What are centering indicators?
Centering indicators are used to indicate or find the centre of a spigot or bore. This instrument is only to be used on holes which are circular (round). Traditionally, centering indicators are used on manual machines; on CNC machines, a 3D sensor would be more appropriate and will provide a higher degree of accuracy.
The unit consists of a dial readout on a metal body. Above this body is a round shank which will be clamped into the machine spindle. Below the body is the feeler or probe which will spin to determine the centre of the hole. In operation, only the feeler will rotate, with the metal housing and dial remaining still for reading off. This is held in position using a torque arm or held by hand.
Centering indicators are usually supplied with different feelers, with some being straight (for internal indicating) and others curved at the tip end (for external indicating). There are also small hole feelers for smaller internal holes.
How do you use centering indicators?
First, the user would set up the indicator in the machine spindle. This can be attached directly into the spindle or using a chuck like a scroll or power chuck. To operate the unit, the user would spin the machine spindle. Doing this will rotate the feeler and make the dial move.
What the user will see is the dial moving backwards and forwards whilst the indicator finds the centre of the hole. As it gets closer to this, the movement will be less. Once the centre is found, the dial will cease movement.
Just one thing to note is that, when finding the centre, you would move the actual job to help find it as opposed to moving the spindle.