When machining 3d models in raster mode and zero angle, the toolpath starts machining from the "bottom" of the model, proceeds up an inch or two and then, at times, skips to a different part of the model and begins machining there. Eventually, all the model is machined, but I have noticed lines in the material...sometimes small ridges and other times small valleys where the two toolpaths meet. I asked our Vectric friends and they told me that is normal behavior when the 3d model has irregular shapes. My guess is that the algorithm is minimizing machining time. My further suspicion is that the tapered, long, skinny bits that I use for 3d machining flex and unflex, and cause the issue and the need for more sanding. It could be machine flex also, but I cannot detect any of that.
Well, as usual I may have stumbled across a solution to a problem that no one else cares about...but here goes. If you create a vector of a regular shape, such as a circle, or an oval or a square around the irregular 3d shape, and click on the vector and the 3d model before doing the toolpath, the software will create a toolpath that goes continuously from one side to the other without the skips and the lines...or at least that's what my test indicates. The machining time increases, but I will sacrifice machining time to eliminate sanding time.