Fullering is a forging method used to reduce the diameter of a bar while simultaneously increasing its length. It is commonly used to create a taper in the workpiece or to refine the shape of the bar. This process is achieved by using a specially designed tool called a fuller.

The fuller is a rounded or wedge-shaped tool that is typically made of high-strength steel. It is used to strike the workpiece and apply compressive forces to the material, which results in the reduction of the diameter. The fuller is usually held by a blacksmith or a forging machine, and it is struck with a hammer or a power hammer to deform the workpiece.

The fullering process involves several steps:

1. Marking: The desired taper or reduction in diameter is marked on the workpiece. This serves as a guide for the blacksmith or machine operator during the forging process.

2. Heating: The workpiece is heated to a temperature that allows it to be easily deformed. This temperature is typically above the recrystallization temperature of the material, which helps to reduce the force required for forging.

3. Positioning: The workpiece is positioned on the anvil or in the forging machine, and the fuller is aligned with the marked taper or reduction area.

4. Striking: The fuller is struck with a hammer or power hammer, exerting compressive forces on the workpiece. The repeated blows cause the material to flow and deform, resulting in a reduction in diameter and an increase in length.

5. Cooling: After the desired shape has been achieved, the workpiece is cooled to room temperature. This helps to retain the new shape and prevent any further deformation.

The fullering process is commonly used in various industries, including blacksmithing, metalworking, and forging. It is a versatile method for shaping bars and can be used to create complex shapes and designs. Additionally, fullering can be combined with other forging techniques to achieve specific results, such as creating a stepped or tapered bar.