Ac

AC stands for across corners, the distance measured from one external corner to the opposite corner of a hex, square, or other non-round feature on a CNC drawing. It defines the maximum diagonal envelope that controls fit through bores, slots, fixtures, or mating components. In electrical CNC documentation, AC can also mean alternating current for servo drives and spindles.

On the shop floor, AC governs the overall envelope of a feature that must fit into a bore, slot, fixture, or mating component because the corners usually create interference first. For a hex machined on a live-tool lathe, the operator checks the corner-to-corner size with calipers or a comparator when the print specifies AC, even if a secondary across-flats dimension is also controlled. The same logic applies in millwork and edgebanding on square plugs, decorative inserts, and framed parts where fit depends on the longest diagonal rather than the nominal face size. Meanwhile, in electrical documentation, AC refers to alternating current; AC servo motors and spindle drives use it for precise motion control. Reading the context correctly prevents setup and inspection errors, especially when both geometry and electrical terms appear on the same machine sheet.

• ⚠️Confusing AC with AF: Reading a hex print as across flats instead of across corners produces a part that calipers show as correct but that cannot enter its mating pocket because the corner envelope exceeds the available clearance.
• ⚠️Wrong inspection method: Checking only face-to-face size on a corner-controlled profile misses corner stock, cutter radius error, or burrs, so the part passes inspection yet jams at assembly.
• ⚠️Electrical meaning mix-up: On machine sheets AC may refer to alternating current, and treating it as a geometry callout can mislead setup notes around servo drives, spindle power, or control cabinet documentation.