Shave shallow layers of material off your workpiece to create a smooth even finish. These fly cutters hold a lathe tool (sold separately) and run on your milling machine. Compared to end mills, these make a wider cut per pass. They also generate less heat, so you can run them at higher speeds. In the long run, these cutters will save you the cost of replacing entire end mills once they dull—you can either sharpen your worn lathe tool or just replace that one part.