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Thread: Transition lenses

  1. #1
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    Confused Transition lenses

    On transition lenses I've noticed that there is a tendency for me to get waves. Not all the time but too often. I use a Vista dry generator and was wondering if it was the heat generated from the generator that caused the waves. It isn't every time by any means but it is often enough to be agravating. I let the lens cool for at least a half hour after blocking. I would be grateful for any cures for this problem!
    Thanks Tom

  2. #2
    Master OptiBoarder Jeff Trail's Avatar
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    Tom,

    From one lab rat to another the problem is more than likely in your blocker not your generator :-) ... Even if you are letting the lens "settle" for a half hour, the damage was done already by the temp. shock of the blocker.. if I were you I would double check the blocker temps and work back from there. A transition does not "act" like other materials that will settle down after blocking because in the majority of the Transitional material the chemical is imbibed through the front surface and NOT through the total lens.
    If you find that the temps are higher than around 122 or so than you will see a nice little circle on about every lens at the outside of the ring of the alloy.. you might want to use a larger size block if you do not want to tinker with the temps of the blocker.
    I run my blockers at 122 in the stem and 118 to 119 in the pot and if we are running a transition or spectralite and it has been a while since we blocked we will even give a fast spurt to clear the stem just in case the temp has risen slightly.
    All I can say as we have zero problems with any of the transitions or the spectralites (which for some reason a lot of labs have problems with in the power)
    I run both dry and a wet generator and have no problem with waves.. as I said I would start with the blocker and go from there, and since you only mentioned Transitions as being a problem I wouldn't think of looking at the generator or cylinder machine yet. :-)
    If that does not work let us know and we'll try to figure more things out. BUT I still think that blocker is the guilty culprit.

    Jeff "maybe spent to much time in a lab" Trail

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    Big Smile Thanks!

    Thanks Jeff!
    I'll look into the blocker temp. I know that when it jams or runs slowly some people turn the temp up to get it running agian. so that could be the cause of the on and on problem.
    Thanks agian!
    Tom

  4. #4
    OptiWizard
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    Just want to add that the Transitions 1.56 stuff is M U C H more heat sensitive than the 1.50. Jeff's comments are right on, basically, when you have waves, start with the blocker.

  5. #5
    Master OptiBoarder Jeff Trail's Avatar
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    Jim,

    You talking about the Sunsesnor's? I haven't found that as a problem .. hmm.. the one problem I did have is that when it first came out the guys sent out a "facts sheet" and the recommendations they gave were WAY off on how to run the lens, and we were having them crack all over the place at deblocking.. once I had everyone slow the sweep speed than I have not had any problems at all and run them like every other job, other than that sweep speed. I finally got a hold of a guy at S.A. (an engineer) who knew what the **** he was talking about and got some info on the material and the structure of that material and got an understanding on why you need to do a very slow sweep when generating :-)
    How about those Trivex .. you run many of those yet? I liked it and the end product was a dream after fighting those stinking poly's. It felt like a poly while cutting, ran on poly pads but to take that lens wipe it off and pop it into the lensometer and check it and than think "****.. I forgot to watch for scratching" and than hold it up and see ZERO scratches!! ..Oh my that was almost like hitting the lottery.
    Now if they would just come out with more product line and make the prices just a little closer to poly I would be very happy..

    Jeff "grind'em if ya got'em" Trail

  6. #6
    sub specie aeternitatis Pete Hanlin's Avatar
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    Other than to agree with Jeff (and point out that almost every lab runs the alloy too hot ;) ), I'd just add that even the regular "plastic" Transitions material is not really CR-39. If memory serves, the material used for "plastic" Transitions is CR-309, or something like that, and I think it is actually a bit softer than ordinary plastic.

    Another trick I've used with varying success was to chill the lens before blocking it up (using a cooler filled with ice water... of course, you'll get tired of maintaining such a cooler after a few days ;) ), or double taping the lenses. If you feel like spending a lot of money on the problem, you could also look into getting a non-alloy blocking system, like the Step One by Gerber- which uses a wax-like substance. The additional advantage will be that you will avoid any alloy-related OSHA or EPA problems if you are ever inspected.

