Students turn an L-bracket through four print orientations, find the one that needs supports and the one with layers along the load, apply both questions to a hook and other shapes, see Sam's bracket snap across its layers, check orientations in the school's slicer, and justify an orientation for a part of their own.
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Students will be able to
I can tell when a part needs supports.
I can choose a print orientation so the load runs along the layers.
Timing
Predict and Try 6 min · Worked example 8 min · Slicer 10 min · Practise and Make 10 min
Before class
The 45° rule is a rule of thumb; bridges (short spans between two supports) print without supports too. The board's four orientations are drawn for one bracket; the slicer shows the real supports and time.
Running the lesson
Predict: have two printed bars ready to snap after the reveal.
Slicer: show layer preview colouring.
The hard part (on purpose)
Layer direction is invisible on screen. Snap two printed test bars (one printed flat, one upright) in front of the class.
When students get stuck
What you will see
A question to ask
The fix
A student chooses the way that looks most like the finished object.
Which way does the load pull, and which way do the layers run?
Turn it so they run the same way.
Answers to the checks
strongest way: An L-shaped bracket will hold up a shelf. Which way should it be printed to be strongest? Flat on its side: no supports, and every layer runs along both arms, so the load pulls along the layers, not across them.
Supports: Turn the bracket round until it needs supports.
Upside down: the foot sticks out over nothing.
Strongest: Find the way that needs no supports and puts the layers along the load.
Flat on its side.
Overhang, then load: A hook will hang a bag from its curved end. The load pulls down the hook's length. Which way up should it be printed? Flat, so the layers run along the hook Flat: no tall overhangs, and the layers run along the load.
Find the mistake: Sam's bracket snaps across the arm the first day. Click the line where Sam's reasoning first goes wrong. line 3 Line 3: a printed part is weakest across its layers. Foot down, the shelf load bends the arm across them.
which way?: Which of these need supports printed as described? A letter T standing up, its bar at the top → Needs supports; A letter T lying flat → No supports; A pyramid standing on its base → No supports; A pyramid standing on its point → Needs supports; A cube with a round hole straight through, top to bottom → No supports Anything that sticks out sideways over nothing (the T's bar, an upside-down pyramid) needs supports; sloping in at 45° or less doesn't.
A phone stand: A phone stand is a flat back plate with a ledge sticking out at the bottom. It will be printed lying on its back. What happens to the ledge? It points up from the bed: no supports, and the layers run along the plate On its back, every feature grows straight up from the plate.
Stretch and support
Stretch: Why do some parts get split into two pieces for printing and glued?
Support: A card with the two questions: what overhangs? which way does the load pull?
Exit ticket
Give two reasons to choose a print orientation.
To avoid overhangs that need supports, and so the load runs along the layers rather than across them.
What each step is for
strongest way: Committing to the strongest orientation before seeing layers tests the 'equally strong every way' picture.
Try: turn it round: Turning the bracket through all four ways settles the prediction: supports in one, weak layers in three.
Worked example: two questions for every part: Asking 'what overhangs?' and 'which way does the load pull?' of every part models the move. Sam's 'equally strong every way' is planted after the method.
Make it in the slicer: In the school's slicer, supports and layer direction are visible before printing: the habit to build.
which way?: Applying both questions to new parts.
choose and justify: Choosing an orientation for a new part and giving both reasons is the design decision students will make on every print.