Iron Wire,Iron Mesh,Wire Iron,Thick Iron Wire HENGSHUI YUZHENG IMPORT AND EXPORT CO., LTD. , https://www.yuzhengnails.com Before drilling with a twist drill on the machining center, we use the drill bit shown in Figure 1 or Figure 2 to pre-drill the locating hole. The advantages are as follows: (1) The rigidity of the drill bit is higher than that of the twist drill, and the pre-drilling locating hole can be improved. Pitch accuracy. (2) Pre-machining the chamfering of the hole, and the twist drill does not need to be chamfered after drilling, which improves the efficiency.