A timber-working device includes a frame (8) having a feed axis (14) and a drive system configured to feed at least one stem along the feed axis (14). The drive system includes a first drive arm (9a) pivotally attached to the frame (8) on a first side of the feed axis (14), having a first rotary drive having a first wheel (11a). A second drive arm (9b) is also pivotally attached to the frame (8) on a second side of the feed axis (14), having a second rotary drive having a second wheel (11b). The drive system also includes a third rotary drive having a third wheel (12a), and a fourth rotary drive having a fourth wheel (12b), mounted on the frame (8) on the first and second sides of the feed axis (14) respectively. At least one processor controls operation of the rotary drives, such that in a first mode the speed of the respective wheels of the rotary drives on the same side of the feed axis (14) is substantially the same, and in a second mode the speed of the respective wheels of at least two rotary drives on opposing sides is substantially the same.
