
- Which drill bit will go through hardened steel? Solid carbide in a rigid setup, or soften the spot first — HSS and cobalt cannot cut anything much above 50 HRC.
- Which glue works on wood? Glue and adhesive
- Which circular saw blade for wood? Blade
- Which screw and pilot hole should I use for wood? Screw
Sources
- Typical range compiled from manufacturer specifications — At One Place