Students halve the layer height and see the time double, compare infill and walls on time and strength, see Sam's 100% infill take three hours, slice a real part one setting at a time, sort parts by the setting that matters, and meet a strength-and-time brief.
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Students will be able to
I can predict how layer height, infill and walls change a print.
I can choose settings for what a part needs.
Timing
Predict and Try 6 min · Worked example 8 min · Real slicer 12 min · Practise and Make 10 min
Before class
The board is a simple model of a 40 × 40 × 20 mm block (PLA, 1.24 g/cm³): time grows with plastic and with 1 ÷ layer height; strength grows mostly with walls. Real numbers depend on the printer, speed and part shape; the slicer step replaces them with yours. Printer time is the bottleneck: set a maximum print time per student.
Running the lesson
Predict: ask why thinner layers would take longer.
Worked example: let students test each option on the board first.
The hard part (on purpose)
Students max every setting. Keep asking what the part needs, and what each setting costs.
When students get stuck
What you will see
A question to ask
The fix
A student's settings take hours.
Which setting is buying strength, and which is just adding plastic?
More walls, less infill.
Answers to the checks
thinner layers: A part takes 80 minutes at 0.2 mm layers. At 0.1 mm layers it takes about… About 160 minutes: twice as many layers, each taking about as long.
Layers: Halve the layer height (0.1 mm). What happens to the time?
81 to 163 minutes: doubled.
Infill: Put the layer height back to 0.2 and set infill to 100%. Compare the time and the strength with 20%.
Time and plastic more than double (81 to 192 minutes); strength rises from 51 to 79.
Walls or infill?: From 2 walls and 20% infill, which change adds the most strength for the least extra time? Add two walls (4 walls, 20% infill) On the board: 4 walls gives strength 95 in about 106 minutes; 60% infill gives only 65 in about 137.
Find the mistake: Sam's print takes three hours and isn't much stronger. Click the line where Sam's reasoning first goes wrong. line 2 Line 2: most of a part's strength is in its walls. Past about 20–30%, infill costs lots of time and plastic for little strength; add walls instead.
trade-offs: Which setting matters most for each part? A display model to look at → Thinner layers (finish); A bracket that holds weight → More walls (strength); A quick test print to check a fit → Low infill (speed and plastic); A figurine with fine detail → Thinner layers (finish); A hook for a heavy bag → More walls (strength) Choose the setting that buys what the part needs; everything else stays at the defaults.
strong and quick: The bracket needs strength 80 or more, and the queue allows 100 minutes at most. Find settings that do both.
More walls and little infill: strength from the walls, time saved inside.
Solutions
One possible solution for each task. Other correct programs are fine.
strong and quick
Open task: any program that does what the step asks.
Stretch and support
Stretch: Infill patterns (grid, gyroid): find out what each is good for.
Support: A three-row table: setting, what it buys, what it costs.
Exit ticket
Your part must be strong and printed quickly. Which two settings do you change, and how?
More walls and lower infill (keep normal layer height).
What each step is for
thinner layers: Committing to the effect of halving layer height tests the new move: time scales with the number of layers.
Try: the settings: Changing one setting at a time on the board settles the prediction and shows infill's poor value.
Worked example: what buys strength: Comparing walls and infill on time and strength models the move; Sam's 100% infill is planted after the method.
Slice it for real: The school's slicer gives the real time and grams for the same changes, so students calibrate the board's model.
trade-offs: Choosing settings for different purposes.
strong and quick: Meeting two criteria at once (strength and time) forces the trade-off decision.
Where it leads
Next: Parametric design (Years 9–10), or a Capstone project's enclosure.