Last January I re-scraped the ways on a 1978 Kira-Seiki SL-3. The machine had drifted four tenths over its twenty-inch travel—barely enough to register, but enough to ruin every aerospace bore. The customer simply stopped calling.
The Myth of Repeatability
Modern CNC marketing sells repeatability as a solved problem. Hit cycle start, walk away, come back to perfect parts. But a test bar has no clamping forces, no thermal gradient, no chip accumulation. The gap between test bar and real part is where craftsmanship lives.
The tolerance block on a drawing is not an aspiration. It is a contract between the designer's intent and the machinist's capability.