What Is a Centering Bar?
A centering bar is a jig that detects the origin position of a machine tool on a flat surface with a high accuracy.
The centering bar is held by the machine tool and moved slowly toward the edge of the workpiece while the spindle is rotating, until the eccentricity of the centering bar, which is in contact with the workpiece, is completely eliminated. The position where the runout is completely eliminated can be defined as the origin. This is an important item because the accuracy of the origin is directly related to the accuracy of machining.
Origin positioning by the touch sensor is also available. While touch sensors are convenient, it takes time and effort to compensate for any abnormality that may occur.
Uses of Centering Bars
Centering bars are used when machining with lathes, milling machines, and other processing machines that require high accuracy.
On a lathe, the chucked centering bar is brought close to the rotated material, and the origin position is determined by the runout of the chucked material. If centering is required again after machining, the use of a dial gauge is recommended.
On the milling machine, the table is flattened with an oil wheel, and then the centering bar is set on the collet. It can be adjusted visually by bringing it close to the material. If eccentricity is observed, the levelness can be adjusted using a copper plate or arrow.
Principle of Centering Bars
When used on NC/MC machine tools, the shank of the centering bar is attached to the milling chuck or drill chuck, and the centering bar is slowly brought close to the workpiece and rotated so that the measuring element is eccentric. When the workpiece is slowly brought closer to the measuring element while it is rotating, the eccentricity becomes smaller and the runout of the measuring element is eliminated, and the workpiece is adjusted so that it is completely stationary. When the workpiece is moved slightly from the stationary state and comes into contact with the workpiece, the measuring element moves along the measurement surface. This position is the reference position, considering the diameter of the measuring element.
Since the centering bar is made of metal, it will become magnetized and cease to function after prolonged use. It must be replaced after a certain period. Since it is classified as a consumable item, a non-metallic material with excellent durability is ideal.
The accuracy of the origin is an important item because it directly affects the accuracy of processing.
Depending on the application, materials are selected from stainless steel, non-magnetic special steel, ceramic, chrome molybdenum steel, etc.
In addition to coordinate detection, it is used to measure the diameter of a circle and the distance between two points.