What is the included angle of a twist drill for hard metal?

The included angle of a twist drill for hard metal is 118°. This angle is specifically designed to optimize cutting efficiency and heat dissipation when drilling into harder materials.

The 118° angle strikes a balance between creating a sharp cutting edge and ensuring sufficient durability and strength of the drill bit. This angle helps in reducing the risk of drill breakage and allows for effective penetration into the material while maintaining chip removal efficiency.

Using a 135° angle, for example, might create a sharper point, which could be beneficial for softer materials but could lead to increased friction and heat when drilling into harder metals. This potential for overheating could result in premature wear of the drill or damage to the workpiece.

Similarly, angles like 90° are generally more suited for specific applications such as making holes in softer materials or for particular types of drilling operations, rather than the hard metals typically encountered in more demanding applications. Therefore, the choice of 118° is widely regarded as the optimal included angle for twist drills used with hard metal, making it the correct answer.