5-Axis Tolerance Guide
What tolerances to expect from 5-axis machining in production — not machine brochure specs, but what shops hold on real parts.
Simultaneous 5-Axis Tolerances
Simultaneous 5-axis machining achieves ±0.001" to ±0.0005" on contoured surfaces in production. The tolerance is driven by machine dynamic accuracy — as axes move simultaneously, interpolation errors, servo lag, and mechanical backlash all contribute to deviation.
On high-end machines (DMG Mori, Hermle, Mazak Variaxis tier), simultaneous contouring accuracy is typically ±0.0003"–0.0005". On mid-range machines, expect ±0.0005"–0.001". CAM programming quality matters as much as the machine.
3+2 Positional Tolerances
3+2 machining locks the rotary axes and cuts in 3-axis mode from an indexed angle. This eliminates interpolation error. Tolerances of ±0.0005" to ±0.0002" are achievable because only three linear axes move during cutting.
The critical spec is rotary axis indexing repeatability — typically ±0.001° or better on quality machines, translating to positional accuracy well within ±0.0002" at typical part dimensions.
Factors That Affect Accuracy
Thermal stability
5-axis machines are sensitive to thermal growth in the spindle, rotary axes, and ballscrews. Shops holding tight tolerances run climate-controlled environments or use thermal compensation in the control.
Fixture rigidity
When parts are indexed to steep angles, cutting forces create moment loads that don't exist in conventional 3-axis work. Fixtures designed for multi-angle access — tombstones, hydraulic vises, custom 5-axis fixtures — are essential.
Tool length
5-axis work often requires longer tools for clearance at compound angles. A 6" endmill deflects ~8x more than a 3" endmill of the same diameter. This is the primary source of error on deep-reach features.
If your drawing has a tight tolerance on a feature requiring a long tool at a compound angle, talk to your shop. A fixture redesign or sequence change that allows a shorter, more rigid tool can save the tolerance — and save you money.
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