High precision machining in TMT (Thirty Meter Telescope) structure manufacturing

The Thirty Meter Telescope (TMT) is expected to reveal the birth of galaxies, planetary surfaces and even the atmospheric composition of exoplanets. The TMT is an optical infrared reflecting telescope that uses very large hydrostatic bearings in the drive units. High precision is required for the sliding surface of the hydrostatic bearing. In the case of TMT, the radius of the hydrostatic bearing of the elevation journal is about 10 meters and it cannot be manufactured as an integral structure, so has a segmented structure. The size of each member of the segmented structure exceeds 10 meters. When high precision machining of about 30 micrometers is performed on the large structure exceeding 10 meters, it may take several days for a single process, which is greatly affected by changes in ambient temperature. Changes in ambient temperature not only cause thermal expansion and contraction of the workpiece, but also cause deformation of the machine tool. There are only a few large machine tools that can process parts over 10 meters in size. We constructed a temperaturecontrolled chamber that covers the large machine tool to prevent ambient temperature fluctuations. We compared the accuracy of machining in a room temperature (variable temperature) environment and machining in a constant temperature environment. This result demonstrates that machining errors can be suppressed in a constant temperature environment. In addition, this paper also shows the results of combining machining and the use of abrasive paper to finish the sliding surface, which improved the surface roughness without deforming the shape of the machined sliding surface. By using these improved machining methods, we were able to establish a precision machining method for large structures.