Paste the bottleneck machine’s jobs and see in seconds which order is least late, which spends least on setups and when each job is done. Print the shift order with a check column.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Click a row to see the Gantt chart and dispatch list for that rule. ✓ marks the best value in each column.
Priority rules and Johnson’s rule give a good sequence that is easy to explain on the shop floor, but not necessarily the optimum for every criterion at once (Johnson’s rule is optimal only for the two-stage makespan).
Makespan, total tardiness and total setup for each rule, in the same hours.
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It is choosing the order in which jobs go through a machine or a line. The order changes time spent on setups, when each job is finished and how many are late. This calculator tests six simple rules at once and shows the Gantt chart and dispatch list for the one picked.
Processing time = job quantity × standard time per part (from a time study or routing) ÷ actual efficiency. Full setup is the measured changeover from one family to another; the short setup is the adjustment between jobs of the same family (only changing color or length, for example). Use measured times, not the machine manual’s.
With the five example jobs and a 0.25-hour short setup within a family, the order entered (FIFO) finishes at 32.50 h with 26.00 h of tardiness in three jobs. EDD (earliest due date first) finishes at 31.25 h with 6.00 h of tardiness in two jobs; grouping families finishes at 29.50 h with 3 h less setup, but delays the urgent jobs more.
If customers press on dates, use the least total tardiness or EDD, which usually gives the smallest maximum delay. If the machine is the bottleneck and setups are long, the family rule gains production hours. SPT cuts average queue time and work in process. The criterion on the form picks automatically; click the table to see another rule.
For two stages in series with the same order at both (e.g. machining then heat treating), Johnson (1954) proved this order gives the minimum makespan: first the jobs faster at stage 1, in increasing order; then the jobs faster at stage 2, in decreasing order of stage 2. In the example the makespan drops from 34 h to 30 h.
Not necessarily. Priority rules give a good sequence that is quick to compute and easy to explain, but with sequence-dependent setups the problem is hard and the exact optimum needs mathematical programming. For dozens of jobs at a bottleneck, the best rule on this page is usually close to the optimum; always check with the people who know the machine.
It assumes all jobs are released at the start, one machine (or two in series), no breakdowns, no material shortages and no splitting a job. The calendar is hours per day from the start time, without weekends or holidays. For several parallel machines or different routings, use a scheduling (APS) system or split the load first with the capacity calculator.
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