Thread cutting process Blind hole Blind hole shearing process 2 The tool begins to reverse The chips remain where they are for the time being The

Thread cutting process Blind hole Blind hole shearing process 2. The tool begins to reverse. The chips remain where they are for the time being. The reverse torque at this point is virtually zero. 1. The tap has been cutting and now comes to a stop. At this very moment, all cutting edges in the chamfer are still in the process of forming a chip. 3. The chips come into contact with the trailing land of the tap. The reverse torque now increases sharply. The chip has to be shorn off. As the chamfer of the tap has a clearance angle and the conical chamfer withdraws from the thread axially when it backs out of the hole, it is inevitable that the attachment point will no longer be directly at the root of the chip. For this reason, the chip would require a certain amount of stability (thickness) to be cut. As a result, taps having a long chamfer are not suitable for use in blind hole cutting because of their greater chamfer angle. If a tap such as this were used, there would be a risk of the too thin chip not being shorn off, but simply flattened and becoming trapped between the chamfer and the thread. This could lead to galling in the chamfer and, in extreme cases, tap breakage. 4. The chip has been shorn off and reverse torque decreases to just the friction between the guide portion and the cut thread. Blind hole Torque curve during the blind hole thread tapping process Please note The shearing of the chip in the blind hole thread presents a particular problem. If the chip becomes too thin, it simply flattens and can no longer be cut through. Instead, it becomes trapped between the component and chamfer flank face. Long chamfers (form A, D or B) and high chamfer clearance angles are therefore unsuitable for tapping blind hole threads. sharp increase in torque zero and reversing starts D 443 Technical information threading WALTER PROTOTYP Application information