A shipping buffer is protected time placed after a bottleneck operation so that variation in the downstream steps does not push the customer due date. It is the third of the three Theory of Constraints buffers, and it guards the promise rather than the constraint. Once a job clears its bottleneck, the shipping buffer absorbs any slip in the finishing steps before delivery.
EDGEBIC by User Solutions sizes the shipping buffer automatically when a job is anchored on a constraint. This article defines the term and shows how it holds a committed date.
How It Works
When a job anchors on its bottleneck, the routing splits into an upstream half that feeds the constraint and a downstream half that runs after it. The shipping buffer occupies the gap between the end of the downstream work and the promised due date. The engine schedules the post-constraint steps to finish not at the due date, but at the due date minus the buffer. That leaves a cushion of protected time in front of delivery.
Buffer sizes are proportional, not fixed. The shipping buffer is a fraction of the remaining downstream lead time, roughly 15 percent in the current implementation, with a minimum floor so a short path still gets real protection. A longer downstream path carries a larger buffer because it holds more accumulated risk on the way to the dock.
Three buffers work together. The constraint buffer protects the anchor from upstream variation, the feeding buffer targets the single step that feeds it, and the shipping buffer protects the due date from everything after the anchor.
A Concrete Example
Think of a dinner party. The roast is the constraint: it comes out of the oven at a fixed time and you cannot rush it. But guests do not eat the moment the roast is done. It has to rest, be carved, be plated, and reach the table. If you plan for guests to sit down the instant the roast leaves the oven, one slow carve makes dinner late.
A shipping buffer is the deliberate gap you leave between the roast coming out and the guests sitting down. In a real job, take a routing anchored on a heat-treat oven with deburr, inspection, and packing after it. The engine sizes the shipping buffer at about 15 percent of that downstream path and schedules the finishing steps to complete that much earlier than the ship date. Now if inspection runs an hour late, the buffer absorbs it and the order still ships on the promised day.
How EDGEBIC Uses It
The shipping buffer appears whenever you enable buffer calculation on an anchored job. The engine reports its size alongside the constraint and feeding buffers, and shows the finishing steps scheduled to land before the due date rather than on it. You can see exactly how much protected time sits between the last operation and the promise.
Because buffers are re-sized on every run, the shipping buffer stays honest through rescheduling. Completed work is never moved, and the buffer is recomputed against the downstream time that genuinely remains, so a job that is halfway done carries a buffer matched to the steps still ahead of it. A committed date backed by a live shipping buffer is far more reliable than a raw earliest-finish estimate.
The shipping buffer is one part of the constraint story. The manufacturing glossary covers the related terms, and the full buffer arithmetic lives in how EDGEBIC does anchor scheduling. If your shop has not yet found its constraint, start with the Theory of Constraints.
Expert Q&A: Deep Dive
Q: Our jobs clear the bottleneck on time but still ship late. What is going wrong?
A: The constraint is protected but the tail end of the routing is not. After a job clears the bottleneck it still has finishing steps, inspection, packing, and paperwork, and any of those can slip. Without a shipping buffer the schedule assumes those steps run to the minute, so a two-hour delay in final inspection becomes a two-hour late shipment. A shipping buffer inserts protected time between the last downstream step and the promised date. In a job anchored on a heat-treat oven, the buffer after the oven means a slow deburr or a held inspection is absorbed rather than passed straight through to the customer. The fix is to protect the ship date, not just the constraint.
Q: Is a shipping buffer wasted time that just makes my quoted lead time longer?
A: It makes the committed date honest, which is the opposite of waste. A raw earliest-finish estimate assumes every downstream step runs perfectly, so it quotes a date the plant misses whenever anything varies. A shipping buffer sized at roughly 15 percent of the downstream path builds the real-world variation into the promise, so the date you give the customer is one you actually hit. You can quote the aggressive no-buffer date and be late often, or quote the buffered date and be reliable. Reliability wins repeat business, and the buffer is idle time in the schedule, not idle time on any machine, so it costs no capacity.
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