Slicer trade-offs

The slicer's settings trade time and plastic for finish and strength. Halving the layer height doubles the time. Infill past about 20–30% costs a lot for little strength; extra walls add more strength for less.

The printer queue is a week long and your part takes four hours. Which settings can you change without making it worse, and which actually matter?

The slicer turns a 3D model into layers and a path for the nozzle. The three settings that matter most:

Layer height: thinner layers give a smoother finish, but there are more of them.
Infill: how full the inside is (0% hollow, 100% solid).
Walls (perimeters): how many lines thick the outside is.

Predict: Read the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
Try: Try it on the board and compare the result with your prediction.
Investigate: Work out why it happens, one step at a time.
Modify: Change the problem on purpose and see what happens.
Practise: A few on your own, to check you have it.
Make: Make your own problem using what you have learned. Expect a few tries; that is normal.

WidthMore contexts, same idea.

PredictRead the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.

Thinner layers

A part takes 80 minutes at 0.2 mm layers. At 0.1 mm layers it takes about…160 minutes40 minutes90 minutes80 minutes

TryTry it on the board and compare the result with your prediction.

Try: the settings

Try it yourselfYour edits are saved in this browser.

Halve the layer height (0.1 mm). What happens to the time?

Use the board. This ticks when you get there.

Put the layer height back to 0.2 and set infill to 100%. Compare the time and the strength with 20%.

Use the board. This ticks when you get there.

InvestigateWork out why it happens, one step at a time.

Worked example: what buys strength

Worked exampleBefore each step, say what you think comes next.

$\text{layers } 0.2 \to 0.1$ Twice the layers: twice the time. Buys finish, not strength.
$\text{infill } 20\% \to 100\%$ More than twice the time and plastic; strength rises a little.
$\text{walls } 2 \to 4$ A little more time; strength rises a lot.
$\text{strong and quick}$ More walls, modest infill, normal layers.

Now pick the best buy.

From 2 walls and 20% infill, which change adds the most strength for the least extra time?Halve the layer heightAdd two walls (4 walls, 20% infill)Raise infill to 100%Raise infill to 60%

Sam's print takes three hours and isn't much stronger. Click the line where Sam's reasoning first goes wrong.

Modify TypicalChange the problem on purpose and see what happens.

Slice it for real

In our slicer, I sliced my part at 0.2 mm / 20% / 2 walls, then changed one setting at a time, and wrote down the real time and grams for each.

PractiseA few on your own, to check you have it.

Trade-offs

Which setting matters most for each part?

A display model to look at

A bracket that holds weight

A quick test print to check a fit

A figurine with fine detail

A hook for a heavy bag

MakeMake your own problem using what you have learned. Expect a few tries; that is normal.

Strong and quick

Try it yourselfYour edits are saved in this browser.

Need a hint?

Infill costs time; walls buy strength.

Another hint

Try lowering the infill and adding walls.

Another hint

4 walls and 0–10% infill at 0.2 mm layers.

The bracket needs strength 80 or more, and the queue allows 100 minutes at most. Find settings that do both.

Use the board. This ticks when you get there.

For teachers

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. About 40 minutes.

Open the teacher guide: answers, solutions, slides and a worksheet.

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.

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

A student's settings take hours. Ask: Which setting is buying strength, and which is just adding plastic? Fix: More walls, less infill.

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.

Where it leads

Next: Parametric design (Years 9–10), or a Capstone project's enclosure.

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.

Now you can

Predict how layer height, infill and walls change a print.
Choose settings for what a part needs.

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Source: content/engineering/cad/slicer/lesson.md