Abstract: A machine tool for machining contains a tool attachment (9) to which a tool holder (7) for a lathe shaft (10) can be secured. The shaft (10) is mechanically secured in the tool holder (7), which means that vibrations occur when long shafts (10) are used. The invention reduces any vibration by arranging a tubular cavity (4) inside the wall surrounding the shaft (10) in the holder, and filling said cavity with a medium which is subjected to pressure so that the tool (10) is clamped with a force greater than that which can be achieved by mechanical means.