One common insert design has a wiping flat on the face of the insert. The width of this flat must be greater than the advance per revolution to allow the cutting edges to overlap. Spindle tilt is critical when using wipers. Due to the sharp ends on the insert, excessive spindle tilt can cause dig-in.
The MICRO MILL insert has four radiused cutting edges which project a very shallow ellipse in the plane of the cut. The large elliptical radius aligns to the surface regardless of spindle tilt. This ensures that the ends of the cutting edge do not dig-in the surface as can occur when inserts with conventional flats are used.
The cutting edge is ground with a hook as well as a radius so that the axial rake is positive. This creates a shearing action which eases entry into the cut and directs chips up and away so they do not cause scratches. With this type of insert, however, if the advance per revolution is too great, the elliptical cutting edges will not overlap enough to form a smooth surface finish.