During a process improvement effort, the team discovers that machine X is underutilized, but it...

 The theory of constraints (TOC) emphasizes identifying and addressing bottlenecks in a process to improve overall system performance. When a process improvement team discovers that a machine (in this case, machine X) is underutilized but not a bottleneck, the following recommendations apply:

Allow machine X to continue to have idle time: Since machine X is not constraining the overall process flow, keeping it idle ensures that other processes can operate efficiently without unnecessary interruptions. This approach prevents excess inventory buildup and minimizes costs associated with running an underutilized machine.

Do not increase the flow of parts to machine X: Increasing the flow of parts to an underutilized machine would lead to unnecessary inventory buildup and may not contribute to overall process efficiency.

Avoid keeping a backlog of stock available at machine X: Stockpiling inventory at machine X would not be beneficial if it is not a bottleneck. It could lead to storage costs and potential waste.

Do not remove machine X: Removing machine X entirely would be premature and could disrupt the overall process. If it is not a bottleneck, it serves as a backup or support for other processes.

In summary, the team should allow machine X to continue having idle time, focusing efforts on optimizing the true bottleneck(s) in the operation1.

 1 The ASQ Certified Manager of Quality/Organizational Excellence Handbook, Fifth Edition. Sandra L. Furterer and Douglas C. Wood. ASQ Quality Press, 2021. Link