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Thread: question for lab managers....

  1. #76
    Rising Star
    Join Date
    Aug 2004
    Location
    New Jersey, Washington
    Occupation
    Dispensing Optician
    Posts
    91
    So from the information that everyone is contributing it seems that it is not an issue of the dispenser or the person in the lab finishing the lenses but unknown knowledge on the part of most people both on the retail sales floor and those doing the finishing in the lab. Finished polycarbonate lens edges whose matrix will absorb the chemicals(alchohols and others) of lens cleaners over time causes cracking and crazing of the poly matrix. If our industry, especially the people withing the retail establishments which have to answer to the public consumer giving them credable answers would ultimately cause a solution via informed seller and consumer. At this point most are unaware of the cause leaving sceptisism in the minds of the consumer and the frustration of the selling professionals. Maybe the Optical Labratory Assocations who provide finished coated lenses should provide a bottle when they sell orders to inform the optical practices regarding edge coating thier lenses with the same material they coat thier lenses with. Just a thought to keep relationships all round on better footing.
    Last edited by Jan Post; 07-22-2009 at 10:28 PM. Reason: spelling

  2. #77
    OptiBoard Professional
    Join Date
    Aug 2002
    Location
    USA
    Occupation
    Optometrist
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    408
    We still stock and use a large amount of poly. :( It's too much of a bargain for a large percentage of our market. Fortunately, we have eliminated the stress cracks in our own finishing process. They were far more prevalent two years ago when we still edged with a Optimax 401 and hand beveled with a single 800 grit diamond wheel. We also used poly for all the drill jobs that were finished by our outside lab. We never did our own drilling and have no plans to do so. Most of our cracks were in poly drill jobs and higher minus poly jobs that we finished with a heavier safety bevel. Oh, and they were more frequent during the late winter and early spring. Our outside lab advised us that they would no longer warrant poly drill jobs for more than six months which was a problem because we always provided a warranty for our patients of one year or more.

    One or all of these tactics led to the solution:

    1. We switched to high-index for all drill jobs.
    2. We replaced our edger with a reconditioned Kappa that came with new wheels.
    3. We replaced our hand edger with a cheap dual grit model. We do the heavier bevel first on the rough side and always pass to the fine side being certain to do a quick but consistent light roll across the entire face of the initially roughed bevel. Lots of water flows and it stays cool.
    4. We posted a sign in our dispensary for some time that read, "Just Say NO to Windex and Superglue - It Will Void Your Warranty" Yes, we actually did this for about a year and it really improved patient awareness of proper lens care.

    There have been no cracks at all in the last twenty or so months. I'm not convinced that the quality of the polymer has changed, or we're just working around the limits of any newer formulations.

  3. #78
    Bad address email on file
    Join Date
    Jul 2005
    Location
    Minneapolis
    Occupation
    Optical Laboratory Technician
    Posts
    66

    probally surface related

    I’ve made a lot of poly lenses and with many different processes. About six years ago we started a few of our labs in a cut to polish surface method. About a year into this I noticed that these labs did not have the problems that our labs that were using a fining process. I also found that when a lab had this problem they also had process variation that rendered less than 2/10ths stock removal. It is my thought that stress cracks come mostly from subsurface fractures at the lens surface and that the edging processes while it can contribute is not the main culprit. Partial validation can be found when looking at the % of finished lens with this as opposed to semi-finished that have these cracks.

    Hope this helps,

    Chris

  4. #79
    Bad address email on file
    Join Date
    Jun 2007
    Location
    Kansas
    Occupation
    Dispensing Optician
    Posts
    6
    Quote Originally Posted by MarcE View Post
    How are going to get the layout markings off with Dawn???

    BTW, I use denatured alcohol from the paint stripper section. Is that wrong? Stressful on AR?
    if the lenses have ar use tape it sticks to the in markings and pulls them off the lens. The problem with poly started to become big when they made poly opticaly better mainly for the use of blu-ray disc so now its opticaly better but a greater chance they will crack.

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