Millwright Level 1 Practice Exam

What should the lip relief (clearance) angle of a drill be?

1. 0-5 degrees

2. 5-8 degrees

3. 8-12 degrees

4. 12-15 degrees

The correct answer is: 8-12 degrees

The lip relief angle, also known as the clearance angle, is crucial for the efficient operation of a drill. In this context, a lip relief angle of 8-12 degrees is optimal because it supports effective cutting while preventing excessive rubbing against the material being drilled. This range allows the cutting edge to easily clear the material, which is necessary to reduce friction and heat generation, facilitating smoother operation and extending the lifespan of the drill bit. In contrast, a lip relief angle that is too small, such as in the first two options, can lead to increased drag on the bit, causing it to stall or overheat. Similarly, a larger angle, like the last option, may result in insufficient support for the cutting edge, leading to premature wear or instability during drilling. Therefore, the recommended range of 8-12 degrees strikes the right balance for optimal drilling performance.