Finishing 3D surfaces with a 3-axis machine and a ball end-mill can be challenging. In a single op, you can have the ball engaged near the tip where the SFM is much lower, and other times engaged near the side where it behaves more like a straight endmill -- and anywhere in between. If you run the speeds/feeds calculation for these 2 scenarios, accounting for chip thinning, the spindle-speed and feed-rate can be wildly different for tip cutting vs side cutting, and can result in poor surface finish in some areas. For example, using a 2-flute, .250" ball end mill at 980 sfm with a .002" ipt chip load, and a .020" DOC (axial and radial): When the endmill is parallel to the surface (cutting with the side), I get a 15,000 rpm spindle speed, and 111 ipm feed rate. When the endmill is perpendicular to the surface (cutting with the tip), I get a 27,500 rpm spindle speed, and 204 ipm feed rate. A workaround is to use the "slope" function, or tool path containment to limit how far up a ramp the cutter is allowed to go, but sometimes that results in a noticeable line on the finished part where the 2 ops meet. It would be awesome if Fusion had a way to dynamically change the spindle-speed and feed-rate based on this angle of engagement. For ball-end mills, it should be relatively simple sine function. You could implement this for other endmill geometries also, but the calculation would be more complex. What I'm suggesting is a little different than what was posted here, which was for variable speed based on depth of cut.
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