Precision turned metal parts: what “precision” actually means

Every machine shop calls itself precise. The word only becomes useful when you ask three questions: how tight, measured how, and proven over how many parts.

“Precision” on a supplier's website means nothing on its own. What means something is the answer to three questions, and any shop that machines industrial metal components to drawing should be able to answer all three without hesitating.

1. How tight, and on which feature?

A drawing usually has one or two characteristics that decide whether the part works, and a dozen that do not. Tightening everything to the same tolerance does not make a better part — it makes an expensive one. What matters is that the functional features are held, batch after batch.

2. Measured how?

A measurement is only as good as the instrument and the person. The rule of thumb is that the measuring system should consume no more than about a tenth of the tolerance it is checking; beyond that you are measuring your own gauge. That is why a tolerance of a few microns is not a caliper job. We measure on coordinate measuring machines, with optical systems and with component-specific gauges, and we run gauge studies on the systems themselves.

3. Proven over how many parts?

This is the question that separates a workshop from a series supplier. One good first article proves nothing. Capability studies — Cm and Cmk on the machine, Cp and Cpk on the process — say how much of the tolerance the process actually uses and how much margin is left before something drifts out. On critical characteristics we also sort 100% by camera rather than trust a sample.

What we hold

Micron tolerances on turned diameters, on sliding head automatics built for it, in metal components from Ø 2 to Ø 52 mm. The achievable tolerance depends on the material, the geometry and the process, so we say what is realistic on a specific drawing rather than publishing a number that flatters us.

More on how we measure and document, or send a drawing to info@kovinski-izdelki.si.