ISO/TR 16907:2015

Overview

ISO/TR 16907:2015 - Machine tools: Numerical compensation of geometric errors is a Technical Report that explains how numerically controlled (CNC) machine tools can use numerical compensation to reduce geometric errors. The report covers terminology, representation of error functions from different measuring methods, classification of compensation methods used by CNCs, and guidance for applying various numerical compensations. It focuses on geometric errors under no‑load or quasi‑static conditions and explicitly excludes dynamic-force‑induced errors and other part‑quality influences (e.g., tool wear). Measurement procedures themselves are not detailed here - those are covered by ISO 230 (all parts).

Key topics

• Terminology and definitions: machine tool coordinate system, functional point, functional orientation, motion compensated/uncompensated for geometric errors.
• Kinematic and error representation: kinematic representation of machine structure and representation of error functions, including look‑up tables and spatial error grids.
• Classification of compensation methods: detailed types such as L‑POS, L‑STR, L‑ANG, L‑VOL, L‑VOL+ for linear axes and R‑POS, R‑RAX, R‑VOL, R‑VOL+ for rotary axes, plus machine‑specific (L‑SPEC, R‑SPEC).
• Determination of geometric errors: considerations for direct and indirect measurement, selection of coordinate systems, superposition of individual errors, and treatment of non‑rigid behaviour.
• Practical factors affecting compensation: role of temperature, repeatability, least increment step of the machine, and effects of workpiece/tool mass (with deformations due to changing static load addressed).
• Implementation and validation: how to generate compensation tables/grids, alignment of compensated motion, validation, measurement uncertainty, traceability and documentation requirements.

Applications and users

ISO/TR 16907:2015 is intended for practical use by:

• Machine tool manufacturers and suppliers - to design and integrate numerical compensation strategies that improve volumetric accuracy.
• CNC integrators and control vendors - to classify and implement compensation types and error tables in controllers.
• Metrology service providers and instrument manufacturers - to represent measurement outputs for compensation inputs (look‑up tables, spatial error grids).
• Production and quality engineers - to evaluate when numerical compensation can reduce part‑making cost, maintenance, or mechanical re‑fitting.

Practical applications include improving part accuracy via volumetric compensation, creating spatial error grids for complex multi‑axis machines, and documenting compensation for traceability and validation.

Related standards

• ISO 230 (all parts) - test codes for machine tool geometric accuracy and measurement techniques.
• ISO 230‑1:2012 - geometric accuracy of machines operating under no‑load or quasi‑static conditions.
• ISO 841:2001 - numerical control coordinate system and motion nomenclature.

Keywords: ISO/TR 16907:2015, numerical compensation, geometric errors, machine tools, CNC, volumetric compensation, spatial error grid, error tables.