Drill types explained
| Tool | What it does best | Not for |
|---|---|---|
| Drill/driver | Holes in wood, metal, plastic and drywall; driving screws with a clutch | Concrete and hard brick |
| Hammer drill | Everything a drill/driver does, plus small holes (up to about 1/2 in / 13 mm) in brick and occasional concrete | Frequent or large concrete holes |
| Impact driver | Long screws and lag bolts with high torque and little wrist strain | Precise holes (hex chuck, no clutch) |
| SDS-plus rotary hammer | Fast holes in concrete from 3/16 to 1-1/8 in (5–28 mm), light chiseling | Small screws, fine woodwork |
| SDS-max rotary hammer | Large holes and core bits in concrete, demolition | Light DIY tasks |
How the selector decides
The deciding factor is the hardest material and the largest hole. A hammer drill adds a rapid forward-and-back “hammering” motion to the rotation, which chips brick and soft masonry. Concrete is much harder: a rotary hammer uses an electro-pneumatic piston that delivers far more impact energy (measured in joules), so it drills concrete several times faster with less effort. That is why holes larger than about 1/2 in in concrete, or concrete drilling every week, point to an SDS-plus tool.
For wood and screws, torque is what matters. Small screws need 20–30 Nm (180–270 in-lb); 3 in deck screws and 1-1/2 in spade bits need 40–60 Nm; lag bolts, augers and large hole saws need 60–100 Nm or an impact driver. Brushless motors deliver more torque and runtime from the same battery and are worth it if you drill regularly.
12 V or 18/20 V?
12 V tools are compact and light, ideal for cabinets, furniture assembly and overhead work. 18 V (sold as 20 V max in the US – the same voltage, just a different way of labeling) tools have roughly 50–100% more torque and run hammer drills and rotary hammers properly. Pick the battery platform first: once you own batteries, buying more tools from the same system is much cheaper.
Battery capacity
Amp-hours (Ah) describe how long a battery lasts, not how strong the drill is. A 2 Ah battery keeps a drill light; 4–5 Ah batteries are better for hole saws, augers and rotary hammers. Professionals usually keep two batteries so one is always charging.
The drilling speed formula
Every material has a recommended cutting speed – how fast the edge of the bit should move across the material, in surface feet per minute (SFM). The spindle speed follows from the bit diameter:
RPM = (SFM × 3.82) ÷ bit diameter in inches or RPM = (cutting speed m/min × 1000) ÷ (π × diameter in mm)
Large bits must turn slowly and small bits fast. Too fast overheats and dulls the bit (you’ll see blue chips or smoke); too slow wastes time and can make the bit grab. Spade bits, Forstner bits and hole saws cut with their outer edge, so they need much lower speeds than twist bits of the same diameter.