Bit Holders, Depth Stop, & Clutch
Bit Holder. A free-spinning collar on the bit holder's nose helps protect the bit holder itself from impact, like when the tool thrusts into a cavity in block, but more importantly it protects the end seal. Not only does the end seal keep abrasive dust out of the bit holder, it helps keep the grease inside from escaping. And since an expensive bit holder is the most common replacement on these tools besides brushes, that detail is important to me. Metabo's metal collar is the toughest. All the bit holders free spin, except Hilti's. Hilti acknowledges the importance of a good end seal, however, and is the only company to mention it in the manual, offering theirs as a replacement part for less than $10.
The Metabo has a lot of ambitious features like chipping and multiple speeds. It's also the only tool to ship with a keyless chuck accessory for wood-boring bits.
Credit: Photo: David Sharpe
Depth Stops. The Bosch, DeWalt, and Milwaukee depth stops have positive locking notches that stop the drill solidly every time. And their easy lever adjustment was quick and didn't require loosening the front handle like the Hilti, Hitachi, Makita, and Metabo. I could defeat these four friction-held stops by pushing moderately hard or bottoming out hard a few times. If you crank them down tight and then watch it as you bottom out, they work fine.
Clutch. It's an unwritten law that rotary hammers have a clutch, and for good reason–when bits stop in concrete it's sudden and it's solid. A good clutch also provides peace of mind, because it means I don't have to maintain a death grip on the tool to keep it from injuring me if the bit snags on a piece of rebar.
The Hitachi (top) and Makita have different, but easy-to-engage, selector switches.
Credit: Photo: David Sharpe
I tested the clutches by impacting a spinning bit against rebar inside a hole then did a physical evaluation of reaction torque (again, no test lab equipment in sight). In other words, I felt how hard they twisted against my grip. The Makita, Bosch, and Hitachi had low reaction forces, while the Hilti and DeWalt had higher, yet manageable, forces. The Milwaukee's motor slowed and strained, almost stalling before the clutch activated with high force.
Metabo's clutch action is electronic and reduces power to the motor when a bit jams. At first, I thought there was no clutch action because instead of the mechanical clutch clatter that is audible on the other tools, the motor slowed and made straining noises as the bit jammed. The tool put up a fight, requiring a high reaction torque to engage the electronic clutch. When I hit rebar on the jobsite, the Metabo was the only one in the group that spun out of my grasp. It gave me a good whack while wrapping its cord around itself and bending a 1/2-inch bit.