Guides / Process

5-Axis Machining Accuracy: Calibration and Rotary Axis Error

September 26, 2026

A 5-axis machine can hold tighter tolerance across more of a part in one setup than a 3-axis machine ever could, but only if the two rotary axes are calibrated as carefully as the three linear ones. A machine with drift in its rotary axes can produce a part that measures fine at the center of rotation and drifts out of tolerance toward the edges.

Where the error actually comes from

Every axis on a machine has some positioning error, but a rotary axis multiplies that error by distance from its center. A small angular error in the rotary table becomes a larger linear error the further a feature sits from the pivot point. This is different from 3-axis error, which stays roughly constant across the work envelope, and it is why 5-axis accuracy cannot be assumed from linear axis specs alone.

Kinematic calibration

Most modern 5-axis controls support kinematic calibration, a process that measures the actual geometric relationship between the rotary axes and the linear ones, then compensates for it in software. This corrects for the machine not being built exactly to nominal geometry, which no machine is. Without this calibration, a 5-axis machine can produce parts that check out near the table center and drift as features move away from it.

How shops verify it

A ballbar test measures a machine’s circular motion against a known reference and reveals errors that would otherwise only show up in a finished part. Some shops run this on a schedule, others run it after any event likely to affect accuracy: a crash, a major repair, or moving the machine. In-process probing on a part, discussed in a separate guide on inspection, catches problems at the part level but does not replace machine-level calibration.

What this means for tolerance

A well-calibrated 5-axis machine can hold ±0.02 to ±0.05 mm across most of a complex part, depending on size and material. A machine overdue for calibration may hold that near the table center and lose it toward the edges of larger parts, which is a common and hard-to-diagnose source of failed inspection on large 5-axis work. Part size and where features sit relative to the rotary center both affect what is realistic.

What to ask a shop

Ask when the specific machine that will run your part was last calibrated, not just when the shop’s equipment generally gets serviced. Ask whether a ballbar test record is available. For a large part with features spread across the table, ask specifically how the shop accounts for rotary axis error across that distance, since this is exactly where an uncalibrated machine struggles most.

The short version

Adding rotary axes adds a real source of error that a shop has to actively manage, not something a 5-axis machine handles automatically. Calibration and verification testing are what make the tight tolerance claims on a quote actually true. A shop that tracks this openly is a good sign; one that cannot answer the question is worth a closer look.

This post is part of our guide to 5 axis machining quality control.

See also: typical 5-axis tolerances by feature.

Frequently asked questions

Keep reading

• Thermal Growth on 5-Axis Machines and How Shops Control It
• Collision Checking and Machine Simulation Before a 5-Axis Run