This paper presents research on the accuracy and repeatability of CNC axis positioning in an innovative lathe with an additional Xs axis. This axis is used to perform movements synchronized with the angular position of the main drive, i.e. the spindle, and with the axial feed along the Z axis. This enables the one-pass turning of non-circular surfaces, rope and trapezoidal threads, as well as the surfaces of rotary tools such as a gear cutting hob, etc. The paper presents and discusses the interpretation of results and the calibration effects of positioning errors in the lathe’s numerical control system. Finally, it shows the geometric characteristics of the rope thread turned at various spindle speeds, including before and after-correction of the positioning error of the Xs axis.
After many years of intensive work the international experts from ISO TC 39 published the technical report called ISO TR 16907 “Machine tools – numerical compensation of geometric errors”. This document defines the terminology, presents benefits and limitations of numerical compensation of machine tools’ and measuring machines’ errors. It gives machines manufacturers and users vital information about how to use numerical compensation. In the context of those types of compensation defined in ISO TR 16907, this article shows rules of selecting models of Volumetric Error for three-axis machine tools. What is more, this paper presents some principles of reduction of these proposed models because of the functional tasks for machine tools. One of the obtained results is an array of reduced models for three-axis machine tools. This array determines the degree of detail of the model and the experimental research program that needs to be carried out in order to determine the Volumetric Error distribution.
In this paper circularity of three different machine tools by Virtual Machine was analyzed. To get circularity we make a ball bar test according to ISO 230-4. The test is very common in engineering for a quick diagnostic Computerized Numerical Control (CNC) technical conditions. We implemented earlier calculations of Volumetric Error in our Virtual Machine. Then we simulated testing of circularity of CNC machine tools. The place to take the test was chosen randomly from Uniform Distribution in three different kinds of machine tools. Those machines had different characteristics of kinematic errors and squareness and also different sizes of working space. We observed significant differences in the indicator (circularity) depending on the place where the test was taken. Moreover we showed that there was no reason to take the test in the center of working table.