Should the line halve its batch size?
Earlier small batches can consume the shift in setup work.
“You produce the required amount, you stop, you change over” (opens the source)
The question
Rill Works has one 480-minute shift. Eight products each need 40 units. Processing takes one minute per unit. Each run, including the first, requires a setup. Partial shipments are allowed.
| Runs | Units per run | Setup minutes | |
|---|---|---|---|
| Large batches | 8 | 40 | 20 |
| Small batches | 16 | 20 | 20 |
Run time and setup time use the same line; they cannot overlap.
“Which plan meets all 320 units? What changes if setup takes five minutes?”
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A strong answer, step by step
Open each step in turn. This is one strong answer, not the only one.
Step 1: Count every setup
What would you do here? Open the move you’d make.
Omit the first setup.
Tempting, but it misses something. The packet requires a setup before the first run too.
Count a setup before each run.
The strong move. The first setup consumes time too.
See how a strong candidate says it
“Eight large runs need 160 setup minutes plus 320 processing minutes: 480 total.”
Why it works: The first setup consumes time too.
Step 2: Check the whole small-batch plan
What would you do here? Open the move you’d make.
Compare total required time with the shift.
The strong move. An earlier first batch does not guarantee the full order fits.
Choose small batches because the first is sooner.
Tempting, but it misses something. A faster first batch can accompany a much later final batch.
See how a strong candidate says it
“Sixteen small runs need 320 setup minutes plus 320 processing minutes: 640 total.”
Why it works: An earlier first batch does not guarantee the full order fits.
Step 3: Count output at the cutoff
What would you do here? Open the move you’d make.
Claim all 320 units arrive over the shift.
Tempting, but it misses something. Sixteen 40-minute runs require 640 minutes, beyond the shift.
Count what is finished at minute 480.
The strong move. Each completed small run takes 40 minutes.
See how a strong candidate says it
“At 20-minute setups, twelve small runs fit: 240 units. Eighty units remain unmade.”
Why it works: Each completed small run takes 40 minutes.
Step 4: Remove setup loss first
What would you do here? Open the move you’d make.
Test the smaller batch after reducing setup.
The strong move. Setup reduction makes smaller batches feasible.
Reduce batch size without changing setup.
Tempting, but it misses something. Sixteen long setups still consume 320 minutes of the shift.
See how a strong candidate says it
“At five-minute setups, sixteen small runs finish in 400 minutes. The first batch finishes at minute 25.”
Why it works: Setup reduction makes smaller batches feasible.
The answer, in short
- Decision
- Keep the large batches until setup loss is reduced.
- Because
- They meet the shift plan; the initial small-batch plan does not.
- What would change it
- Five-minute setups let all small batches finish with 80 minutes spare.
Only ten minutes can be saved per setup. Does the small-batch plan now fit?
Common traps
- Ignoring the first setup.
- Equating early partial output with a complete shift plan.
Check your answer
- I counted runs and setups.
- I separated setup and processing.
- I checked output by shift end.
- I tested setup reduction.
Last reviewed Nov 10, 2026