Alignment of Spindle Axis with Bed

Alignment of Spindle Axis with Bed

Alignment of Spindle Axis with Bed -In many machine tools, lathes in particular, the accurate alignment of the axis of rotation of the headstock spindle with the bed and line of centres is of great importance. In the test charts mentioned, the methods of check specified for these elements utilise mandrels and dial indicators.

The parallelism of spindle axis and bed can, for instance, be checked with an accurate mandrel having a taper which fits into the spindle and a parallel portion which can be clocked from the bed. For such tests, the over hang of the mandrel should not produce appreciable sag, mounting of the dial indicator should have sufficient rigidity, etc.

This class of work can be best undertaken using autocollimator with a little auxiliary equipment well as two plane reflectors, one of which has its opposite faces parallel and polished, and a suitable mount to rest on the bed.

One of the reflectors is set on the machine spindle 10 a plane normal to its axis; it is usually convenient to mount this on the face plate when one is fitted.The autocollimator is set on the axis of the machine, and the reflector is adjusted until there is no movement of the reflected image as the spindle is rotated.

The doublesided parallel reflector fitted to the mount is then set on the bed, the height of the reflector being adjusted so that its centre lies approximately on the machine axis.

The provision of an adjustable mount for this reflector also greatly facilitates its setting, as it has now to be set so that there is no change in auto collimator reading when the mount is turned end for end, and the reflection is obtained from the opposite side of the reflector.

When the reflector is adjusted for no change of reading on reversal, or the mean of the two readings is taken, such reading represents true squareness to the surface of the bed and to its aides, if these are also being checked. Comparison of this reading with that obtained from the spindle axis indicates the error in alignment between the bed and the spindle.

A sensitive autocollimator of the micrometer type is best for this type of work unless only approximate results are required. At least three readings should be taken on both reflectors, on the faceplate and the bed mount, turning through 180° between each, in order to ensure that no movement has taken place. This is, of course, merely the standard practice of repeating a zero or initial reading after taking other readings.

Testing of Parallelism of Spindle and Bed