The article presents the methods of study of geometric parameters of a working tool of a rail-milling train after revealing after the process of controlled operation of milling the polygon-shaped transverse profile of R65 rails not meeting the requirements of the standard. Those methods were tested in the case of rail-milling train of RFP-01 model. To eliminate the causes of formation of a poor-quality transverse profile, the specialists of JSC VNIKTI conducted a series of studies to establish the actual profile and incline of a working tool of milling wheels which are plateholders with carbide plates. A plate-holder from each milling wheel was randomly selected. The geometric parameters of plateholders were measured with a coordinate measuring machine. As a result of measurements, clouds of points of working surfaces of plate-holders were obtained. To compress and recognize images, a singular n × 3 matrix decomposition was used, where n is the number of rows equal to the number of points in the cloud, the columns are the coordinates X, Y, Z. The next step was to split the point cloud into triangles using the Delaunay triangulation algorithm. Using the above methods, plate-holders’ cutting lines were obtained that form the actually shaped rail profile. The cutting lines were aligned relative to the vertical axis with the R65 rail profile as per the condition of achieving the minimum root-mean-square deviation. As a result, the reasons for poorquality shape of R65 rail profile after milling were established, and recommendations were formulated for their elimination.