Is 3D printing really just 2D printing? Because only 2 motors move per layer
I was wondering the other day why don't all three motors move at the same time?

That is perfectly possible for most printers (with limitations, &quot;3D Printing&quot; with all steppers being used is called &quot;non-planar&quot; printing), but there are some major cons you need to deal with. First, there are not that many software suites that slice objects perfectly well like the &quot;normal&quot; per &quot;fixed/variable layer height&quot; slicing as the slicers are under developed. Second, it requires a specific tall and slender nozzle/print head, else the height of printing is very limited. Last, besides generally not being useful for rectangular prints (except for 90° overhanging structures1)), this method is only/best suitable for curved objects as the top layer will follow the contours of the object.

It makes sense if a 3D printer really does print with all three motors moving.

No, it does not make sense, the essentials of 3D printing it that it produces a 3D object, not that all stepper motors should be running simultaneously.

Won't it also be more efficient if they do 3D print in all axes?

Not necessarily, there are limitations to non-planar printing like geometry and print quality, but, you could (in some cases) print with less support material.

1) : From Rene K. Mueller, published March 3, 2021, https://xyzdims.com:


Note that these are demonstration pieces, normally you would rotate the print for 90° and print it sliced normal (planar).