of springs for exerting a preload on the bearing some or all of the springs are at least partly made of a shape memory alloy so that the preload on the bearing can be adjusted with changes in temperature of the springs application_number US 57905990 A description referring to fig3 a machine tool includes a bed 1 a table 2 a column 3 a spindle head 4 and plural motors 5 6 7 11 a workpiece w is set on the table 2 the table 2 can move by means of the motor 5 in two opposite directions x perpendicular to the drawing the column 3 can move in two opposite directions y1 y2 by means of the motor 6 the spindle head 4 can move in two opposite directions z1 z2 by means of the motor 7 a tool holder 10 is detachably attached to a spindle 12 in the spindle head 4 a tool 13 held by the tool holder 10 rotates by means of the motor 11 referring to fig 1 the spindle 12 is rotatably supported by a frame 15 via upper ball bearings 16 17 and lower ball bearings 18 19 a tube shaped lower extension 20 has a flange 22 fixed to the frame 15 by means of bolts 23 a.