Pencil milling

Pencil milling is a cleanup toolpath generated by computer-aided manufacturing (CAM) programs to machine internal corners and fillets with smaller radius tools to remove the remaining material that are inaccessible with larger tools used for previous roughing, semi-finishing, and finishing toolpaths. The name comes from the way that a pencil could naturally be drawn along these corners. It is sometimes called a rolling ball toolpath.

Often a constant step-over passes are derived from single pencil pass to create parallel pencil passes that are very good for cleaning up corners and fillets where excess material remains from a bigger cutter.