What Is an Idle Gap in a Schedule?

An idle gap is a stretch of unused time on one machine instance between the end of one job and the start of the next on the same day: capacity that could be running but has nothing booked to it. The idle-gap check flags any gap larger than half an hour between two consecutive bookings on the same work center, instance, and date, so the planner can see where the plan left a machine sitting. Unlike a collision or an inversion, an idle gap is not impossible, so it is reported as a warning: a prompt to check whether the wait is intentional or wasted.

This entry is part of the EDGEBIC glossary; see the manufacturing glossary for the wider vocabulary and the scheduling anomaly definition for the family.

How an Idle Gap Works

Each machine instance runs a sequence of jobs through the day. Between the end of one booking and the start of the next, the machine is either immediately reused or it sits idle. The idle-gap check measures that in-between time. For every pair of consecutive bookings on the same instance and date, it computes the gap between the first job's end and the second job's start.

A small gap is normal: machines settle, operators reset, and rounding leaves minutes here and there. So the check ignores anything up to half an hour and flags only gaps larger than that. The same half-hour threshold colors idle cells in the Job View grid, which keeps the report and the visual plan consistent about what counts as a gap.

The check works per instance, not per work center. A cell with three machines can be fully busy as a whole while one specific machine sits idle for two hours. That idle machine is real wasted capacity, and the per-instance view is what surfaces it. A work-center-level total would hide it inside the busy average.

Why Idle Gaps Appear

Gaps are warnings rather than errors because many of them are legitimate, and telling the two apart is the planner's job.

• Waiting for capacity. The next logical job is booked on this machine but cannot start yet because a competing job holds a shared resource, or the downstream work center is full. The gap is the engine correctly waiting.
• Queue, flow, or transit time. A routing step can carry a deliberate buffer: a queue time before the next operation, a start-to-start overlap, or transit days for outside processing. Any of these leaves the machine idle by design while material buffers, cools, or ships.
• Genuine waste. The allocator advanced past a prior booking to avoid a collision and landed at the next shift boundary, or a partial completion shifted the remainder forward and left the original day's tail unused. These are the gaps worth re-sequencing to close.

The check does not judge which case applies; it surfaces the gap and lets you look. A gap with a queue time behind it is informational; a gap with nothing behind it is an opportunity.

Because idle gaps are warnings, the value is usually in the pattern rather than any single row. One gap on a lightly loaded cell is noise. A cluster of gaps on a bottleneck, the cell that limits the whole plant's output, is a signal that the sequence there is leaving throughput on the table, and closing those gaps directly raises what the plant can ship. Reading idle gaps this way turns the check from a list of complaints into a targeted list of where re-sequencing would actually pay, which is why planners run it against their constraint resources specifically.

A Concrete Example

A machining cell has two instances. The Job View shows instance 1 idle from 10 a.m. to noon on Wednesday, and the anomaly report flags a two-hour idle gap there.

The planner checks the routing for the job that runs after the gap and finds no queue, flow, or transit time on the step. Nothing explains the wait. Looking closer, the earlier job on instance 1 ended at 10 a.m., but the next job was placed at noon to line up behind a predecessor on another work center. Re-sequencing pulls a shorter, ready job into the 10-to-noon window, and the gap closes: instance 1 runs continuously and the cell's effective output for the day rises. Had a queue time on the step explained the two hours, the planner would have left the gap alone as intentional buffer.

How EDGEBIC Flags Idle Gaps

In EDGEBIC, idle-gap detection lives in the Scheduler Anomalies report under the Reports menu, in the capacity-waste category. Run it per job or plant-wide. The summary strip shows the idle-gap chips: green when no machine has an unexplained gap over half an hour, amber when gaps are found. Clicking a flagged row opens the schedule so you can see the two jobs and the gap between them.

Because gaps are warnings, the value is in the pattern, not any single row. A plant-wide run that shows many idle gaps on one bottleneck cell is a signal that the sequence there is leaving output on the table, which is exactly the kind of tuning that lifts throughput. For the flip side (a machine over-booked rather than under-used), see the over-utilization check. For how EDGEBIC keeps constraint machines busy, see how EDGEBIC raises bottleneck utilization, and for the load picture, the work center utilization report.

If the symptom is a recurring, unexplained gap rather than a one-off, the troubleshooting walkthrough for a schedule with idle gaps steps through the diagnosis. For the full catalog of checks, read what the EDGEBIC anomaly checks actually look for.

An idle gap is the schedule telling you a machine had a spare hour. Sometimes that hour is a deliberate buffer and sometimes it is money left on the floor, and the report is how you tell which.