Hi, quick question.
Would there be any difference in calculating speeds and feeds for ball nose endmills vs. flat endmills when cutting the same material?
It…depends. On what your are doing with the ballnose.
One of their typical uses is to do 3D finishing passes on a surface after a 3D roughing pass (usually done with a square endmill), and in that situation there is little material left to remove, and you can go much, much faster than you would for a regular cut.
And then again is for some reason you would like to use the ballnose to remove a significant amount of material, e.g. pocketing (hint: don’t), then you would probably fall back to feeds and speeds similar to that of a flat endmill, BUT probably at a lower depth per pass, if you don’t want to get in trouble. And then if y ou are taking really shallow passes, you can them be a bit more aggressive with the feedrate/RPM combination.
If you tell us more about the scenario you have in mind for using that ballnose (what diameter by the way?) folks will probably be able to provide more specific tips.
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Mainly interested in 3D passes.
Let’s say 1/4" flat end mill to rough, 18000RPM, 116IPM, leaving 0.04" radial stock and 1/4" ball nose to finish. My thought would be to leave the speed at 18000RPM and adjust the ball nose feed to account for a 0.04" stepover, so maybe 147IPM. Would you say that’s an ideal approach?
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Oftentimes, the 3D finishing passes will cut “through” the steps left by the roughing pass, not along them (it all depends on your CAM), so the amount of material left to cut for the ballnose will not really be a matter of stepover then, but more like a depth per pass. And then it’s not a matter of chip thinning at low stepover, so the math for increasing the feedrate is not so direct. I would just…experiment, starting with the same feedrate as for roughing, and then using feedrate override during the cut to incrementally push it higher and find the limit.
Great advice. Thanks for the suggestion!
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