Abstract: A blade assembly normally driven by a power takeoff shaft has a frame normally displaced in a travel direction and provided with a pair of blade carriers horizontally reciprocal transverse to the direction. The drive unit comprises a right-angle transmission having a horizontal input connected to the power takeoff shaft and a vertical output, a vertical shaft offset from the output and having a pair of angularly offset eccentrics, and a belt drive interconnecting the transmission output and the vertical shaft. A pair of relatively long actuating arms extending in the direction flank the transmission and shaft and have rear ends pivoted on the frame and front ends connected to the respective blade carriers. A pair of respective connector plates extending transversely of the direction have respective inner ends carried on the eccentrics and outer ends connected to the arms between the ends thereof.