STL isn't a smooth curved surface - it's actually a collection of triangles. The more triangles you have, the smoother the curved surface is.

For a 1:10th scale model of the car I want to make, it's 20716 triangles - the full size is 82,864 (as it currently stands - I still haven't finalised the design).

I wrote my own software for converting the STL file into G-code, suitable for my machine (2.5D). It also splits the object up into the blocks we'll be using, and gives me an estimate of the number of blocks required (63 at the moment).

The only caveat is that it only works to the nearest 1mm, which is fine for my requirements. It could be written to go much finer than that.

I've also got a number of different algorithms which trade off accuracy against speed.

Oh, and it's MacOS only as well (could be important for some, well most people!)

This is why machine is called "STLCutter"