Refinishing

If you determine a drum needs refinishing, remove only enough metal to obtain a true, smooth braking surface. If a drum does not clean up when refinished to the maximum refinish diameter replace it. Removal of more metal will affect heat dissipation and can cause drum distortion. All brake drums have a maximum diameter cast into them. This diameter is the maximum wear diameter and not a refinish diameter. Do not refresh a brake drum that will not meet the Specifications replace it. When you refinish a brake drum, resurface the drum to a dimension not more than 0.76 mm (0.030 inch) less than the discard diameter. The refinish diameter is the maximum diameter the drum can be refinished to and still allow safe braking action. If you exceed this diameter, the brake drum will wear beyond the discard diameter during normal brake use. Always use sharp cutting tools or bits. Dull or worn tools leave a poor surface finish that will affect initial braking performance. Always use vibration dampening attachments when you refinish braking surfaces. These attachments eliminate tool chatter so you can obtain a better surface finish. The best speed for refinishing braking surfaces is a spindle speed of 150 RPM. Crossfeed for rough cutting should range from 0.15 to 0.25 mm (0.006 to 0.010 inch) per revolution. Finish cuts should be made at crossfeeds no greater than 0.05 mm (0.002 inch) per revolution.