Lights-Out Scheduling
How to plan CNC and FMS cells so they run all night without stopping at 2 a.m. Pallet awareness, setup clustering, tool readiness, and the sequencing discipline that turns unattended hours into shippable parts.
Built with real job shops
Developed alongside discrete manufacturers running 20–200 machines — CNC, fabrication, mixed operations, including Boeing-tier suppliers.
Co-designed with planners
Every concept on this page was pressure-tested against live planners, schedulers, and shop-floor supervisors — not derived from generic SaaS playbooks.
Validated on the floor
Pallet pools, setup clustering, lights-out runs, outside processing, hot jobs — modeled from real machinist workflows, not theory.
What is lights-out scheduling?
Lights-out scheduling is the practice of planning CNC and automation cells — FMS pallet pools, HMC cells, robotic load cells, bar-fed lathes — to run unattended outside staffed shifts. The schedule must guarantee that every operation in the unattended window has its material loaded, tools verified, pallets staged, and programs proven, because no operator is present to fix anything. Done well, it can double or triple effective machine hours without adding labor.
How it works
- •Identify cells capable of unattended runtime (pallet pool, tool magazine, probing, automation).
- •Cluster jobs by fixture family, tool family, and material to maximize uninterrupted run sequences.
- •Pre-stage every tool, pallet, and program required for the entire unattended window.
- •Sequence the longest-cycle, lowest-risk jobs into the unattended block.
- •Verify material on machine, tool life, and probing before releasing the cell to lights-out.
Why it matters
A typical job shop with FMS or HMC pallet pools captures 30–50% of theoretical lights-out hours. The rest is lost to cells stopping mid-night because a pallet finishes, a tool runs out of life, or a program needs intervention. Properly scheduled lights-out is the cheapest capacity in the building — it requires no new machines, no new operators, no new floor space.
How Skody does it
Skody models pallets, fixtures, tool life, and probing as first-class constraints. The scheduler builds lights-out windows by clustering compatible jobs, verifying readiness before release, and conservatively sequencing the unattended block. Cells that previously stopped at 2 a.m. routinely run through to first shift.
Why lights-out scheduling is the most underserved niche in production planning
Almost every APS and ERP scheduling module treats CNC capacity as a flat hourly bucket: 24 hours of available time per day, allocate against demand. That model produces a schedule that looks reasonable on a Gantt chart and fails completely on a real automation cell.
Lights-out runtime is not 24-hour capacity. It is a different mode of operation with different constraints: pallet identity matters, tool life matters, probing matters, the sequence within the unattended block matters far more than the sequence during a staffed shift. Most planning systems do not model any of this — so most shops with the equipment to run lights-out are not capturing the benefit.
The gap is the largest underutilized capacity lever in modern discrete manufacturing. A shop with ten capable cells can typically add the equivalent of three full machines to its weekly output without buying anything new — if the scheduling system models lights-out properly.
Pallet awareness: the resource the ERP does not see
In a horizontal machining center pallet pool or FMS, the pallet is the schedulable resource — not the machine. The machine has 24 hours of capacity per day; the question is which pallets, mounted with which fixtures and parts, the cell can cycle through during those hours.
A pallet-aware scheduler tracks:
- Pallet identity (which physical pallet is which).
- Fixture mounted on each pallet.
- Parts currently set up on each pallet.
- Pallet queue position in the cell.
- Pallets currently being set up off-cell.
Without this, the scheduler can release "16 hours of work" to a cell whose pallet pool can only physically cycle through 10 hours of work before requiring a pallet swap. The unattended window stops at 2 a.m. when the last loaded pallet finishes.
Setup clustering: sequencing for the unattended window
Setup clustering for lights-out is the deliberate grouping of jobs that share tools, fixtures, and material so that the unattended sequence requires the fewest possible interventions. The goal is not optimal staffed-shift sequencing — it is the longest possible run with the currently loaded toolset.
Three clustering rules:
- Tool-family clustering. Jobs that use the same tools, in the same expected wear profile, are sequenced together so the magazine does not run out of any critical tool mid-night.
