Crizal Avance + Poly = Lens cracking issues?

[becc971]

Anyone running into this?

[Sphinxsmith]

Stock or Surfaced?

cs

[Tallboy]

Be very very careful in sizing thin center lenses and crizal coatings. Go small, match bevel to frame as close as possible. If you need to heat the zyl to insert the lens, it is too big, probably in the b dimension. This will flex lens and stress cracks occur.

[becc971]

Stock or Surfaced?

cs

we've actually had 2 jobs do it, one stock one surfaced PAL

Both came from the lab initially, VSP jobs.

[Chris Ryser]

Just keep in mind that Polycarbonate is a very flexible material and the AR coating is made with SIO2, which is glass and much less flexible.

A pair of glasses in pockets or purses can be under pressure, or on the face, temples not opened enough, can also produce pressure and crack the coating.

[jefe]

Crib the lenses so that the lens doesn't flex as much as it's feeding into the roughing wheel. Also, use the largest blocks and chucks you can for the job.

[Sphinxsmith]

We were having the same problem but mostly with stock lenses. Had to remake with grinders a few times to get around it. Frustrating.

cs