"Ten things it takes to turn edges"; resulting in the BC concentric with front curve.
1 True running lathe spindle collet with run-out of less than .010 mm TIR.
2 Validated Precision ground blocking tools.3 Blocking machine that can be validated for the minimum run-out.
4 Lathe software to turn edge profiles.5 Lathe tool bits that can turn edge profiles.
6 Center thickness control software to turn edges.
7 Effective center thickness gauging method( CT gage). Manual through arbor or blank thickness monitoring.
8 Lens blank arbors that allow center thickness measurement.
9 Conventional / transfer blocking. Transfer blocking eliminates precision lens blank requirement and improves optics. 10 Scleral lens are proportionately more sensitive to misalignment.