Method for machining and improved modified threaded collar

Abstract

Disclosed is a method directed particularly to improving a modified threaded buttress collar. The method is also of value with any internally threaded member having a seal ring groove therein. The method specifically deals with the removal of the feather edge thread created when a seal ring groove is placed within an internally threaded member. Such groove usually provides residence for a seal ring. When the groove is placed in the internally threaded member there is created a feather edge thread immediately adjacent the groove. This feather edge thread is easily deformable and can create severe galling problems within the coupling. The feather edge is removed, preferably, in stepped fashion utilizing a machining tool such as a grooving tool within a computer numerically controlled lathe. The grooving tool is set such that as the coupling turns in the lathe, the movement of the grooving tool matches the pitch and helix of the threads and the speed of the lathe. However, the grooving tool is offset such that it is placed on a collision course with the thread. The groove allows some running time for the grooving tool to be properly positioned for the specific thread pitch and helix. The feather edge is removed in several passes, each being deeper than the last until, ultimately, the feather edge is removed to a depth equal to the depth of the finished threads.