After many experiments, a new type of tap was designed as shown. When making, open a guide cylinder with a chip flute at the front end of the tap (or grind it on the original tap) with a diameter slightly smaller than the diameter of the threaded bottom hole. Example: M10 thread, guide cylinder diameter d=φ8.5_(-0.16)~(-0.10)mm, L_2=5mm. When tapping, the guiding cylinder enters the bottom hole.
New tap