Plain talk, with jokes

Lights-out manufacturing: what actually happens at 2 AM

October 1, 2026 · 3 min read

The brochure shows a dark plant humming along while the owner sleeps. The reality is a text message at 2:14 AM that says FAULT 118 and a decision about whether to drive in. Here is what unattended production looks like after the ribbon is cut, and how to design the night so the phone stays quiet.

The short answer

A tending cell that runs unattended is buying you machine hours while nobody is there, and those hours are real money. But the robot is the easiest part of the night. The hard parts are everything a person quietly handled without being asked: clearing chips, topping off coolant, noticing the tool that started to chatter, swapping the pallet, and deciding what to do when something stops. Plan those and the phone stays dark. Skip them and you have bought a very expensive alarm clock.

The first night, honestly

The arm loads the first blank at 6:10 PM. The cycle runs. At 9:40 the chip conveyor backs up because nobody planned for the extra volume, and the machine alarms. The robot, obedient as Asimov's second law, waits politely for an instruction that never comes. At 2:14 AM the owner, who set up a text alert because the integrator suggested it, wakes to FAULT 118 and lies there doing arithmetic about whether four more hours of cutting is worth a 25 minute drive. This is a true story in the sense that it is every shop's story. The details change. The 2 AM does not.

What has to be designed, in the order it will bite you

Chips. A machine that runs eight hours attended and twelve unattended produces far more swarf than its conveyor was sized for. Plan the conveyor, the bin and the frequency before the robot.

Coolant and tooling. Concentration drifts, tools wear, and a person compensates without noticing they are doing it. Unattended, you need a tool life count that stops the cell before the insert fails, and a coolant plan that makes it to morning.

Part presentation. A table of blanks on a grid, a drawer system, or a pallet pool decides how many hours one load buys. Fifteen blanks at 40 minutes each is ten hours. Fifteen blanks at 4 minutes each is one hour and a very short night.

Alarms with a decision tree. Every alarm should map to one of three actions: the cell recovers itself, the cell stops safely and waits for morning, or a person gets called. If every alarm calls a person, nobody will do the job for long.

The recovery plan. When something stops at midnight, is the part scrap or salvageable? Does the program restart from the top or from the interrupted operation? Who checks the first part in the morning? These are written down by the shops that make lights-out work, and improvised by the ones that quietly go back to one shift.

Who owns the phone?

Somebody has to, and it should be decided before the purchase order. In most small shops it is the owner for the first month and then, if the cell is designed well, nobody, because it stops being interesting. If it is still the owner in month four, the problem is not the owner. It is the chip conveyor.

The number that makes it worth it

Spindle hours you can sell. The published account on this site of a Washington shop that filled its night shift with one cobot reports weekly output rising from 255 to 370 parts, as the vendor and trade press published it, on a 56 minute cycle where the robot works six minutes. That is what a well designed night looks like: the robot is barely busy, the machine is cutting the whole time, and the owner is asleep.

If you want to know how many unattended hours your machine and your parts would actually buy, describe them to Joe, the concierge here. He will ask about the door, the chips and the table before he says a word about arms, which is the right order.

Related on this site

• CNC machine tending
• What changed when a Washington machine shop filled its night shift with a cobot
• Who will run the cell
• The last ten percent
• Robots for machine shops