Metrological apparatus

There is described a metrological instrument including a turntable 5 for supporting a workpiece and a support for supporting a stylus gauge (17, fig. 10). The support includes a support body (11, fig.1) and an attitude arm 13 which is mounted to the support body so as to be rotatable about a pivot axis 15. The attitude arm 13 holds the stylus gauge (17) which generates a signal representative of the deflection of the stylus in a measurement direction as the stylus follows a surface of the workpiece on rotation of the turntable about the spindle axis 31. An attitude switching mechanism allows rotation of the attitude arm 13 about the pivot axis 15 to switch the attitude of the stylus between a first attitude in which the stylus is generally aligned with the spindle axis 31 and a second attitude in which the stylus is generally aligned perpendicular with the spindle axis. The attitude arm includes a first adjuster 33a for moving the stylus tip in a direction perpendicular to both the spindle axis and the measurement direction when the stylus is in the first attitude to allow alignment of the measurement direction with the spindle axis, and a second adjuster 33b, for moving the stylus tip in a direction perpendicular to both the spindle axis and the measurement direction when the stylus is in the second attitude to allow alignment of the measurement direction and the spindle axis. An orientation mechanism (inc. motor 73, fig. 10) is provided which rotates the measurement direction of the stylus. A stylus tilt mechanism (eg. 91, 97, fig. 13) allows the stylus to be tilted about a tilt axis which is parallel with the measurement direction.