This paper introduces a method for in-process tool wear estimation of an air turbine spindle, which is equipped with a rotation control system for ultra-precision milling. Previous investigations revealed that the pressure of the compressed air for supply that is used to control the rotational speed and tool wear at the time when steady wear occurs, maintains a linear relationship when processing SKD61 steel. In addition, the extent to which the supply pressure changed was reduced after chipping occurred. Therefore, the possibility exists that the tool wear can be estimated by obtaining the supply pressure during processing. The purpose of this paper is to propose the evaluation of an in-process tool wear estimation method, and to evaluate its validity. An estimation method is necessary as this would allow the amount of tool wear to be estimated and abnormal wear of occurrence to be detected. Because of the linear relationship between the air pressure and the amount of tool wear, the latter can be estimated by plotting the approximately linear relationship of the tool wear as a function of the air pressure. The proposed estimation method for processing the results obtained for SKD61, is capable of estimating the relative error of the measured value within 0.2 against the estimated value at the time. Furthermore, the occurrence of abnormal wear is determined from the amount of change in the supply pressure. Thus, SKD11 steel was processed for the proposed estimation method to verify whether it is valid for cutting high hardness steel. As a result, for SKD11 the estimation method produced estimation results similar to those obtained for SKD61. Therefore, the suggested estimation method is likely to be effective for high-hardness steel cutting.

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On-machine measurement is used in ultra-processing machining, but it is seldom used in precision machining. For on-machine measurement, it is necessary that the sensor not be easily affected by the moving error or environment vibration in the field of precision machining. A triangulation method sensor with the optical skid method made using a new design concept is proposed to remove the moving error and vibration. The optical skid method used two laser spots with different sizes: the small spot diameter is the stylus and the large spot diameter is the skid [1]. The difference between these two signals reflects the surface shape. The developed sensor comprises an optical source and two optical receiving systems. Each optical receiving system has an imaging lens and a detector. Instead of two laser spots of different sizes, two detectors with different sizes of receiving area serve as the optical skid. Results confirmed the possibility of reducing the influence of the vibration using the developed sensor. In on-machine measurements, measurement of the surface profile with long wavelength is often necessary. If the spot diameter of the skid is not much larger than the surface profile wavelength, then the smoothing effect of the skid is reduced. Therefore, the amplitude of the measured profile by the skid sensor is smaller than actual amplitude of the workpiece. This paper presents a method of reconstructing the surface profile from the measurement results and the obtained effects of the reconstruction method from simulations and experiments.