Cutting tap with opposite-sheared screw chip grooves for threading in fiber-reinforced composites

The field of application of products made of fiber-reinforced composites (FRC) is expanding every year. Despite the fact that such products are often manufactured in near-net shape, it is currently not possible to avoid using cutting completely. Specificities of FRC structure and component parts require that the search for specialized solutions for their machining have to be performed. In addition to traditional operations, such as milling and drilling, there is a need to tap threads in the composite workpieces. However, standard threading tools do not provide the required quality of the machined thread. Tools for machining FRC workpieces need to have significant design differences from traditional tools in order to ensure rational cutting conditions on cutting wedges. Thus, the authors have developed the design of the special tap with an even number of counter-directed screw chip grooves. The specificity of this tap is the fact that when grinding the tap thread areas of teeth surfaces are additionally cut off from even and odd feathers in a checkerboard pattern. Therefore, it is possible to exclude from the machining the sections of cutting edges with unfavorable cutting conditions. However, the proposed design specificity requires the development of specialized technological solutions for effectively manufacturing of the tap. The backing-off along the thread profile is one of the operations which are difficult to realize. Thus, the paper presents the main design parameters of such taps and, in addition, the calculation of the maximum diameter of the abrasive tool for tap backing-off along the thread profile.