Which bit should I use for large holes in wood?
Which bit should I use for 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.
The four tools solve different problems and swapping them produces poor results. Spade and auger bits remove the whole hole as chips and are meant for structural and services work where appearance does not matter; Forstner bits shear the rim and pare the bottom, which is why they leave a flat base and clean walls. Hole saws only cut the annulus, which makes them efficient in thin sheet and awkward in thick timber because the plug binds — drilling from both faces, or clearing the plug with a chisel through the pilot hole, is the usual fix. Whatever the bit, torque rises steeply with diameter, so a large bit in a powerful drill can wrench the tool out of your hands: use the side handle.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Spade (flat) bit | Cheapest and fastest way to put a 25 mm hole through a joist for a cable. | Ragged entry and exit, wanders, and grabs hard if it is fed too fast. |
| Auger bit | Self-feeding screw point and a deep flute that clears chips, so it goes deep without clogging. | Pulls itself in aggressively; needs low speed and a firm grip. |
| Forstner bit | Flat-bottomed, clean-walled, and can overlap holes or cut on the edge of a board — the choice for hinge cups. | Slow, hot and best used in a drill press. |
| Hole saw | Large diameters in thin material at low cost, and the only practical option above about 50 mm. | Cuts only a ring, jams on the plug, and burns in thick or resinous timber. |
Technique that changes the outcome
- Use the side handle on anything above about 20 mm — the reaction torque is serious
- Reduce speed as diameter increases
- Back the workpiece, or drill until the point emerges and finish from the other side
- For hole saws, drill halfway from each face to avoid a jammed plug and a torn exit
What goes wrong
- Drilling through joists without checking the permitted zones and hole sizes
- Running a hole saw at full speed, which burns the timber and the teeth
- Holding small work by hand with a large bit
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. |
| Wood | A brad point bit for clean holes up to about 13 mm; an auger for depth and a Forstner for a flat bottom. |
| 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. |
Common questions
- Which bit should I use for 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.
- What should I avoid?
- Drilling through joists without checking the permitted zones and hole sizes Running a hole saw at full speed, which burns the timber and the teeth Holding small work by hand with a large bit
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 wood? A brad point bit for clean holes up to about 13 mm; an auger for depth and a Forstner for a flat bottom.
- 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.
Sources
- Typical range compiled from manufacturer specifications — At One Place