What is a bar feed finger?

The bar feed finger is an important part of a bar turning machine because it enables the continuous and automatic production of turned parts with medium to high batch quantities. Its function is to feed the machine tool until the loaded bar is exhausted and completely consumed.

How a bar feed finger works.

The operation of a pusher clamp is based on a principle that utilises the difference in forces.

The feed finger is designed taking into account the mass rotated in the lathe during machining. Once cut, the sliding load is performed taking into account the type of material, specific weight and size of the bar. This sliding load during operation of the machine being machined is much lower than the clamp force of the bar gripper holding the workpiece during turning. During this phase, the gripper slips back and has less pressure on the bar and retracts, preparing to advance the bar for the next workpiece.

When the collet opens, being open it exerts no force on the bar.

At this point, the sliding load of the bar pusher pushes the bar forward and prepares the lathe for the next machining operation.

How the sliding load of a feed finger is adjusted.

The feed finger is constructed using a high-quality steel that undergoes special heat treatment during manufacture. This special steel works by means of a specially created sliding load force in order to advance the bar at the end of each work cycle.

How to check the sliding load of a feed finger.

To check the sliding load of a feed finger, one must first know the theoretical load it should have.

The figure shows a diagram for determining the slide load force of the feed finger.

By inserting a rod bar into the feed finger, we are going to exert a force until the rod retracts into the feed finger. By using a dynamometer during this operation, we are going to check exactly how many daN were required to exert the retraction of the rod bar in the feed finger.

This check can be carried out under a hand press, drill press, lathe, by resting the clamp's mounting surface against a wall and exerting pressure on the bar at the opposite end (fig.2).