Eyehow – Eliminating Lens Edge Fractures

The Optical Journal - Optical News With Independent Views

I was recently talking to the Vision-Ease folks about today’s more sophisticated lens materials and how they can be affected by thermal or chemical stress, which may result in fractures. I thought this was a good subject to follow up so I asked several of our sponsors for some expert tips on Eliminating Lens Edge Fractures. They provided a lot of tips and so we are just showing some highlights. our sponsors are a great resource so please contact them directly if you would like more details on this subject.

Image Courtesy: Ralph Marco – President of Taylor Optical Supplies

 Jaysun Barr, ABOC, Santinelli International

  • Old stock/Inventory
    – Aged inventory not only loses its clarity (becomes yellow as you can see in the picture on the right here) but also seems to become brittle – I have experienced this recently identifying and completely eliminating the equipment as a variable. I have a client that bought some stock online and then the issue started happening when he had never had a single issue prior.
  • Worn vs New Wheel
    Franco Aluigi – Santinelli International

    Wet Edging Water Flow/Wheels
    – If running a “wet edger” it is essential to have appropriate water flow when/when not required based on material and where the edger is in the cycle.
    – Plastic/High Index – should have consistent water flow throughout roughing/finish/polish cycles.
    – Poly/Trivex –require completely dry roughing with intermittent wetting of wheels during the finish/polish cycle.
    – Also inspect the roughing wheel as part of routine maintenance. (See picture on the right).  Your results will only be as good as your equipment and condition.

  • Dry Edging Blade
    – If running a “dry edger” it is important to be running with sharp blades. Remember the “Ginsu” commercial? That smashed tomato is a fractured lens!
  • Appropriate Material Cycle
    – Know what you are working with and set up edger accordingly. This is more relevant to “wet” vs “dry” edgers
  • Chuck Pressure/New vs Old Tech
    – Many choose to use older technology to process todays slippery Super-Hydro coatings. Addressing this challenge the edger’s “Chuck Pressure” is often increased to maximum pressure. (a balance of improved final axis results + not “crazing” the A/R under the block being the goal). I see this being performed most commonly with older technology being used to process todays slippery coatings as a “this should get me by”

Matt Menzies, Technical Manager, Briot:

  • Slow down
    – Lens-edger should have a special mode that controls the speed of cycle by increasing the time the lens takes to cut-down to size.
    – Make sure you are familiar with your edger’s operations to properly configure the special cycles that help eliminate the potential for excess pressure.
  • Proper Size Blocks
    – Make sure you are using the proper size blocks and adapters to properly hold the lens and apply the pressure across the largest area possible.
    – Large lens/frame combinations are matched with the largest blocks and chuck adapters to get the best results.
    – Small frames require smaller blocks and chucks to clear the grinding wheels. Again, lens-edger’s configured for this ‘small frame’ type of job properly will take extra steps during the roughing cycle to reduce pressures on the lens that can cause fracturing.

Vision-Ease – Technical Tips

  • Frame Adjustment
    -Subjecting lenses to a heating medium while inserting or adjusting the frame can cause distortion and micro-fractures that may propagate fractures. Lenses mounted tight or with localized stress can also cause fractures.

Please let us know if these lens edging tips are helpful, we have more to share!