丝锥攻丝及板牙套丝时,都会发生“胀牙”现象,使螺纹的齿顶被“挤高”一些。因此,攻丝前钻的底孔,应稍大于成品螺纹的内径;套丝前的工件外径,则需比成品螺纹的外径小一些。攻丝前钻底孔的钻头直径,有关的金属切削手册中已给出经验公式,并将计算结果列成了表列,供生产中使用。但套丝前工件的外径尺寸,我国现行的各种金属切削手册中,还没有提出简易的计算方法来。这是生产中需要解决的一个问题。合理地确定这一尺 Tap tapping and die set threading, there will be “bulging teeth” phenomenon, so that the top of the thread is “crowded” some. Therefore, the hole drilled before tapping should be slightly larger than the inner diameter of the finished thread. The outer diameter of the workpiece before threading is smaller than the outer diameter of the finished thread. Drill diameter before drilling the bottom hole, the relevant metal cutting manual has been given empirical formula, and the calculation results into a list for use in production. However, the outer diameter of the workpiece before threading size, China’s current variety of metal cutting manual, has not put forward a simple calculation method. This is a problem to be solved in production. Reasonably determine this rule