Machine Tool Metrology

Summary:

Machine tool metrology is a process of ensuring that machine tools in a workshop produce workpieces with consistent accuracy within prescribed limits. This depends on the stiffness and rigidity of the machine, alignment of machine parts, and accuracy of control devices and driving mechanisms. Machine tools are tested at various stages to determine if they meet specifications, including alignment tests and performance tests. Performance tests involve preparing actual test jobs on the machine to check the accuracy of produced parts. Working accuracy also depends on factors such as cutting tool geometry, the material of the workpiece, cutting speed, work holding, and operator skill. Various geometrical checks are made on machine tools to ensure straightness, flatness, parallelism, and perpendicularity. The quality of the guiding and bearing surface of machine parts is also tested. Instruments used include dial gauges, tests mandrills, straight edges, squares, spirit levels, and autocollimators.

Excerpt:

Machine Tool Metrology

Machine tools for the workshop must be able to produce work-piece of given accuracy within prescribed limits consistently and without require in artistic skill on the part of the operator and the quality of workpieces depend upon:
1. Stiffness and rigidity of the machine tool and its components parts.
2. The alignment of various machine parts in relation to one another.
3. The quality and accuracy of the control devices and the driving mechanism.

Machine tools are tested at various stages, during assembly, after assembly, installation, repairs, or overhauls as per the accuracy test chart in order to determine whether it meets requirement of specification or not.

Acceptance test for a machine tool
1. Alignment test or Geometrical test
2. Performance test or Practical test

An alignment test is carried out to check the grade of the manufacturing accuracy of the machine tool.

It consists of checking the relationship between various machine elements (such as bed, table, spindle, etc) when the machine tool is idle and unloaded.