    Pete
    Pete Hanlin, ABOM
    Vice President Professional Services
    Essilor of America

    http://linkedin.com/in/pete-hanlin-72a3a74

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    Big Smile Wax system

    I agree Pete that the wax system is the way to go. I tried turning the heat down on the blocker and the alloy inside formed a frozen pond. Hard on the top and liquid underneath. I,ve seen the wax system at the Cole lab before what temperture does the wax melt?
    Tom

  8. #8
    Master OptiBoarder Jeff Trail's Avatar
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    Tom,

    Are you using a 99 blocker? If so they are very hard to get adjusted but once they are they work great. If you are running a 99 blocker you might want to check to make sure both the stem heater and the pot heater are working, a lot of times people tend to over look the stem heater and than try to push the pot temps up to keep the stem flowing.. a NO-NO if you don't want heat problems.
    Now as to wax, oh it's OK, I have run both but still prefer the 117 myself, I didn't find it cost effective to swap over, it was going to run around $12.5, and I didn't like having to cut everything on center. I do a lot of low vision high prism work and this was going to be a nightmare getting lens to cut out.
    For you the wax maybe the way to go, for Pete it maybe the way to go..for me? nope.

    One thing is getting the right temps adjusted, another is have a good thermometer to check it with and make sure you put it into the alloy and shut the lid for a few minutes to get a good reading.. you would be amazed how having the majority of the thermometer sticking out of the alloy and in the air conditioned air will give you a false reading.
    The way I set mine is on, I turn both down till they are set hard, than start ticking them forward a very small amount, I just watch the lights and soon as the come on telling me they are heating I stop, I let it heat till the kick off, check it and turn it till it clicks on again.. it takes a good hour to do it but once it is set they hardly ever go out of whack.
    I would check the stem heater first to make sure that is functioning, and try it that way before dumping $15 grand into a brand new system :-) ....
    I guess it may depend a lot on if it is your money or someone esles cash going in the the equipment on what to do. I have 3 99 blockers and am happy with all 3 ... I like that sales point of "not needing tape saver no more" and than found out that you still do more often than not when using the wax system.. I know of 6 other lab owners who went through that problem :-)
    Just need to weigh the pro's and cons before running out and buying something that costs as much as a car ... sounds like you just were a little heavy handed with adjusting, this is one of those times where it takes time and a valium to get you through it :-)

    Jeff "wish I could win the lottery and retire" Trail

  9. #9
    OptiBoard Professional RT's Avatar
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    gebe33:
    The "wax" in the Gerber Step One melts around 110 degrees, but is usually injected at 128 degrees. But don't confuse "temperature" with "heat". They are different beasts. The wax has very little heat capacity, as opposed to the lead-cadmium alloy which has a tremendous amount. Go ahead, stick your hand in the alloy pot--it burns like h*ll. Stick your hand in the wax pot--it won't even feel hot. If your hand doesn't feel the heat, the lens won't either. Instead of coming up with elaborate ways to get rid of the heat, follow your instincts and look at a system that doesn't put the heat there in the first place.

    As far as Jeff's other thoughts on wax vs. alloy, the thinking is certainly out of step with most modern labs. Many labs can and do use the Step One blocker day in and day out without taping lenses. Some labs can't or won't make it work--apparently Jeff is in contact with all of them. Oh well. Off- center blocking? Who said Step One can't? Besides, with modern computerized generators, its far less of an issue. And it takes an hour to measure the temperature in the blocker??? That's something to brag about???

    With many alloy blockers, the alloy is injected through a hole in the block into the cavity between the lens and block. Even with great technique, the alloy will sag slightly at the injection hole. The old Coburn blocks had removable fining centers that also caused the alloy to sag slightly. You could always look at the block through the lens and see exactly where the fill hole and fining centers were. With the dinosaur sweep generators, that wasn't a problem. However, with single point generators like your Vista, the lens deflects slightly into those areas of weak support during generating. You get aberrations at each. Soft materials like Transitions or thin materials like Poly are more likely to show the problem than CR39. Check for voids in the support surface--it might not be heat, but uneven support that's the culprit. That's a reason why Gerber works so well-- the wax is injected from the side, giving a uniform support surface for the lens.

