Which drill bit should I use for aluminium?
Which drill bit should I use for aluminium?
A sharp HSS bit at high speed with a wax or paraffin lubricant — the problem is aluminium sticking to the bit, not hardness.
Aluminium is easy to cut and hard to cut well. It is soft and ductile, so it forms a built-up edge — material cold-welds to the cutting lip, which then rubs rather than cuts, generates heat and packs the flutes until the bit seizes. Lubrication is what prevents this, and the traditional choices are paraffin, wax or WD-40 rather than a heavy cutting oil, because the job is preventing adhesion rather than cooling. The other characteristic is the snatch at breakthrough: a positive-rake bit screws itself through the last thin section of soft metal, tearing the hole and spinning the work. Backing the workpiece and easing off at the end fixes it, and a step bit avoids it entirely.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Sharp HSS twist drill | Aluminium is soft, and a sharp standard bit cuts it easily and quickly. | Grabs badly at breakthrough because the material is so soft, and a blunt bit welds itself in. |
| HSS with a polished or bright finish | A smooth flute releases the swarf instead of letting it pack and weld. | Coated black-oxide bits are more prone to build-up. |
| Step bit | The best option for aluminium sheet, avoiding the snatch at breakthrough entirely. | Limited depth. |
| Bit ground with reduced rake | Reduces the self-feeding grab in thin sheet, which is the usual cause of a torn hole. | Needs a grinder and some skill. |
Technique that changes the outcome
- Run fast with a sharp bit and continuous light pressure
- Lubricate with paraffin, wax or a light penetrating oil, not heavy cutting paste
- Clear the swarf frequently; long strings wrap around the bit and the work
- Back thin sheet with scrap timber and ease off at breakthrough
What goes wrong
- A blunt bit, which welds aluminium to the flutes and seizes
- Drilling unsupported sheet by hand, which snatches and spins
- Letting swarf build up around the hole — it scratches the surface badly
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. |
| 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 aluminium?
- A sharp HSS bit at high speed with a wax or paraffin lubricant — the problem is aluminium sticking to the bit, not hardness.
- What should I avoid?
- A blunt bit, which welds aluminium to the flutes and seizes Drilling unsupported sheet by hand, which snatches and spins Letting swarf build up around the hole — it scratches the surface badly
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