Eli5: How do CNC machines convert digital images into real objects through mechanical movement?

Question

So an electric motor converts electricity into mechanical movement.. But how is Code and digital data converted into mechanical movement ?

In: 2

Answer 1

In very general terms:

You give CNC machine the digital description of a shape. This describes the geometry of the surface in very strict terms. If you had the skill to memorize and visualize the coordinates of 15 million points in Euclidean space, you would be able to also imagine, draw, or carve roughly the same shape from just looking at a list of 35 million numbers.

Once the CNC machine has this shape as a description, you set up your raw material on the machine’s working surface very specifically (it has a “center point” or a “zero point” where counting of dimensions starts from).

Then you set up the machine with the settings of the carving bit it uses. Different bits have different dimensions, and the machine needs to account for that.

From there on, it’s just a matter of the machine moving its carving bit into very specific locations and along very specific paths that trace the surface of the shape with the edge of the carving volume of a the bit.

Overall, you can try the following exercise at home:

1) Get a spherical lollipop, like a chupa-chups. This will be your carving bit.

2) Get a complex shape you’ll want to replicate.

3) Put that shape on a tabletop, then hold your lollipop by the stick and put the round thing on the shape. Start tracing that shape in parallel lines from one end to another. You can see that the lollipop never enters inside the solid matter of the shape, only tracing its curvature. This is exactly what a CNC machine does, but:

* instead of the shape you have the literal description of the shape
* instead of the lollipop you have deadly-sharp carving bit that takes off any material it enters
* instead of the empty space around the shape, you have solid raw material of your choice (wood, plastic, metal)

And the CNC machine, from that 35 million numbers, calculates how much to move the bit so that it does not enter inside the solid matter of the shape but just barely touch the surface.