Thread Forming Screws

There are various methods used in the production of creating threads, one of these is known as thread forming. As opposed to thread rolling which creates a thread on the external diameter of a bar, the forming of a thread takes place on the interior of a bar, i.e. a hole or bore. Thread forming is performed by using a roll tap or fluteless tap. These taps closely resemble cutting taps but have no flutes and as such do not cut. The thread is formed by usually three lobes which are spaced equally around the taps diameter. It must be said that the hole size for thread forming is different from the hole size drilled when using a cutting tap. The hole is drilled larger because a slightly undersize hole will cause the tap to break due to the high pressure of the forming process. Correct whole sizing is extremely important, and the use of a chart or tables should be employed. Lubrication of the operation is also important because of the frictional forces involved; therefore lubricating oil is used instead of coolant or cutting fluid. The production rates are normally three to five times faster than thread cutting.