Well here is your chance to make lemonade out of lemons. I have had lucite lenses for years for laboratory safety, but I am sick of the bifocal "line". The answer is to now get omnifocals made out of lucite instead of glass. I rely on the lucite lenses when using the grinder and I know metal flakes have hit the lens several times. The lucite does scratch but will take quite a beating without breaking. Whatever the reason for the crack, it does look like the crack goes along the bifocal boundary. My next set of lenses will be the kind that has a rounded transition between the two ranges and in lucite.

Don Shillady
Retired Scientist/teen rodder