Cordless impact drivers

Impact drivers are ideal for big assembly tasks

Cordless impact drivers are designed to provide more torque than regular drill/drivers. This lets them sink even large fasteners with minimal effort and without any strain on the hands and wrist. Often, impact drivers can sink fasteners without a pilot hole. When the tool senses resistance, an internal hammer gear initiates an impact motion, and torque increases dramatically -- with no extra effort required on the part of the user. Most impact drivers can also drill holes, but they're a lot slower at this than cordless drills. Most cordless impact drivers are best suited for big projects like building decks or installing cabinetry. However, for assembling furniture or putting up lots of shelves, reviewers recommend newer subcompact impact drivers in the 10.8-volt to 12-volt range.

A big advantage of impact drivers is that they tend to slip out of the screw or bolt head much less frequently than regular cordless drills. If you have a lot of assembling to do, or a big construction project with lots of fasteners, reviewers say an impact driver will make the job much more efficient and pleasant than a regular cordless drill/driver. The main drawback is the noise level, which definitely requires ear protection -- even for the subcompact drivers.

Most impact drivers use a quarter-inch hex chuck that takes both drilling and screw-driving bits with hex shanks. Bits slip in and out quickly, so if you do need a pilot hole you can switch bits instantly. If you prefer a regular chuck, attachments are available (*Est. $30). Cordless impact drivers are so efficient at their tasks that they don't need much voltage, so the only reason to buy an 18-volt impact driver is to save money by using the same batteries and charger your cordless drill uses.

Subcompact impact drivers

If you plan to drive a lot of small fasteners, consider the 12-volt Bosch PS40-2A (*Est. $150), which earns enthusiastic praise at Fine Woodworking. Unlike most impact drivers, it can't drill holes -- it just drives screws. Pilot holes generally aren't needed, however, and the Bosch only weighs 2.2 pounds. A built-in LED light rings the chuck to illuminate the work area. This little impact driver gets high praise in owner-written reviews at retailer site NorthernTool.com, and tests at Toologics.com find the Bosch PS40-2A as powerful as a Bosch hammer drill that weighs three times as much. As for drawbacks, reviewers say the Bosch PS40-2A is loud and lacks the power needed for really big fasteners.

The Bosch PS10-2A I-Driver (*Est. $150) can maneuver into even tighter spaces because of its 90-degree pivoting head, so you can make the tool nearly vertical. The I-Driver is also versatile, drilling up to a maximum speed of 600 rpm. This is a lot slower than a two-speed drill/driver such as the Makita DF030DW (*Est. $150), but faster than the Bosch PS20-2A Pocket Driver (*Est. $100). Editors at Fine Woodworking and Popular Mechanics note, however, that at 2.5 pounds, the I-Driver is pretty heavy. Bosch's Li-ion batteries also don't perform particularly well in cold weather.

Newer competitors get better marks for cold-weather performance, and rank high for overall comfort and performance as well. They also carry longer warranties -- 10 years for the Hitachi, three for the Makita -- compared with one year for the Bosch tools. The 10.8-volt Makita TD090DW (*Est. $120) is the top pick in recent comparison tests at Woodworker's Journal. Popular Woodworking also recommends it in a December 2008 piece. The Makita weighs just 2 pounds and comes with a holster; the handful of owners rating it at Amazon.com gives it enthusiastic reviews.

Larger cordless impact drivers

Comparison tests of Li-ion impact drivers at Fine Homebuilding conclude that weight is a decisive factor. Impact drivers that weigh less than 3 pounds vibrate too much, while the drivers that weigh more than 3.5 pounds are tiring to use. Based on several months of testing, editors rank the 3.2-pound 14.4-volt Panasonic EY7540LN2L (*Est. $315) at the top, saying it hits the "sweet spot" for impact-driver weight.

The Li-ion-powered Panasonic impact driver also includes a work light and earns praise for its variable-speed trigger and flawless performance across a wide range of fastening tasks. The Panasonic EY7540LN2L also earns the top spot at Tools of the Trade, whose tests show it outperforming several 18-volt Li-ion tools. It has a brushless motor and the tool automatically protects itself from overheating. The main drawback is that the direction switch is easy to change by accident. It's also expensive compared to 18-volt cordless drills.

Makita also makes well-recommended Li-ion impact drivers that fall in ideal weight range, and they carry three-year warranties. Reviewers like Makita's efficient four-pole motors, handy belt hook and the way the LED lights stay on several seconds after the trigger is released so you can check your work. Three reviews recommend the 3.3-pound, 18-volt Makita BTD141 LXT impact driver kit (*Est. $255), which also has 3.0-Ah Li-ion batteries.

If low price matters more than weight, vibration, power and runtime, the Ryobi P230 impact driver (*Est. $70 w/o battery) performs reasonably well in tests. Its Ni-Cd battery and charger are sold separately (*Est. $60) and can also be used with other Ryobi ONE+ cordless tools. The Ryobi P230 is also compatible with the newer Ryobi Li-ion batteries (*Est. $100). We found the most detailed review of the Ryobi impact driver at ContractorTalk.com, where tests show it can drive a 3/8 lag screw 1.5 inches long, but not one three inches long. Pronounced vibration is also an issue, and if you plan to use an impact driver a lot, critics recommend spending more for a better model.