I’m kinda new to this whole machining thing, so I hope you can correct my dumb assumptions.
Why is higher rpm better? I’ve been doing a lot of research on speeds and feeds for aluminum on a Shapeoko and something odd I’ve found is that people run their spindles at really high speeds for rather large tools.
For example, @Vince.Fab says that he runs his spindle at 20-24k rpm. However, from a bunch of articles I’ve read, it seems that sfm is directly proportional to rpm and diameter. Some sources say that if your rpm is above the rated sfm of a material, you could generate excess heat and wear down your tool quickly. According to
surfaceFeetPerMinute = rpm * cutterDiameter * pi/12, if you were to run a 0.25 in diameter endmill at 20k rpm, the surface speed would be around 1300 sfm. That is around 4 times the rated surface speed of 6061 T6 aluminum, 330 sfm (!?!). I’m confused. What am I missing here?