As the name suggests this cutter is designed for undercutting mushroom shapes, but is also ideal for hollowing out small forms. Sharpening: Use a diamond file or honing stone across the top face. To gain best results and increase the longevity of the cutter this simple procedure should be done little and often. Use the TurnMaster cutter holder to reshape the profile on the Robert Sorby ProEdge using a zirconium or ceramic belt or on a grinding wheel using a standard abrasive material. Sharpens to: 0.2-0.4 microns Hardness: 62 RC Material: M2 HSS. Related Products: These cutters are designed specifically for the TurnMaster.