An investigation has been completed to determine the feasibility of using vibration measurement to develop an online tool wear monitoring system.Conventionaltransducers and FFT signal analysers have been used as the starting point for data collection and analysis. Additional software has been developed in order to obtain additional and enhanced analysis using statistical data such as percentile analysis and 4th statistical moments. The signal analysers have been interfaced with an IBM compatible PC to allow efficient data collection and analysis. • The measurement of surface finish via the use of centre line average has been selected as the primary indicator of tool wear. An experimental programme has been completed which examines the relationship between vibration measurement and surface finish during turning operations. This has provided sufficient general rules and guidelines to enable the method to be extended to other processes. It also provides information from which commonly occurring faults such as looseness of the tool holder, changes in material properties and swarf presence in the toolholder can be identified. Tests have been completed using cast iron, ENS and EN3 steels. An expert system has been developed. It has been demonstrated that sufficient data can be collected during the setting-up stage or commissioning part of a machining process from which, using the expert system, reliable tool wear monitoring can be achieved for all subsequent tests. In addition to predicting'the surface for all stages of tool life, the system can identify common faults such as looseness of the toolholder, the presence of swarf in the toolholder and changes in material properties. This system has been evaluated in relation to the available data, the present expectation of quality assesment required from the machine operation and relative to available commercial monitors. The system offers significant improvements.