The Really Wonderful Thing about Impact Drivers
When they first appeared years ago, impact drivers were all the rage 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 lumber, especially decking. American companies like Porter Cable grasped the idea and started competing with impact drivers offered by overseas companies. The idea of impact drivers was begun 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 mechanism 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 knocks the screwdriver bit around as if being repeatedly being whacked by a hammer. This action gives these woodworking tools considerable power that simply would not be possible if the exact same screwdriver bit were chucked up in an electric drill with the same size motor and battery. An extra 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 useful woodworking tools.
The first time I picked up an impact driver, a 12-volt Makita, I thought it appeared to be a toy. I then tried it out by driving a 3-inch deck screw into a 4 x 4 piece of fir. I was surprised as I watched (and felt) the tiny machine effortlessly drive the screw home, sinking the head under the face 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 ruin it. From that day forward, I have never been without one of these amazing devices 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 voltage 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 emergence of Lithium Ion technology and subsequent enhancements on that. In fact, a large part of the price tag 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 makers (but not all) have discovered that if they make all their tools run on one 18-volt Lithium Ion battery, they can sell more bare tool bodies while locking in their customer to their brand name. Regular buyers love this because they do not have to keep laying out hard-earned dollars for shelves full of different batteries and chargers but, instead, can just buy the bare machines 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 an advantage. You can demolish small screw heads and snap off 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 meet your requirements for most jobs, an 18 volt model is well worth the small increase in price.