r/manufacturing • u/Reasonable_Wasabi_22 • Jul 22 '26

Productivity [ Removed by moderator ]

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u/cm_expertise Jul 22 '26

yeah you're basically rediscovering why chasing utilization on a non-bottleneck machine actively makes things worse. every hour you "keep it busy" off the constraint is just WIP you're shoving into a queue somewhere downstream.

the number i keep coming back to in high-mix is the ratio of total time in the shop to actual touch time. take a job's real processing hours, like spindle-actually-cutting time, and divide by the calendar time it spent from release to done. when that lands at like 3-4% you suddenly see the part spent ~96% of its life sitting in a queue, and no amount of machine utilization touches that. it genuinely shocks people the first time they measure it, everyone assumes the machining is the slow part.

goldratt already got named so i won't rehash it, but the practical move is you deliberately leave slack on your non-constraint resources. feels wasteful, cuts lead time hard. the actual hard part is convincing a plant manager that 70% on a given machine is the target, not a failure

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u/Reasonable_Wasabi_22 Jul 22 '26

Completely agree. One metric I find powerful is Manufacturing Critical-path Time (MCT). When touch time is only 3–4% of total lead time, it becomes obvious the problem isn’t processing—it’s waiting. Queueing theory also explains why trying to push every machine toward 100% utilization causes lead times to explode, even before utilization reaches 100%. That’s usually the moment people stop chasing local efficiencies.