| 摘要 |
A hammer drill includes a body, a motor; a centre of gravity, and a hammer mechanism driven by the motor in reciprocating movement along a hammer axis at a first distance from the centre of gravity. A counter mass is mounted within the body for sliding movement along a slide axis at a second further distance from the centre of gravity. A biasing member biases the counter mass to a mid-position along the slide axis. The biasing means may be a leaf spring or a helical spring. The counter mass may be slideably supported on rods and may be able to twist about a number of axes.
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