The Big Question—What is 3D Printing? - 3D Printing: Build your Own 3D Printer and Print your own 3D Objects - page 17

along the X axis. Likewise, when the hot-end moves forward or backward (again,
when viewed from the front), the hot-end is moving along the Y axis.
Now go back to Figure 1.9 , which shows the 3D printer from the front. Can you
see the Z axis now? When the hot-end moves up or down, it's moving along the Z
axis.
Here's another idea to mull over. If you look at the 3D printer from above, imagine
that the X axis can be used to define a two-dimensional object's length (like a
square). The Y axis can be used to define that two-dimensional object's width. So
what do you think the Z axis will be used to define for an object? If you answered
“height,” you'd be correct.
A 3D printer's motors will be used to move the hot-end left, right, back, forward,
up, and down. While these movements are occurring, the extruder is constantly
pushing in the filament to melt in the hot-end and then coming out the hot-end's
nozzle a thin thread of melted plastic. This melted plastic continues to extrude at a
constant rate, almost like ink from a pen as you write your name on a piece of pa-
per. The only difference is that as the plastic cools, it begins to harden. Any melted
ink placed on top of an existing (hardened) bit of plastic will simply add to the
height of the plastic at that point. And that's how we get the layering effect that a
3D printer uses to print 3D objects!
Let's return to that solid black square drawn on a piece of paper. If we use our 3D
printer to create that square, what will be required? The extruder needs to move
along a path that lets the melted plastic form a square that has the same thickness.
Two possible paths it could follow are shown in Figure 1.11 .