**5. Cutting mechanism and material deformation in diamond turning**

The cutting edge radius of the diamond tool in ultraprecision machining affects the cutting mechanisms. The uncut chip thickness (a) is of usually comparable size as the tool edge radius (r) in diamond turning and their ratio governs the cutting mechanism viz. shear plane cutting, plowing and sliding. These mechanisms in turn decides the resulting surface quality. There exists a 'minimum uncut chip thickness' below which no material removal takes place due to cutting. The minimum uncut chip thickness depends on the tool geometry which includes edge radius, rake & flank plane angle and the workpiece material properties. Sliding at the flank face due to elastic recovery of the workpiece material and plowing due to edge radius of the tool becomes dominant in ultraprecision machining.
