To make the Hackzall’s compact and comfortable profile, engineers put a dogleg between the handle and the blade to hold the motor (most recips place the motor in-line). A lightweight gearset carries the motor’s spinning motion around the bend to the blade, which traces the same oval-shaped cutting motion as a full-size recip. Although the Hackzall can use standard reciprocating-saw blades, Milwaukee sells special four-inch blades, which are thinner and make a finer cut. That helps reduce strain on the motor, so a single charge gives you plenty of wanton destruction.
