从理论上说,底孔的直径应该和螺纹孔的内径相等。但是实践证明,底孔必须略大一些才行,这是由于丝锥在攻丝时每个牙都参加切削工作,金属除被切削刃切削掉外,同时还会被全部刃口挤压出来一部分,这些金属挤向牙顶而使内径缩小。如果底孔和丝锥的沟底之间没有足够的空隙容钠被挤出的金属,那么挤出的金属就会把丝锥和工件卡住面折断比锥。所以在攻丝 In theory, the diameter of the bottom hole should be equal to the inner diameter of the tapped hole. However, practice has proved that the bottom hole must be slightly larger Caixing, which is because the tap tapping each tooth to participate in cutting work, in addition to being cut by the cutting edge of the metal, but also squeezed out all the part of the edge, These metals squeeze the top of the crest and shrink the inner diameter. If there is not enough space between the bottom hole and the bottom of the taps to allow sodium to be squeezed out of the metal, the extruded metal will break the tap and the workpiece catch off the cone. So tapping