What is a key feature of a ball end mill?

A ball end mill is specifically designed with a hemispherical shape at the end, which allows it to excel in creating curved surfaces and complex three-dimensional shapes. This design makes it particularly useful in machining applications such as contours, molds, and dies, where curved surfaces are essential.

In comparison to other milling tools, a flat end mill is more suited for producing flat surfaces, making it clear that the ball end mill's unique shape serves a different purpose. The versatility of the ball end mill in generating not just curved but also intricate details in a workpiece makes it a preferred choice in many machining tasks.

Regarding the other options, the misconception that it is used solely for hard materials overlooks the fact that ball end mills can effectively work with a variety of materials, from soft to hard, depending on their construction and coating. Additionally, the statement about operating only at low speeds is inaccurate, as the cutting speed depends on several factors, including the material being machined and the specific machining operation.