ABSTRACT
with the normal drilling process. The hole is made by rotating a carbide steel conical tool bit at high speed and pressure against the tube surface. This rapidly builds up sufficient local heating to soften the material and allows the tool to be forced through the tube wall and swage the material predominately on the inside of the parent material in the form of a truncated hollow cone on the inner surface. A greater depth of material for the production of threaded holes than that provided by the parent metal (Fig. 1) is therefore produced.
