Stop the moment something is wrong. The run costs more later.
Stop the line is the active behavior that makes a lean quality system work. It is also the practice most often present on the wall as a poster and absent in actual production. The reason is simple: stopping the line costs visible production time, while the defect-passed-downstream costs invisible rework and returns. The shop that learns to stop is the one that has done the math and concluded that the visible cost is smaller than the invisible one. Most shops have never done that math.
"The hour you don't run today is cheaper than the customer return you ship next week."
Stop the line is built on three things, in this order.
Some way for the operator to trigger a stop and call for help. In Toyota plants this is the andon cord. In a small shop it can be a light tower, a button, a phone call, or just a raised hand. The mechanism is not the hard part. Any visible, fast signal works.
A team lead or supervisor responds within a defined window, usually under a minute. They arrive, look at the problem, and decide one of three things: clear it in place and release the line, pause briefly for a fix, or call a longer huddle to find the cause. The response is fast because if it is not, operators stop using the mechanism.
When the stop happens for a non-trivial reason, the team finds the cause before resuming. The discipline is usually a brief five-whys conversation at the spot where the problem appeared. The line restarts after the cause is identified, not after the immediate symptom is cleared. Without this discipline, stop-the-line becomes "stop and clear the jam," which guarantees the next jam.
The whole sequence usually takes between 30 seconds and 15 minutes, depending on the issue. Most stops are short. The few that turn into longer investigations are the ones that produce the biggest reductions in defect rate over the following weeks.
Picture a 30-person plastics injection molding shop running closures for a beverage brand. The shop has three presses and a leadership team that prides itself on keeping the presses running through everything. Operators have been trained, informally, to keep producing and tag bad parts for later review. Returns from the customer for cosmetic defects are running about 2 percent of shipments.
A stop-the-line rollout would not require new equipment. It would change the standing rule. Any molder who pulls a part and sees a defect immediately calls the shift lead and idles the press. The shift lead arrives within a minute. If the defect is a one-off, they release the press and the molder restarts. If the lead sees the defect has been there for more than a few shots, the press stays down and they huddle to find the cause. The first week, presses are down more than usual. Production drops by maybe 8 percent. By week four, the recurring causes have been fixed and presses are down less than before the change. The cosmetic return rate falls under 0.5 percent within two months.
Stop-the-line is the action; line stop authority is the standing right of any worker to take it. The most common signaling mechanism is an andon cord or button, which triggers help to arrive at the station. On moving assembly lines, the action is often constrained by a fixed position stop system, which lets the line continue briefly to a defined breakpoint before halting. Together, these tools express the broader jidoka pillar: stop, find the cause, fix it, and never let the same problem make a second defect.
The questions we hear most about this term.
Long-form guides that pick up where this definition leaves off, written for manufacturers running Arda today.
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