Need of alignment test for a machine tool
- In plan and elevation, the tool must move in a straight line parallel to the workpiece’s axis of rotation.
- The axis connecting the centers of the headstock and tail stock must be parallel to the tool travel.
- The cross slide, and thus the tool, must move in a line perpendicular to the workpiece’s axis of rotation.
Instruments used in alignment tests on the lathe
Test Mandrels:
Hardened, precisely ground, and stress-relieved cylindrical rods are used to check the true running of spindles, relative movement of surfaces, and so on.
They are made of high-quality alloy steels that have been heat-treated for maximum stability and wear resistance.
The mandrel’s surface is precision ground and lapped to a fine finish. To improve wear resistance, the surface may be coated with hard chromium.
The diameter of the mandrel is generally kept low to reduce its weight and prevent the supported length from sagging due to its own weight.
Larger diameter mandrels can be hollowed out to save weight, but this should not come at the expense of the mandrel’s stiffness.
Dial Gauges
Dial gauges with magnetic stands and measuring accuracy of 0.01 mm are commonly used for the tests.
The dial gauges must be mounted on a rigid frame with enough bearing area to prevent displacement caused by jerks, vibrations, and so on.
The plunger pressure should be just enough to ensure a positive reading without causing any deflection of the test mandrel or the machine part it is touching.
Straight Edges and Squares
Straight edges and squares for the tests should ideally be made of cast iron or steel.
They must be of robust design, suitably ribbed, and free of internal stresses in order to perform accurately.
They should have a large enough bearing area and a tight tolerance with a squareness of the order of 0.0I mm.
Spirit Levels
Precision is required for spirit levels used to test the flatness of surfaces.
Levels with a sensitivity of 0.03 – 0.06 mm per meter are typically recommended.
The base’s length should be as long as possible, preferably not less than 200 mm.
There are two types of spirit levels: horizontal spirit levels and frame levels.
The frame level is a square-sided frame with spirit levels mounted on the base.
The block square is used to test the flatness of beds and columns in horizontal and vertical planes.
An ordinary spirit level and a try square can be used in the absence of a block square.
Autocollimator
Autocollimators can serve as very sensitive to horizontal, vertical, or inclined planes.
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