The present disclosure includes a belt-and-pulley system for a part processing assembly. The part is retained on a spindle assembly of the belt-and-pulley system, and rotation of the spindle assembly is driven by a drive belt of the belt-and-pulley system that travels along a belt path. The belt-and-pulley system includes one or more idler assemblies that permit continuous rotation of the drive belt regardless of whether a part is being processed. As a part is processed, processing material, such as peening material, may be introduced near the belt-and-pulley system and may unintentionally interfere with operation of the belt-and-pulley system. The idler assembly of the belt-and-pulley system includes a vane sweep that is configured to block or prevent introduction of the processing material into the rotational operation of a circular pulley of the idler assembly. The vane sweep includes a top ledge that prevents introduction of peening material into a rotational aperture of the circular pulley and one or more fins that are configured to sweep or brush accumulated processing material away from the circular pulley. The vane sweep further includes an annular sheath that extends away from the circular pulley and surrounds a supporting member that supports or maintains the circular pulley, the annular sheath configured to further prevent processing material from interfering with rotational operation of the circular pulley. The location of the idler assemblies within the belt-and-pulley system may be determined to optimize the number of spindle assemblies that can be used to process parts simultaneously in the part processing assembly.