Waiting

Waiting is the largest waste hiding in most small shops and the one teams notice last, because nothing is visibly wrong while it is happening. A part sitting in a queue is just a part sitting in a queue. It is not on fire, no alarm is sounding, no one is yelling about it. The lean view is that every minute that part is not advancing toward the customer is a minute the shop is paying for and not getting paid for.

"If the part is not moving forward, the bill is moving forward without it."

How waiting works as a waste

Waiting is idle time when work, people, or material are not moving, and one of the eight wastes of lean manufacturing. The category covers several specific patterns:

• Queue time between operations: parts sitting in totes or on carts between two workstations. This is usually the biggest single bucket.
• Operator idle time during machine cycles: an operator standing at a machine running an unattended cycle with no other work to do.
• Material waiting for tools or fixtures: a part ready to run held up because the right fixture is in use elsewhere.
• Inspection wait: a finished batch sitting awaiting a QC sign-off, often because inspection is centralized rather than at the workstation.
• Information wait: an order stalled because a drawing, a customer release, or a routing decision has not arrived.
• Setup wait: a job waiting for the upstream operation to finish a changeover before it can start.

The standard diagnostic is value stream walking with a stopwatch. Pick a part and time every step from order receipt to ship. Total the value-added time (the minutes the part is being changed by a worker or machine) and the elapsed time (the wall clock from order to ship). The gap is mostly waiting. Most small shops find a ratio of 5 to 15 percent value-added time, meaning 85 to 95 percent of elapsed time is some form of waiting.

The countermeasures fall into three categories:

• Reduce batch sizes so queues are shorter. This usually requires cutting setup time first, often with single-minute exchange of die.
• Balance the line so no operation runs significantly slower than the others. Slow stations create persistent queues.
• Install pull signals so parts only move when downstream needs them, preventing accumulation in queues.

Most of these countermeasures are about flow design, not about pace. Operators working faster does not remove waiting. Layout and signal design do.

Where waiting fits on the shop floor

In a 25-person machine shop running parts for two industrial customers, waiting shows up in a pattern most owners recognize. Saw cuts feed the mill in oversized batches because setup at the mill takes 90 minutes. Milled parts queue at the mill for an average of 36 hours before the next batch is started. The next operation, a Lathe Cell, only sees parts twice a day when batches transfer. Between transfers, the lathe operator is idle for 90 minutes at a time waiting for material, and during transfers the lathe runs at full pace while parts queue at deburr downstream.

Total elapsed time from saw to shipping bench: 72 hours. Total value-added time touching the part: about 20 minutes. The ratio is 0.5 percent. A first improvement pass targets the mill setup with SMED, aiming for 30 minutes per changeover. Smaller batches follow, mill queues drop from 36 hours to 8 hours, lathe idle time drops because material flows more steadily, and elapsed time drops from 72 hours to 28 hours over three months. None of the equipment changed and nobody worked faster.

Common mistakes with waiting

• Confusing waiting with downtime. Downtime is equipment-specific. Waiting is the broader category. They have overlapping but different fixes.
• Solving waiting by speeding up operators. Operators are not the constraint; the layout and the batch size usually are.
• Adding inventory to mask waiting. Buffering between operations hides the waiting but does not remove it, and it adds excess inventory waste in exchange.
• Centralizing inspection. A central QC bench creates predictable waiting queues. Decentralized inspection at the workstation usually wins.
• Skipping the stopwatch walk. Waiting is invisible until somebody times it. The walk is the first concrete step.

Waiting and related Lean tools

Waiting is one of the canonical 8 wastes, tightly linked to excess inventory, since material waiting in a queue is also material held in stock. The metric that captures the full cost of waiting in a value stream is lead time, the elapsed time from order to ship. The most common cause of waiting is equipment-specific downtime, which makes downtime tracking a useful starting point for finding the biggest queues.