Combi drill, SDS or rotary hammer: the difference

Drill-driver and combi drill

A drill-driver drills into wood and metal and drives screws. A clutch with adjustable settings disengages the drive once the set torque is reached. That way you don’t sink a screw too deep or strip its head.

A combi drill adds a hammer setting. Two ridged discs ride over each other and push the chuck back and forth over a tiny distance, very quickly. The result is a high number of blows per minute, but little force in each blow.

Most of the hammering force comes from how hard you push. For a few wall-plug holes in brick or sand-lime brick, that’s enough. In concrete it’s slow, tiring and hard on the bit.

The rotary hammer

A rotary hammer has an electro-pneumatic hammer mechanism. A piston compresses a cushion of air, which drives a striker against the back of the bit. Each blow carries far more energy than in a combi drill, and you barely need to push.

Manufacturers state this impact energy in joules (J). The bit sits in an SDS chuck: it clicks in and can slide freely along its length. SDS-plus has a 10 mm shank and is used on light and medium rotary hammers. SDS-max has an 18 mm shank and is for heavy rotary hammers.

Many rotary hammers also have a hammer-only setting, without rotation. That lets you chisel, for example to remove tiles or cut a channel. Check the specifications to see whether a model has this setting.

Impact driver and impact wrench

An impact driver delivers short blows in the direction of rotation, not forwards. That lets it drive long, thick screws with little reaction force on your wrist. The bit holder is a 1/4-inch hex socket. It isn’t made for drilling into concrete.

An impact wrench works on the same principle but has a square drive for sockets. It is meant for nuts and bolts, such as wheel nuts and anchor bolts.

Which specifications to compare

On a drill-driver, the maximum torque in newton metres (Nm) tells you how much turning force there is. No-load speed shows how fast the chuck turns; there are often two gears. On a combi drill you’ll also find the number of blows per minute.

On a rotary hammer, impact energy in joules is the key figure. Manufacturers measure it by the EPTA procedure, a shared industry method. Also look at the weight including battery, especially if you often drill overhead.

Which bits you need

For wood you use wood bits with a centre point, for metal HSS bits. Masonry bits have a carbide tip and fit the ordinary chuck of a combi drill.

A rotary hammer with an SDS chuck takes SDS bits with grooves in the shank. SDS-plus bits don’t fit an SDS-max chuck, and vice versa. To drill wood or metal with a rotary hammer, you need an interchangeable chuck or an adapter.

Comparing on ToolRango

Many tools come as a bare tool without battery and charger, and as a kit with batteries, charger or case. Each version has its own EAN or order number. ToolRango compares per version, so you can see exactly which one you’re looking at.