Job Shop Scheduling

Why job shop scheduling is hard

Unlike process manufacturing (where you make the same thing every day), job shops make different parts with different routings on shared equipment. Job A needs the lathe for 3 hours, then the mill for 2 hours. Job B needs the mill for 4 hours, then grinding for 1 hour. They share the mill. Who goes first?

Multiply this by 20 concurrent jobs and 8 machines, add in rush orders, material delays, and an operator calling in sick, and you understand why scheduling is where most shops lose money they never see — in idle time, late deliveries, and overtime that shouldn't have been necessary.

Scheduling approaches

Forward scheduling starts from today and schedules forward: "If I start this job now, when will it finish?" Backward scheduling starts from the due date and works backward: "To deliver by Friday, when does each operation need to start?" Most job shops use forward scheduling for the floor and backward scheduling for delivery promises.

Finite capacity scheduling respects that a machine can only run one job at a time. Infinite capacity scheduling assumes unlimited resources and just flags overloads. For a real shop floor, finite capacity is the only honest approach — but it requires knowing your actual capacity, which means tracking your machines, their shifts, and their utilization.

What to look for in scheduling software

A visual scheduling board that shows jobs on a timeline by resource is the minimum. You should be able to see at a glance: (1) what's running on each machine, (2) when current jobs finish, (3) where the conflicts are, and (4) how much capacity you have this week and next week.

Bonus: drag-and-drop rescheduling, automatic conflict detection, and integration with your job and quoting data so due dates and operation times are already populated.