When to Use Hammer Mode on a Drill (and When It Wrecks Things)

Hammer mode belongs on masonry and nothing else. Switch it on for brick, block, stone, mortar and concrete, and leave it firmly off for wood, metal, plasterboard, tile and anything plastic. The hammer symbol on your drill collar is not a "more power" button, it is a percussion mechanism that only helps when the material fails by being crushed rather than cut.

What hammer mode actually does

Inside a combi drill sit two ridged steel discs called ratchet plates. When you select the hammer symbol, those plates are allowed to click past each other as the chuck turns, so the whole spindle jolts forward and back thousands of times a minute while it spins. The result is a rapid tapping motion layered on top of normal rotation.

That tapping is what breaks masonry. Brick and concrete are brittle, so a tungsten carbide tip that is being hammered into the surface shatters tiny fragments loose, and the flutes of the bit spiral the dust back out of the hole. Without percussion, a masonry bit mostly rubs and polishes the hole, generating heat instead of progress.

Worth knowing: a combi drill's hammer action is light. It is measured in blows per minute, often 20,000 to 30,000, but each blow carries very little energy. An SDS rotary hammer uses a piston driving an air cushion instead, delivering far heavier blows at a lower rate. That is why a combi drill will get you a 6mm hole in brick without complaint but struggles badly with 16mm holes in structural concrete.

Materials where hammer mode is correct

• Brick. Standard clay brick takes hammer well. Engineering brick is much denser and slower going.
• Concrete block and breeze block. Lightweight aerated block barely needs it, and rotary only is often cleaner and less likely to blow out the back.
• Mortar joints. Soft and quick. Many fixings are better placed in the joint than the brick face anyway.
• Poured concrete. Fine for small anchors. Anything above roughly 10mm diameter or deeper than 60mm is SDS territory.
• Natural stone. Works, but reduce speed and expect the bit to wear fast.

Materials where hammer mode causes damage

This is where most of the harm gets done, usually by someone who left the collar set from the last job.

• Tile. Percussion cracks glaze almost instantly and can shatter a whole tile. Drill tile rotary only, slowly, with a spear point or diamond bit.
• Wood. Hammer gives you a ragged, oversized hole and blown out fibres on the exit side. It adds nothing, wood cuts rather than crushes.
• Metal. The tapping chips the cutting edges off an HSS bit and makes the tip skate across the surface before it bites.
• Plasterboard. Percussion tears the paper face and crumbles the gypsum, so your fixing has nothing left to grip.
• Plastic, acrylic and uPVC. Brittle materials crack, softer ones melt and grab. Slow rotary only.
• Old lime mortar and soft historic brick. Hammer can crumble the surrounding joint far wider than the hole you wanted.

Setting the drill up properly

Selecting hammer is only one of three settings that need to agree with each other, and getting the other two wrong is why people conclude their drill "isn't powerful enough".

1. Turn the collar to the hammer symbol. On most combi drills it sits past the highest clutch number and past the plain drill bit icon. Rotate it fully, not halfway, and give the collar a nudge while the chuck turns if it feels stuck between positions.
2. Select high gear. Masonry drilling wants speed, not torque, so gear 2 on a two speed drill. The percussion rate is tied to spindle speed, so a slow drill hammers less.
3. Fit a masonry bit. The tip will have a wider brazed carbide chisel that is visibly broader than the shaft. A twist bit in hammer mode will simply be destroyed.

Note that the clutch is bypassed in hammer mode on nearly every combi drill. That is deliberate, since a slipping clutch would make masonry drilling impossible, but it also means the tool will keep twisting hard if the bit binds. Use the side handle if the drill came with one.

Technique once you are drilling

Hold the drill square to the surface and apply firm, steady pressure. Firm means leaning your body weight in, not straining. If you are pushing so hard that the motor bogs down, you are just generating heat, and if you are barely touching it the bit will bounce and skate.

Start slow to establish the hole. Squeeze the trigger gently until the tip has cut a shallow dimple that stops it wandering, then bring it up to full speed. On a glazed or very smooth surface, a strip of masking tape or a small pilot dent with a nail punch stops the initial skate.

Withdraw the bit fully every 15 to 20mm of depth. That clears the dust out of the flutes, and clogged flutes are the single biggest reason a hole stops progressing. It also lets the carbide tip cool, which matters because overheated carbide loses hardness permanently.

If you hit something that will not give at all, stop. Hitting rebar in concrete or a very hard aggregate stone means more pressure will only cook your bit. Move the hole 30mm or so, or step up to an SDS drill with a bit rated to cut through steel.

Signs you should not be using a combi drill at all

A combi drill in hammer mode has real limits. If you have made no meaningful progress after 30 seconds in decent concrete, if the drill body is getting hot enough to be uncomfortable, or if you are drilling more than a handful of holes over 10mm, hire or buy an SDS. It is not a case of trying harder, the mechanism is simply the wrong one for the job and you will burn through masonry bits and possibly the drill trying to force it.