When is it worth the extra time and effort to make a 3D roughing path vs just cut the smooth 3D finish path?
I get the idea. If you are making something with fine details, cut out the larger chucks with a quarter inch bit, and then swap out to a smaller bit for the details. Less wear and tear on the smaller bit. Maybe switch to a ball nose bit if that is needed.
But, if I am using the same bit to rough cut as I am using for the finishing pass is there any advantage to making two separate paths? In that situation all it seems to do is add time and complexity.
What am I missing? Is there an advantage to to switching from a flat bit to a ball nosed bit when making the finishing path?
In my situation I am not making art, I am trying to figure out a way to quickly batch out parts. I need to balance speed and precision while minimizing tool changes.
You get more precision when the tool is not hogging out a lot of material. Remove the bulk of the material quickly with a rough pass, then remove a small amount with the longer finish pass, resulting in less deflection, chatter, and a smoother cut.
The 3D Finish is all done in one pass. The 3D Rough is done in multiple passes, each pass deeper by whatever you set as the DOC, depth of cut.
If your 3D project has little enough relief that the bit you are using for finishing can comfortably handle a DOC equal to the height of the relief, no problem eliminating the 3D Rough.
But for most work you need the multiple passes of the 3D Rough operation to leave less material than the DOC your finishing bit is capable of.
As Tod has stated, trying to hog too much material in one pass is asking for trouble.
I would think using a larger tool at a deeper and fast rate, even with more passes would be less time then would the smaller bit at the slower rate. I would be worried about breaking the smaller bit with the DOC needed to do it in one pass.