These were all done with the 48V 400W DC spindle on the Shapeoko. I also did all the anodizing in house. The VFD spindle can run from 0-24,000 RPM or just about any speed in that range. They are massively quieter than the trim routers and very powerful. The OKO (and X Carve) by the nature of how it is built is not meant for fast deep and deep cuts like a ball screw mill is built for. Things like belt stretch and frame twist come into play more than the spindle powder over all. Pushing the mill so hard that the spindle stalls will warp the frame and or stretch a belt out of calibration for the cut. My main reason for going with the VFD was the noise and speed range options for slow speed things like acrylic and such. I mill everything from acrylic and PCBs to aluminum and stone work. But by far I do most of my work right now in aluminum.