A printer builds in layers: an overhang more than about 45° from vertical needs supports, and a part is weakest across its layer lines. Choose the way up that needs no supports and runs the layers along the load.
Two brackets, same file, same printer, same plastic. One holds a shelf of books; the other snaps the first day. The only difference is which way up they were printed.
Each layer sits on the one below. A wall leaning more than about 45° from vertical has nothing underneath, so the slicer adds supports (extra plastic you break off later). And layers stick to each other less well than plastic sticks to itself along a layer, so a printed part is weakest across its layer lines.
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.
Make your prediction first. Help opens once you've locked it in.
PredictRead the problem and decide what you think before you try anything. A wrong guess is fine: it shows you what to look for.
Strongest way
TryTry it on the board and compare the result with your prediction.
Try: turn it round
Try it yourselfYour edits are saved in this browser.
Turn the bracket round until it needs supports.
Use the board. This ticks when you get there.
Find the way that needs no supports and puts the layers along the load.
Use the board. This ticks when you get there.
InvestigateWork out why it happens, one step at a time.
Worked example: two questions for every part
Worked exampleBefore each step, say what you think comes next.
overhang>45∘⇒supportsEach layer needs something under it.
layers across the load⇒weakLayers bond less well to each other.
bracket: flat on its sideNo overhangs, and the layers run along both arms.
check both, every partSupports cost plastic and finish; weak layers cost the part.
Now try a hook.
Sam's bracket snaps across the arm the first day. Click the line where Sam's reasoning first goes wrong.
Modify TypicalChange the problem on purpose and see what happens.
Make it in the slicer
PractiseA few on your own, to check you have it.
Which way?
Which of these need supports printed as described?
A letter T standing up, its bar at the top
A letter T lying flat
A pyramid standing on its base
A pyramid standing on its point
A cube with a round hole straight through, top to bottom
MakeMake your own problem using what you have learned. Expect a few tries; that is normal.
Choose and justify
For teachers
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. About 40 minutes.
I can choose a print orientation so the load runs along the layers.
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
A student chooses the way that looks most like the finished object. Ask: Which way does the load pull, and which way do the layers run? Fix: Turn it so they run the same way.
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?
Where it leads
Next: Slicer trade-offs.
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.
Now you can
Tell when a part needs supports.
Choose a print orientation so the load runs along the layers.