Fast tool servo (FTS) in ultra-precision diamond turning is an efficient technique for high-precision fabrication of freeform optics. However. the currently adopted constant scheme for control point sampling takes no account of the shape variation of the desired surface. which might lose some micro features and result in low form accuracy and non-uniform surface quality. https://www.roneverhart.com/Western-Digital-Ultrastar-DC-HC530-WUH721414ALE6L1-0F31170-14TB-7-2K-RPM-SATA-6Gb-s-512e-SED-3-5in-Hard-Drive/