Experimental investigation of thread formation in form tapping

In form tapping, the generation of unfinished thread forms results in the appearance of split crests. An experimental technique is developed to study the nature of split crest formation. Custom tools are modeled after tap tooth geometry to perform the forming process in a vertical milling machine. Single-tooth experiments replicate the initial deformation stages and determine the tap geometry and tapping process parameters that significantly affect ridge size and shape. This method is then expanded to consider two axially consecutive tap teeth and the interaction of consecutive ridges to create the final thread form. It is found that certain tap geometrical characteristics are important to the final thread form and, therefore, determine the size and shape of the resulting split crest.