Abstract <p>The article describes the results of tool wear tests of a tool for deformational cutting in external finning of copper heat-exchange tubes. The test method and equipment are presented. The tool wear topography is analyzed, the tool wear criterion is determined, and graphs of changes in linear and mass wear parameters are constructed. The tool wear life was 90 min at a cutting path of 13.3 km. A three-tool copper tube finning machine with the given tool life provides finning of 368 linear meters of tubes.</p>