Sherical generation is a useful technique for a range of problems
or projects.  In this case, these are tools for making lenses.  
Oak Engineering, UK very generously allowed me to photograph their
process.  One of the revelations is that shop adaptation of a standard
BP is more accurate and facile than a couple very expensive European
purpose manufactured machines which are now relegated to storage,
or used for rough end work in the preliminary shaping phase.