Pendulum saw

A pendulum saw or swing saw is a mechanically powered circular saw with the blade mounted so it can swing into the material.
Operation.
A swing saw is used for cross cutting wood in a sawmill, or for cutting ice off of a frozen body of waters. The saw is hung on a swinging arm, sometimes with a counterbalance weight. 
A swing saw is also sometimes called a "cut-off trim saw" in a mill for cutting right angle to the direction of the wood grain. A swing saw is a very dangerous tool, even with a blade guard. Early models were driven by a belt, usually made of leather, that was powered by a water mill or later a steam engine. Today the power source is an electric motor or a gas engine
Harbin International Ice and Snow Sculpture Festival.
Swing saws are used to carve ice blocks from the frozen Songhua River for the Harbin International Ice and Snow Sculpture Festival each year.