Live centers are available with extended points, which provide maximum tool clearance but sacrifice some rigidity, or with shorter points, which offer rigidity but sacrifice some tool clearance. A wide variety of live centers are available. Generally, look for centers that have been designed specifically for your application. CNC heavy duty centers for CNC lathes, spline rolling centers for spline rollers, super accurate centers for grinding, heavy duty and extra heavy duty models for large parts and bull nose centers for parts with large center holes.
Selecting live centers requires a clear understanding of the application's needs. Rpm, work piece weight, tool and tailstock pressure, center hole size, and the need for tool clearance should all be considered carefully. Manufacturers' recommendations for maximum work piece weight and RPM play a key role in center selection. Exceeding limits for a live center is extremely dangerous. When in doubt, consult the center's manufacturer. In general, leave a comfortable margin for both weight and RPM.
Dead centers can be full centers or half centers. Half dead centers have a large cut out removing most of the point. They're typically used for additional wheel clearance when grinding small parts whose diameter is less than that of the dead center. The cut away section provides clearance so the grinding wheel can advance to the part without hitting the center. Full centers have the entire point.
Carbide tips can be brazed to the same steel shanks that are used in steel centers. They are also available as full or half dead centers. In high volume operations carbide centers are preferred, due to the high wear resistance of carbide. When holding highly abrasive or very hard materials, carbide centers outperform steel centers.
A face driver does away with the need to flip the workpiece during the production process and allows for the entire piece to be worked in one operation. In this process the piece of steel is centered in the machine using a live center that locates its point in the center hole on one end of the workpiece. A face driver then uses tailstock pressure to engage the workpiece with its center point which locates the part and provides a consistent axis of rotation. As the machine’s tailstock pressure continues to drive the workpiece against the center point, the axial pressure forces the spring-loaded center point back into the carrier body until the drive pins engage the face of the workpiece, eliminating the need to chuck on the outer diameter. Each pin individually compensates for any irregularities in the face until all pins are fully engaged. This technique removes the chuck jaws from the path of the cutting tool and enables the piece to be worked from end to end, simultaneously cutting production time and increasing concentricity.