Cheap 4th axis tear down and re-grinding

I bought a cheap 4th axis from China, and combined it with a 1kW AC servo motor (also from China). The result is a super fast 4th axis, that can do precise positioning for 4-axis milling and indexing, and also reach 1000 RPM for turning operations. But how good is a $150 spindle mount? In this video I measure the run-out, and improve it by regrinding the mounting cone on the CNC mill.
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