3D Printing: Model vs Real World

When you design something inside the computer, you have complete freedom over the size.

  • There’s nothing to stop you from designing something tiny or HUGE.
  • There’s nothing to stop you from setting dimensions to impractically precise values like 10.0003 mm.

Can you make absolutely any design real? With hand tools, 3D printers or other manufacturing techniques?

No. (Sorry)

Have an Impractically Tiny Violin.

In Introduction to 3D Printing we talked about the general limitations of 3D printing.

  • There’s a limit to how small we can print. (because of the nozzle size – and some other physical limits)
  • There’s a limit to how HUGE we can print. (because of the printer size, and how long it takes)

How accurate is a 3D printer?


If you design a cube that is 30 mm on each side,
And you 3D print it,
Will it be exactly 30 mm in real life?

No. (Sorry again. Wow, this article is just full of disappointment…)

Okay fine. How close is it?


In Fusion 360 you learned that there is actually a use for mathematics and geometry. (tangent and coincident and parallel, oh my!)
Now it’s time for a SCIENCE experiment! (no explosions this time, sorry again)

We designed some small models in Fusion 360.
As you can see below;

  • They are squares each nominally 30 mm wide.
  • Inside is a smaller square of varying size,
  • There is some text on it, with the smaller square’s dimension.
  • The objects created are all nominally 8 mm high.


Next is a Section view,

  • Two objects are visible.
  • One has a square peg, the other has a square hole.
  • We also set Display Settings () > Visual Style to ‘Wireframe with Hidden Edges’ so that the internal structure is visible.
  • There is a clear gap between the peg and the edges of the hole.


Next we 3D print them – so we can measure them and see how printed objects compare to models.

MINI PITSTOP|TOP TIPS: Crayons! Rub on, scrape off, lovely colours.

Class Questions:

Take measurements as a group, and write down the answers to each question.

  1. What is the outside length, width and height of the objects?
    • Is it exactly 30 mm x 30 mm x 8mm?
    • Are the objects all the same?
  2. How do the peg sizes compare to the nominal dimension printed on the back?
    • Do you observe a consistent error between nominal and actual dimensions?
    • Why does the peg design have a fillet on the corners?
  3. How do the hole sizes compare to the nominal dimension printed on the back?
    • Do you observe a consistent error between nominal and actual dimensions?
  4. How much larger than the peg piece does the nominal size of the hole piece need to be?
    • For the piece to fit snugly?
    • For the piece to fit smoothly?
    • For the piece to fit loosely?


What did you learn in this exercise?

  1. How should your designs in Fusion 360 allow for the inaccuracy of 3D printing?
    Are there any general rules you can think of?
  2. If you have the dimensions of a real component, (for example an LED ring)
    and need to have it fit inside a Fusion 360 design, (for example what we’re doing next)
    how much of a gap should there be?

Lastly – don’t think that you can’t make fine details or awesome things with a 3D printer!
Here’s something designed in Fusion 360 and printed on a cheap $300 printer.
It’s tiny!

aaand here’s a life sized 3D printed elephant.


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