A true alternate work center is a capacity-aware fallback that replaces a routing step's primary machine when it can finish the job sooner, chosen before scheduling begins by comparing projected completion on each candidate. It is the flexible-routing mechanism: instead of pinning every operation to one machine, you name backups, and the engine picks the machine that gets the work done fastest given real load. A true alternate uses its own run time, so a slower backup is planned honestly with its own longer hours.
EDGEBIC by User Solutions resolves true alternates in a pre-scheduling pass. This article defines the term and how the swap is decided. The full resolver behavior and worked cases are in how EDGEBIC handles parallel and alternate work centers.
How It Works
You list one or more true alternates on a routing step, each with its own run time. Before any capacity is allocated, the resolver runs. It projects completion for the primary and every alternate, factoring each machine's speed and its current queue depth, then swaps the step to whichever candidate finishes earliest.
The swap is complete. Once an alternate wins, the step is scheduled on it exactly as if it had always been the primary, using the alternate's own run time rather than the primary's. A backup that runs slower carries its longer hours into the plan.
A selection strategy governs the choice. The default is earliest completion, which minimizes each job's lead time and will move work to whichever machine finishes soonest. An alternative is primary-first, which tries the designated primary and spills to a backup only when the primary has no capacity on the target date. Earliest completion suits shops where cycle time rules; primary-first suits shops that want predictable, consistent routing. Whether the engine applies that strategy at all, or defers to machine choices you supply by hand, is set by the run's alternative selection mode.
A Concrete Example
Think of an oven step written as "use Oven A, but if it is busy, use Oven B, which runs twenty percent slower." That is a true alternate. Now take three CNC machines: CNC-1 is the primary, CNC-2 and CNC-3 are true alternates with their own run times. CNC-1 is fully booked Monday, so a new job would queue behind existing work and finish Wednesday. CNC-2 can start Monday and finish at 16:00 with its six-hour run. CNC-3 could start Tuesday.
The resolver compares projected completion: Wednesday on CNC-1, Monday 16:00 on CNC-2, Tuesday on CNC-3. CNC-2 wins. The step is swapped to CNC-2, uses CNC-2's six-hour run time, and schedules Monday 08:00 to 14:00, finishing two days earlier than it would have on the busy primary. The slower backup lost, the available one won, and its own hours were planned correctly.
What the Swap Preserves
Once an alternate wins, the swap is thorough. The step is re-pointed to the winning machine, and any parallel machines that were attached to the old primary are re-pointed too, so the whole operation moves together rather than leaving pieces behind. The winning machine's own run time is used throughout, so the plan reflects that machine's real speed rather than the primary's.
The choice is also stable through rescheduling. A step that has already started stays on the machine it started on, because completed and in-progress work is never moved. Only a not-yet-started step re-shops across its alternates on the next run, comparing projected completion against current load. That means the resolver relieves a busy primary without disturbing work already underway, and a job that jumped to a backup last week is free to jump back to the primary this week if the primary is now the faster finisher. The alternate is a live decision recomputed against reality, not a one-time reroute frozen into the routing.
How EDGEBIC Uses It
True alternates surface wherever a routing step names backup machines. The engine resolves them before scheduling, reports which candidate won and why, and then schedules the step on the winner. Because the choice is capacity-aware, a fast machine buried under a backlog can lose to a slower one that is free, which is exactly how a planner would decide by hand.
A work center group is a natural extension of this idea: instead of naming backups on each step, you point the step at a pool of interchangeable machines and the engine explodes it into a primary plus true alternates automatically. See what is a work center group for that model, the manufacturing glossary for related terms, and how to set a true alternate with a speed factor for the configuration steps.
Expert Q&A: Deep Dive
Q: Our primary CNC is always the bottleneck and jobs pile up behind it while two other CNCs sit half-idle. How do true alternates help?
A: List the two idle CNCs as true alternates on that routing step, each with its own run time. Before scheduling, the engine projects completion on all three: the primary queued behind its backlog, and each alternate against its own lighter load. If an alternate finishes sooner even at a slower speed, the engine swaps the step to it and schedules there as if it had always been the primary. In a real case a job queued behind two days of work on the primary jumped to an alternate and finished the same Monday, two days earlier. You keep the primary as the preferred machine and let the engine relieve it only when a backup genuinely wins.
Q: If I add a true alternate, will the engine scatter my jobs unpredictably across machines?
A: Only if you leave it on the default earliest-completion strategy, which optimizes each job's lead time and will move work wherever it finishes soonest. If you want predictable routing, set the selection strategy to try the primary first and spill to alternates only when the primary has no capacity on the target date. Then jobs stay on their preferred machine until it is genuinely full, and the alternates act as pure overflow. Choose earliest completion when cycle time matters most, and primary-first when consistency and operator familiarity matter more.
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