What happens to the surface finish if the tool is worn?

When a tool becomes worn, its ability to effectively cut the material diminishes. As tools wear down, the cutting edges can become dull, which results in increased friction and heat during the machining process. This can lead to a rougher surface on the workpiece because the tool may not be able to remove material as cleanly or accurately as it did when it was new.

Additionally, worn tools may lead to chatter, which is vibration during machining that further deteriorates the surface finish. Therefore, the overall quality of the surface finish tends to decrease as the cutting tool wears out, making the chosen answer accurately reflect the consequence of using a worn tool in CNC milling.