Abstract : This paper studies the detection method of roll angle error of vertical axis of CNC machine tool based on the straightness error measurement of laser interferometer. The relationship between the measured value and the original error is analyzed using homogeneous coordinate transformation, and a roll angle error detection model is established on this basis. The principle of laser interferometry measurement of straightness error is analyzed, and an electronic level is used as the reference benchmark for relative orientation. A vertical roll angle measurement method and device based on dual straightness detection is presented. Roll error detection experiments on the horizontal axis are conducted according to the detection principle of this method, and the results are compared with those obtained by direct measurement with an electronic level. No significant difference is found between the two results. This method and device are also applicable to the detection of roll angle error of inclined linear axes in the vertical plane. Keywords : Roll angle error; CNC machine tool; Vertical axis; Electronic level; Interferometry 0 Introduction The development direction of mechanical manufacturing equipment is high precision, high flexibility, and automation. Accurate measurement of geometric errors is the foundation for error compensation and thus improving the accuracy of CNC machine tools. Any linear motion axis of a machine tool has pitch, yaw, and roll angular motion errors. The existence of these original errors will cause changes in the relative posture of the tool and the workpiece, thus forming machining errors in the workpiece. Compared to the detection of the first two types of errors, the detection of roll angle error, especially the roll angle error of the vertical axis, has always lacked effective, simple, and high-precision measurement methods. Laser interferometers, as a high-precision detection method, have been included in relevant machine tool testing standards and can perform high-precision detection of pitch and yaw angle errors, but cannot directly measure roll angle error. For the roll angle error of the horizontal axis, a level is usually used for measurement; for the roll angle error of the vertical axis, indicators such as dial indicators are usually used with the aid of physical references such as straightedges and cylindrical squares. These traditional detection methods have disadvantages such as low efficiency and limited accuracy, and are inconvenient for detecting the roll angle error of the tilt axis. Therefore, research and exploration of methods for detecting roll angle error are still ongoing both domestically and internationally. Besides traditional methods, the methods proposed by scholars can be mainly classified into two categories: methods with reference references, such as measurements based on the collimated laser position, measurements based on the collimated laser direction, and measurements based on the collimated laser polarization direction; and comprehensive identification methods without reference references. The former often requires specialized testing equipment, while the latter is based on the prior measurement or identification of other original geometric errors. Since laser interferometers are the main high-precision testing equipment for machine tool error detection and accuracy evaluation, and have wide applications in production and scientific research, exploring roll angle error measurement methods based on laser interferometers is of great significance. This paper takes this as its starting point and studies a method for measuring vertical axis roll angle based on straightness error measurement. [Full text download of a new method for measuring vertical axis roll angle error]