How to Select Dead Centers
Dead centers are used to hold or support a workpiece in a lathe or other machine tools - often between the headstock and tailstock. Live centers revolve with the work, while dead centers are stationary. Dead centers are generally available in two types, standard dead centers and half dead centers. Standard types have a fully conical-shaped point that mates with the work piece. Half dead centers are similar, except about half of the mating tip has been removed. Custom and proprietary centers types are available, but these styles are somewhat rare.
Dead centers are available with a wide degree of points, which are the portions of the center, which pierce or hold the work piece. Common point types include standard points, bull nose points, long points, pipe points, and tracer points. Standard points have a constant point angle and have no special attributes such special tips or hardening. Bull nose points have flat faces, which allow the work piece to sit at least halfway up the point. Long points have a small straight diameter extension near the point that allows for better tool clearance. Pipe points are specialty holders used with tubing, piping or other thin walled pieces. Tracer points have a standard angle tip which then changes to a shallower angle on the remaining portion of the point. For instance, the tip angle is about 60 degrees and the rest of point angle is 30 degrees.
In addition to particular point types, dead centers may have the following features, which allow them to perform their duties more efficiently, or to engage in specialized applications. Some of these features include carbide tips, high-speed engagement centers, super accurate centers, chucking centers, and changeable or replaceable centers. Carbide-tipped dead centers are generally longer lived products, as carbide tends to resist wear better than most other materials. Additionally, carbide tipped points may be used in high-speed applications. High-speed tips are capable of operating at high speeds. Generally speaking they can handle speeds in excess of 6,000 rpm. Super accurate centers are used in precision grinding applications. Chucking centers have a multi-jawed chuck into which the work piece may be inserted. These devices offer greater control than simple points, although they tend to be slower in processing lines since each item needs to be gripped, tightened, and then released instead of simply pierced and released. Changeable points allow on the fly replacement of dead center points. This can save time and money since the entire dead center does not have to be replaced.