| Field | Automotive maintenance |
| Went Obsolete | 1970s |
| Made Obsolete By | Increased use of disc brakes, environmental regulations |
| Knowledge Assumed | Moderate mechanical skills, knowledge of drum brakes |
| When useful | Optimizing performance of stock drum brake systems on older cars |
Drum brakes were standard on most cars through the mid-1960s. The purpose of arcing brake shoes is to optimize the fit of the shoe in the brake drum, maximizing stopping power by creating a larger, more uniform contact area. Drum shoes often arrived with loose tolerances and drums were notoriously out-of-round, even after turning on a brake lathe. An arcing machine is basically a grinder that removes material from the shoe to match it perfectly with the curve of the drum.
Unfortunately, the demand for this service has all but disappeared since disc brakes offer much improved braking power over drums. Also, since brake shoes are made of asbestos, grinding them is incredibly unsafe. Arcing machines still exist and are mostly owned by hobbyists.