Alignment tests on a lathe

Alignment (geometrical) tests check the accuracy of the machine tool itself, without cutting: that the slideways are straight, the spindle runs true and the moving parts are parallel or square to each other. The results are compared with the permissible values given in standards (for example the ISO 230 series). The quality of the workpieces depends on the accuracy of the machine.

Test for level of installation

The machine is installed on a firm foundation. A precision spirit level (0.02 mm/m) is placed on the bed, at the headstock end and then at the tailstock end, along the bed and then across it, with the carriage at various positions. The readings are noted and the levelling screws or wedges are adjusted until the bed is level in both directions to within 0.02 mm per 1000 mm. This ensures that the bed is not twisted or sagging under its own weight and that the other tests are valid.

Spindle tests

1. True running (runout) of the spindle nose: a dial indicator is held on the carriage with its stylus on the nose of the spindle (or on the locating cone), and the spindle is rotated by hand; the movement of the pointer is the runout (typical permissible value about 0.01 mm).
2. Runout of the spindle taper (axis): a test mandrel is fitted in the taper bore, and dial indicator readings are taken near the nose and at 300 mm from it. The readings give the eccentricity and the alignment of the axis (permissible 0.01 mm near the nose and 0.02 mm at 300 mm).
3. Axial slip (end float) of the spindle: a dial gauge touches the centre of the spindle end face (or a steel ball in the centre hole) while the spindle is rotated and pushed along its axis; the pointer movement is the axial slip (about 0.01 mm).
4. Parallelism of the spindle axis with the bed: the dial indicator is traversed with the carriage along the test mandrel in the vertical and horizontal planes. The readings should be within 0.02 mm over 300 mm, and in the vertical plane the free end of the mandrel may only be higher, not lower.