在整个攻丝工序中,孔的准备是最重要的一步。在这里主要的问题是待攻丝孔的直径太小。为了使螺纹达到一定的强度,不应把孔作得比需要的小,因为把孔径稍稍减小一点就会大大增加驱动丝锥所需之扭矩,从而大大增加丝锥折断的可能性。对任何所需螺纹深度的待攻丝孔的直径,均可按下式进行计算: Hole preparation is the most important step in the entire tapping process. The main problem here is that the diameter of the hole to be tapped is too small. In order to achieve a certain degree of strength of the thread, the hole should not be made smaller than necessary because a slight reduction of the aperture will greatly increase the torque required to drive the tap, greatly increasing the likelihood of the tap being broken. The diameter of the hole to be tapped for any desired thread depth can be calculated as follows: