Engineering Resource
Anyone can write ±0.005 mm on a drawing. Making it repeatably true across a batch is a process question, and this guide covers what that process needs.
What a tight tolerance requires
- A machine rigid and accurate enough to cut the feature without deflection.
- Sharp tooling at the right geometry, replaced before wear reaches the tolerance.
- Fixturing that holds the part without deforming it.
- Thermal control, because the part and the machine both move with temperature.
- Measurement capable of resolving a fraction of the tolerance.
Temperature is the quiet variable
Steel expands roughly 12 µm per metre per °C; aluminium about twice that; plastics far more. A part cut warm and measured warm can read perfectly and be out of tolerance at rest. Tight work is therefore machined with heat controlled and measured in a stable environment — and stress-sensitive parts are measured only after they have relaxed.
Process capability, not luck
A tolerance is only held if the process produces conforming parts repeatedly, not if one part happens to pass. That is why tight work uses stable parameters, predictable tool life and a measurement loop that feeds back into the process rather than sitting at the end of it.
Where the limit is
We hold ±0.005 mm on 3-axis work and ±0.01 mm as standard on simultaneous 5-axis, verified on a Zeiss CMM for geometry and position, the TRIMOS V5 height gauge for heights and steps, and the AI-Vision system for fine features. Tighter than that stops being a machining question and becomes a metrology and cost question — worth discussing before the drawing is frozen, not after.