Level 1Unit E · Session 30
30

Unit E · Designing a real thing

From the screen to your hand

What we are making: nothing new. Today your part comes back as an object, and you find out how close the machine got.

How it actually got made

Hot endmelts the plastic, ~200°CBedholds the print downFilament1 kg of plastic on a reelYour partgrown from the bed upFour things to know. That is genuinely all.The hot end reaches 200°C and does not look hot. Never reach into a running printer.
Four things. The hot end is the one that can hurt you.

The printer cannot make a solid shape in one go. It draws one flat outline in melted plastic, moves up a fraction of a millimetre, and draws the next one on top.

What you drewWhat the slicer made of it16 layers0.2 mm eachThe printer cannot make a solid shape. It can only put down one thin line of melted plastic at a time,then move up 0.2 mm and do it again. A 20 mm tall object is a hundred layers.
A 20 mm tall part is about a hundred layers.
💡 Tip
You can see the layers on your part if you look at the side. Run a fingernail across it — those ridges are the individual passes. That is what 0.2 mm feels like.

Do it — measure what you got

This is the real work of the session, and it is the same skill as calibrating a sensor.

  1. Take your part. Find the drawing in your notebook with the numbers on it.
  2. Measure the printed part with a ruler. Same three measurements.
  3. Write both sets down, side by side: what I drew, and what I got.
  4. Work out the difference for each one.
  5. Now try the fit. Does your sensor go in? Easily, tightly, or not at all?
What I drewWidth 40.0 mmDepth 20.0 mmSlot 16.5 mmThese are the numbersyou typed in.What I gotWidth 40.2 mmDepth 20.1 mmSlot 16.1 mmClose, but never exact.The slot shrank most.
Fill this in for your own part. The differences are small and they are not random.

The lesson

The machine is not broken. Every machine that makes real things is a bit off, and the job of the person using it is to know how much, and in which direction, and to allow for it.

You did exactly this in Session 14 with the light sensor. You did not trust the number until you had checked it against something real. This is the same habit, applied to a machine instead of a sensor.

💡 Tip
If your part does not fit, that is not a failure — it is a measurement. Change the number by the amount you were out, and it will fit next time.

Try it

  1. Fix your design using the differences you measured. Do not guess — use your numbers.
  2. Compare parts with another team. Did theirs shrink the same way?
  3. Fit your part to your project. It is going on the exhibition table.

End of Unit E

  • You can build a shape out of simpler shapes, in millimetres.
  • You can measure a real thing and design a part around it.
  • You know that holes must be drawn bigger than what goes in them.
  • You know a printed part is never exactly the size you drew.
  • And you measured the difference yourself.
Challenge optional — only if you finish early
  • Measure the same part five times. Do you get the same number every time?
29. Design something that fits