A cutting deck of first and second cutting blade inner rotation of a cutting chamber is provided for accommodating. Cutting deck includes a weldment of a top plate and side plate. Top plate includes first and second axis receiver hole, and limits between flow control assembly and side plate a flow control assembly of the slave top plate extension of an airflow channel. Flow control assembly includes the close first axle receiver hole of second axis receiver hole and the first change in orientation part of second change in orientation part. First and second change in orientation part is separated from each other by straight portions. First and second change in orientation part passes through straight portions only by those of respective first and second cutting blade, two first and second cutting blades.
