Method for rolling tapered threads on bars

Abstract

A machine and process for forming a high strength precision bar joint and more particularly for forming rolled tapered threads on a bar end such as the tapered end of a reinforcing bar used in concrete construction. Such machine and process employs opposed oppositely rotating die disks which have conical opposed die surfaces. A thread form die is provided on the conical die surfaces in the form of thread form spirals which bear against the opposite sides of the tapered bar surface as the die disks rotate. The die surfaces include opposed recesses into which the bar end is inserted. The bar may be held for rotation aginst a stop as the die disks oppositely rotate. Alternatively the bar end may be held against rotation and the die disks orbited around the bar end as the die disks oppositely rotate. A tapered surface is formed on the bar end prior to roll forming of such threads as by hot or cold forging or by cutting. The bar is held by a transfer vice for transfer from the tapered surface forming operation to the thread rolling operation to ensure that the tapered surface is properly centered while the threads are formed.