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How does the impact function work?

Shop for Cordless Impact Drivers

Anvil, hammer, motor in a cordless impact driver All cordless impact drivers have an impact function, which delivers a series of strong rotational bursts of force inside the tool, producing an extremely high level of torque when driving screws and drilling.

The impact function works through a hammer and anvil mechanism.

Motor, hammer, anvil, torque (turning force of impact driver) When driving screws into materials, the tool will encounter resistance. To overcome this resistance and continue driving in the screw, the tool must deliver more torque.
Spring pulls hammer back, screw encountering resistance, anvil disengages from hammer As resistance increases, a spring attached to the hammer retracts, pulling the hammer back away from the anvil.

While this is happening, the screwdriver bit continues to rotate.

Anvil's arms, screw overcoming resistance, hammer's lugs The spring then releases the hammer, which surges forward. Because the hammer is still rotating, its lugs (the projecting portions) strike the anvil’s arms as it turns.

These bursts or ‘impacts’ happen around 50 times per second, and deliver a strong rotational force to the screwdriver bit. This increases the torque (turning force) of the screwdriver bit on the screw, allowing it to overcome greater resistance.

Why is the impact function important to consider?

Pine All this torque makes some impact drivers a little difficult to control and great care should be taken when driving screws into soft materials such as pine.

Using a cordless impact driver with very soft materials can actually pose problems as between the hammer strikes there’s no torque applied and so the screwdriver bit can rotate backwards.

Driving a lag bolt with a cordless impact driver As a result, the high level of torque produced by cordless impact drivers makes them suited to heavy-duty jobs like driving long lag bolts!