Back in 2016, while we were restoring an 1880s Mississippi River skiff, we needed a second cordless drill/driver, so we could have one to drill pilot holes, and the other to drive screws. When I went to purchase the second drill/driver, I found a combo package from Kobalt that included a 24-volt impact driver. We were not sure exactly what it was used for, but when we found it could drive screws even better than the drill/driver, we were extremely pleased, and it has driven countless screws in the four years since then.
With the drill/driver we had been using to drive silicon-bronze screws into the skiff’s cypress, the driver bits tended to “cam out”—that is, strip out—and damage the soft bronze Frearson slots with disturbing regularity and at other times shear the screw’s shaft. We tried a variety of fixes, like waxing or greasing the screw, with poor results. Sometimes the drill drove screws right through a plank. Setting the clutch helped a bit, but variations in wood grain and density made for unpredictable results.
The impact driver spins the bit first; then when the resistance increases, a rotating weight inside the driver slips, stores energy in a spring, and then releases, creating an impact that rotates the driver bit and pushes it forward. The forward motion into the screw head greatly reduces the tendency of the bit to cam out of the screw slots. The mechanism gives the impact drive much more force, but doesn’t transfer any torque to the user, so it is easier to use for long periods of use. Impact drivers are loud when they switch to the impact mode, so be prepared for that and wear hearing protection.
While the impact driver has lots of power, more than enough to shear screws, the variable-speed trigger provides the operator with very good control for the depth of the screw. Our impact driver had the finesse to drive #6 and #8 marine stainless screws on 1/4″ (6mm) planks, where exact depth setting was critical. The impact driver also had the powerful yet controlled torque we needed when using long temporary screws with fender washers to pull plank sections together for scarfing or to set Dutchman patches tight for gluing.
Recently we bought the DeWalt’s DCF787 20V impact driver, which is lighter and smaller than the Kobalt. Both tools have brushless motors, which are more efficient and use less power than brush-equipped motors, so our batteries last almost twice as long. Skipper likes the smaller DeWalt which weighs in at 2.1 lbs; it has nice balance and weight and it will fit into small spaces. The LED light on the head of the driver is also handy in remote corners. The DeWalt driver has a no-load speed of up to 2,800 rpm and drives screws with up to 3,200 impacts per minute and a maximum torque of 1,500 inch-pounds. It is a “smart tool” that senses reduced loads on soft materials and decreases demand on the motor, and provides only the required power.
The Kobalt has a “finish” function that shuts down the driver after the impact mode has been activated (for one second in order to prevent overdriving the screw), but we found this reduces our control of the tool. The Kobalt has a no-load speed up to 2,700 rpm and can deliver 3,500 impacts per minute and 1,800 inch-pounds.
Impact drivers are useful additions to the tool kit for boatbuilding, woodworking, and household jobs. They offer power and control and, by stripping fewer screws, they’ll reduce the need to resort to salty language.
Audrey and Kent Lewis mess about with their fleet of small boats in the shoal waters of Northwest Florida. Their adventure log can be found at Small Boat Restoration.
I had never used an impact driver until I had edited this article and bought one. Actually I thought I’d bought one, but it was just a driver that looked like an impact driver but without the impact. It was a good complement to my drill driver, so I didn’t send it back. Paying a little more attention to my shopping, I did buy an impact driver, tool only, that used the 12-volt batteries and charger that I have for my Milwaukee drill/driver. The Milwaukee 12-volt impact driver won’t provide the power that the Lewises have with their brushless 20- and 24-volt impact drivers. They put the power to good use driving screws through 500 square feet of 2×6 decking along their waterfront bulkhead, but I’m content having a lighter-duty impact driver. A brushed-motor version is much less expensive, and while it isn’t said to be as efficient or as long lasting as a brushless motor, my first cordless tool, a Makita drill/driver, had a brushed motor and did all I asked of it and lasted around 20 years.
Even my less powerful Milwaukee makes a lot of noise and I won’t use it without hearing protection. The noise suggests that an impact driver is a brutal tool, but I was surprised by how much control it offered and impressed how well seated the driver bits stayed. My drill driver has cammed out of a lot of screws and ruined their slots in the process. The impact driver hasn’t done that yet, even when driving a 2″ brass #7 screw without a pilot hole. It won’t stop driving automatically because it doesn’t have a clutch, but I can watch the screw head come home and stop when it’s where it belongs. It’s going to be a very useful, often-used tool. Keeping up with the Lewises hasn’t disappointed me yet.
All of the impact drivers here are available from home-improvement centers and online retailers.
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