When they first came out years ago, impact drivers were very popular in Japan but it took a while for Americans to realize what a terrific advantage impact drivers have over an electric drill when it comes to driving long screws into wood, especially decking. American companies like Porter Cable caught on to the idea and started competing with impact drivers offered by overseas companies. The idea for impact drivers was born long ago with the inventions of (1) the impact wrench, used in every automotive garage, and (2) the hammer drill used to power masonry bits into concrete and other extremely hard materials.
The technology that allows them to do this is sometimes referred to as “hammer and anvil” meaning that, unlike the simple twisting action of an electric drill, the impact driver literally “pounds” the screwdriver bit around as if being repeatedly being hit by a hammer. This action gives these woodworking tools tremendous power that simply would not be possible if the same screwdriver bit were chucked up in an electric drill with the same size motor and battery. An additional advantage is that there are hex shank drill bits available so that your impact driver can double as a quick-change cordless drill thus becoming one of your most versatile woodworking tools.
The first time I picked up an impact driver, a 12-volt Makita, I thought it looked, to me, like a toy. I then tried it out by driving a 3-inch deck screw into a 4″ x 4″ piece of fir. I was amazed as I watched (and felt) the tiny machine effortlessly drive the screw home, sinking the head below the surface of the wood. I had to remember to keep a lot of hand pressure against the tool so that the screw driver bit did not pop out of the screw head and strip it. From that moment forward, I have never been without one of these amazing machines at my side.
Over the years, these drivers have been improved to the point of near perfection and this includes the batteries that power them. Battery size has grown from 9.6 volts to 18 volts and more. More than that, battery life has been greatly extended from what it was with the advent of Lithium Ion technology and subsequent improvements on that. In fact, a significant part of the cost of any impact driver, whether it comes from Makita Tools, Bosch or DeWalt is the battery or batteries that come with it.
You may have noticed that most manufacturers of cordless woodworking tools have started selling so-called “bare tool bodies” meaning that they come with no battery or charger included and a greatly reduced price tag. The reason for this is that most manufacturers (but not all) have discovered that if they make all their tools run on the same 18-volt Lithium Ion battery, they can sell more bare tool bodies while locking in their customers to their brand. End users love this because they do not have to keep laying out hard-earned money for shelves full of different batteries and chargers but, rather can just buy the bare woodworking tools that share the same battery.
Several manufacturers like Makita Tools have included two or more speed ranges in their impact drivers. Sometimes, too much power is not always a good thing. You can destroy small screw heads and break screw shafts. The more power used, the less battery life. Just because you have a 400 HP motor under the hood of your car does not mean that you drive around town with the accelerator pedal to the floor.
While a 12 or 14.4 volt impact driver will suffice for most jobs, an 18 volt model is well worth the small increase in price.