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A number of the so called 2.5D cam programs also offer some 3D capability. Both my DesKAM and EstleCAM can produce 3D toolpaths from STL files. EstleCAM offers both raster and waterline tool paths and seems the more capable. I have not yet fully explored the EstleCAM capabilities. However I have tried raster mode machining using other software. The Raster mode is best used for low relief (bass relief) objects as shown below. I needed to use a very low feedrate because I only had a 2,000RPM spindle at the time and was using a 1.5 mm ball nose cutter. The X, Y movements were no problem but the Z-Axis was clearly suffering. The 8.0 Kg head and spindle were going up and down like a woodpecker. The waterline mode will be much gentler of the Z-axis and may be useful for deeper objects. I have yet to give it a try.
I have been a model engineer for over 50 years and built many engines of all types before acquiring a CNC mill. In the last ten years I have had more fun using the CNC mill than I can say.Mike
Jim. F360 has various finishing options, something like RAMP will work out it's way around a shape while constantly lowering the tool not even stopping and starting at each height and would actually be a better option for something like the moulding that you describe than one where the tool is going up and down all the time, infact I would think even scallop would tend to mostly run along the moulding rather than up and down. You choose the best option for the job or feature. Or you can use a simple contour which will produce a similar path to what you and Mike describe doing manually by working out the path it needs to follow at any given height increments and all the time moving the head down for the next increment. You can split any curved surface up into a number of sections and use different vertical steps as the curve flattens out or becomes steeper. You do need to decide on these sections Manually unless paying for the "Steep and Shallow" option which even works that bit out for you.