Which type of machining tool has one cutting edge and is primarily used on lathes?

The type of machining tool that has one cutting edge and is primarily used on lathes is the single-point cutting tool. This tool is specifically designed for tasks such as turning, which involve removing material from a rotating workpiece. The single-point design allows for precise control over the cutting process, making it ideal for creating specific shapes and surfaces on cylindrical workpieces.

Single-point cutting tools can be used for various operations, including shaping, facing, and threading. The simplicity of having just one cutting edge enables the tool to focus on a specific area of the workpiece, allowing for greater accuracy in cutting depth and surface finish. This characteristic makes single-point cutting tools integral to lathe operations, as they can be adjusted easily for different machining requirements.

In contrast, multi-point cutting tools have multiple cutting edges and are used for operations like milling, where a broader surface needs to be machined simultaneously. Drills are specifically designed for creating holes and have a different structure and application. Milling tools, used in milling machines, typically feature multiple cutting edges also designed for producing flat surfaces or complex shapes on a workpiece. Thus, the unique design and application of the single-point cutting tool is what establishes it as the correct answer in this context.