9.10 Wheel Dressing Procedure—The preferred dressing procedure for the periphery of the rubber rim is to mount a diamond-cut file9 in place of the specimen in the holder and run the machine with load until the wheel is clean. Another dressing procedure for the periphery of the rubber rim is to mount the wheel on a lathe, and machine the surface with a tool bit especially ground for rubber applications. Grind a carbide or high-speed steel tool bit to very deep rake angles (Fig. 12). Feed the tool across the rubber surface in the opposite direction from that normally used for machining steel. This allows the angular surface of the tool bit to shear away thin layers of rubber without tearing or forming grooves in the rubber as would occur when using the pointed edges of the tool. The recommended machining parameters are: Feed—25 mm/min (1.0 in./min); Speed—200 rpm; Depth of Cut—0.254 mm (0.010 in.) to 0.762 mm (0.030 in.). The dressed wheel should be first used on a soft carbon steel test specimen (AISI 1020 or equivalent) using Procedure A. This results in a smooth, uniform, non-sticky surface. An alternative dressing method involves the use of a high-speed grinder on the tool post of a lathe. Take great care since grinding often tends to overheat and smear the rubber, leaving a sticky surface. Such a surface will pick up and hold sand particles during testing. If the grinding method is used, not more than 0.05 mm (0.002 in.) may be ground from the surface at one time so as to prevent overheating.