In metal additive manufacturing, achieving net-shape doesn’t always mean achieving net-tolerance. Critical surfaces, such as sealing faces, bearing seats, or assembly features, often require post-processing through CNC machining. But this step is only successful if the designer has accounted for it by adding machining stock.
Machining stock refers to the extra material (typically 0.2 to 0.5 mm) intentionally left on printed features to allow for finishing. Without this buffer, there’s no material to cut, meaning any surface that prints out-of-spec cannot be recovered. The result? Entire builds can be scrapped due to a few microns of dimensional error. This issue is especially common in assemblies requiring precision fits or leak-tight interfaces.
Designers should flag which surfaces are machining-critical early in the development process. These include faces that will be bolted, sealed, or aligned with mating parts. Working closely with manufacturing engineers ensures stock is added only where needed, minimizing unnecessary machining while protecting functional quality.
Another key is documentation. Call out “add machining stock” clearly on 2D drawings or model annotations, especially if your workflow passes through different teams. CNC operators rely on this info to set zero points and choose the right tools, don’t leave it to interpretation.
In summary, planning for machining is a small but critical step in ensuring the reliability and functionality of printed metal parts. It aligns AM with traditional tolerancing expectations and bridges the gap between design freedom and manufacturing reality.