- Fixture-family clustering. Jobs on the same fixture or compatible fixtures are sequenced consecutively to avoid pallet swaps that require operator attention.
- Material-class clustering. Aluminum runs together, stainless runs together, exotic alloys run together — to keep coolant chemistry, chip evacuation, and cycle-time assumptions consistent.
Unattended runtime planning
The unattended window in a typical North American job shop is roughly: 6 hours overnight on weekdays (10 p.m. to 4 a.m.), plus 48 hours over the weekend. Across a five-day week, that is 30 + 48 = 78 hours of unattended capacity per cell, on top of the 80–120 hours of staffed capacity.
Properly scheduled, those 78 hours can run at near 100% spindle utilization on long-cycle work. Improperly scheduled, they run at 30–50% as cells stop at random points in the night for missing tools, full chip conveyors, broken probing, or finished pallet pools.
The difference is not the equipment. It is the schedule. Two shops with identical FMS cells can have vastly different lights-out capture rates based purely on how their scheduling model handles the unattended window.
Tooling readiness: the lights-out release checklist
Before a cell is released to lights-out, the scheduler must verify a concrete readiness checklist for every job in the unattended window:
- Tool life. Each cutting tool has enough remaining life for its expected use in the window — with margin for one re-cut.
- Tool presence. Every required tool is physically loaded in the magazine and in the correct pocket.
- Probing routines. All probing programs are validated and the probe stylus is in working condition.
- Material on machine. Stock is loaded on the pallet or bar in the feeder for every queued operation.
- Program proven. Every program in the window has run successfully at least once with the same setup.
- Coolant and chip evacuation. Tanks are full, chip conveyor and bins are clear.
A schedule that releases the cell without verifying every line of this checklist is gambling. The lights-out cells that run reliably are run by shops that treat the checklist as non-negotiable.
Overnight sequencing: lowest-risk last
The sequence inside the unattended window is itself a design choice. The principle: order the jobs so that if the cell fails partway through the night, the failure happens as late as possible and as recoverably as possible.
- Highest-confidence jobs first. Proven programs, familiar tools, current setups.
- Pallet-balanced. Alternate pallets so the pool drains evenly, not in a way that strands work on a single fixture.
- Longest cycles last. If a long-cycle job fails late, less wall-clock time is lost than if a short job fails early.
- No new programs in the dark. First runs are always staffed; the unattended window is for proven work.
A real overnight sequence
A 16-pallet FMS cell with eight HMCs ends second shift at 10 p.m. with the magazine loaded for a mixed run of titanium brackets and aluminum housings. The lights-out window runs 10 p.m. to 4 a.m. — six hours.
Naive sequence: jobs released in due-date order. The third job (a new titanium bracket program) requires a probing routine that has never been run successfully. At 11:47 p.m. the machine alarms on a probe error and sits idle until first shift. Captured runtime: 1 hour 47 minutes of six.
Pallet- and clustering-aware sequence:proven aluminum housings run first (low risk, fast cycle). Then proven titanium brackets clustered to share the same fixture family. The unproven titanium program is excluded from the lights-out window and re-scheduled for first shift tomorrow. Captured runtime: 5 hours 50 minutes of six.
Same cell, same machines, same operators, same shift end. Four extra spindle-hours per cell per night, multiplied across eight machines, multiplied across five weeknights, is 160 spindle-hours per week — without any new capital investment.
How Skody schedules lights-out
Skody is one of the few schedulers that treats pallets, tools, and lights-out runtime as first-class constraints rather than afterthoughts. The engine models pallet identity, tool life, probing readiness, and material staging, and produces an unattended window release checklist for every cell every night.
- Pallet-aware solver. Cells are scheduled by pallet, not by machine hour.
- Setup clustering by default. Tool, fixture, and material families are recognized in the solver and clustered into the unattended block.
- Lights-out readiness gate. The cell is not released to unattended runtime unless the checklist passes.
- Conservative sequencing. Unproven jobs are pulled out of the window automatically and rescheduled to staffed hours.
Frequently asked questions
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