It is acceptable to leave a machine running in which scenario?

• A. When changing tools
• B. When clamping the workpiece
• C. When measuring the workpiece
• D. When touching off on the workpiece

Answer: (D)

The key idea is how safe setup actions are performed and why one of them is done with the machine actively involved in the process. Touching off on the workpiece is a setup step used to establish a precise tool length or zero reference by bringing the tool into contact with the part. During this step the spindle is in use and you carefully monitor the approach, stopping at the moment the contact is made to set the offset accurately. This is why it’s considered acceptable to have the machine running for this task: you need the tool to contact the workpiece to establish the correct reference, and you’re actively supervising the process to prevent a crash. In contrast, changing tools, clamping the workpiece, or measuring the workpiece all require the machine to be idle to avoid unintended movements, tool collisions, or injuries, making running the machine unsafe during those activities.