Hammer drills and impact drivers have different applications — a hammer drill is used to to drill into hard surfaces like cement and concrete while an impact driver is used to install and remove bolts and screws. Both are very powerful tools but use different mechanisms of action. A hammer drill uses a hammer-like action on the drill bit to drive it into the hard surface. An impact driver, on the other hand, uses higher torque to screw in bolts.
A construction worker hammer drilling a brick wall
A hammer drill has more direct forward force – like a hammer. They can either have “cam-action” or “electro-pneumatic” hammering. Cam-action drills have a mechanism where the entire chuck and bit move forwards and backwards on the axis of rotation. Rotary hammers use electro-pneumatic hammering, where the piston and hammer do not touch, but where air pressure transfers the energy.
An impact driver exerts perpendicular pressure (torque), which is the same motion required to screw or unscrew fasteners. However, note that screwdrivers exert both torque and the forward motion to install the screw. In contrast, an impact driver only exerts torque and no longitudinal force to drive the screw forward. This is not a problem in most cases but it is good to be aware of this limitation of impact drivers, not least because it is a common misconception that impact drivers do apply that forward force.
There are two kinds of impact drivers - manual and motorized. A manual impact driver uses a heavy outer sleeve surrounding an inner core splined to it. Striking the outer sleeve with a hammer results in torque being applied to the screw. This is most effective for Philips screws (because they cam out), less effective for slot head screws and is not useful for most other types of screws. Motorized impact drivers are used to replace screwdrivers for greater speed and ease of use in applications where a large number of screws may need to be used e.g. manufacturing or construction.
An impact wrench is similar in function to an impact driver. Impact wrenches are motorized and use compressed air to apply the torque pressure. They are larger and use an anvil for a socket instead of a chuck for a hex bit that you find in an impact driver. While impact drivers tend to be used for screws, impact wrenches are more commonly used with nuts and bolts.
Hammer drills are useful for drilling through concrete, cement and other masonry. They are not useful for woodworkers, who tend to use regular drills.
Impact drivers are used for driving and removing screws in general construction and DIY projects. Impact wrenches may be used with nuts and bolts in applications such as auto repair.
A hammer drill is larger and heavier than a regular drill. They are more likely to be cordless than impact drills. Special drill bits need to be used with a hammer drill to withstand the strong pressure from the drill.
An impact drill is more compact and lightweight.
Both hammer drills and impact drivers are available at a wide range of prices. A good place to start looking is Amazon's best seller list:
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