    Check the vacuum you're using on the Vista. The primary means of cooling the machine is through the air flow to the vac. Too little air flow, and heat inside the generator could be the problem. That might show up when you're busy, and go away when you're not, which could explain the intermittent aspect of your problem. Dull cutters also make more heat than sharp ones, so check the condition of the cutter. Oddly, you'll get better cutter life with fewer but deeper cuts--it seems backwards, but it's true.

    Last idea-- check the calibration on your generator by cutting a sphere (-10.00 or so), and fining it for 5-10 seconds. Ideally, you'll see roughly equal fining across the entire surface of the lens. If you see distinct patterning, like concentric circles, the fining process will be pushing a wave across the lens. Single point generators have the strange property that when they're not calibrated correctly, they cut non-spherical and non-toric curves. When a sweep generator is miscalibrated, it just cuts the wrong curvature--either too steep or too flat. Its possible that the waves are a result of poor calibration on the Vista. Again, softer materials may be more susceptible to showing this type of problem.
    RT

  10. #10
    RETIRED JRS's Avatar
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    Very nice response Rick. I do believe you covered most of the items. Voids/air pockets in the blocked surface are a real problem on single point generators.

    The only thing I would add references the use of tape on Step Ones. Some labs have gone back to taping to reduce the amount of cleaning efforts when de-blocked. AR and backside coatings don't like the wax very much. And as I seem to remember a similar thread on 'cleaning' where you mentioned 'no need to tape then either' I tend to agree in theory. Quite possible to do a good job cleaning without tape, but a hard sell.
    J. R. Smith


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    Thanks RT!

    I'll look into your sugeations.
    Tom

  12. #12
    Master OptiBoarder Jeff Trail's Avatar
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    RT,

    Thanx for the insults :-), BUT I tend to look at it from a number of views, first I am own a wholesale lab and what I do tend to be different from a retailers lab or a central lab for retail where they might not be running a LOH V75 or better :-)
    Next, the name of the game when you OWN a lab is to save money where you can because of the low profit margin now a days in the wholesale market.
    Last but not least I do a good amount of specialty work so you don't know what works in MY lab, I even have an old 108 I use once in a while for those bi-convex and dive mask stuff I do.. not every new pc. of equipment is always the best in every situation.
    As for the last "shot" you took at me about knowing every lab owner who didn't know what they were doing, I know a lot of lab owners come to think about it the lab group I belong to was Essilor's largest private customer last year so I guess we do know something about grinding a lens or two :-)
    I might not be a "super" lab but I know I'm happy owning a lab that does those few hundred pair ... better to own than work for the "man" and tell everyone else how behind the times they are ...
    As JRS said you jumped into the other thread and commented as well I guess on how dumb they were as well for using tape on the one step, but speed is the name of the game in wholesale.. if I have my guys in there washing and washing and messing around with a lens for AR coating than it costs me money.. use tape and the time saved more than offsets the cost.
    The way you tossed the insults around and touted the one step you wouldn't happen to be an employee of Gerber/Coburn would you? :-)
    In closing the "state of the art" labs you talked about are the minority not the majority in the industry, they may do the majority of the work but they are fewer in number than us mid size to small size labs...you have a lot of mid size labs out there not running a LOH V100 or better just because the volume is not there to warrant it.
    Oh and if you did stick your hand into an alloy pot and it did "burn" you than it is to HOT...if you have it set correctly than it does not feel any hotter than bath water.
    I can see now we won't agree on much, that's fine by me. This is my last contribution on this thread, just wanted to help the guy out with his EXISTING system not telling him he needed to go out and spend $15,000 to get it fixed. Unless he is getting $ that in wages an hour and his breakage is costing him that in a month or so than it maybe worth "spending" an hour to fix the problem (yes MAKING and SAVING money is something worth, as you put it, to brag about)
    Amazing how you can get two opposing perspectives to the same question :-) To me a good lab man is going to get the best production out of what he has to work with and do it CORRECTLY. I don't come to this board to get into pissing matches so I'm done with this thread, so feel happy to reply with more insults, I come to maybe spread a little bit of help when I can and to shoot the breeze with other people in optics, not to waste my time with personal insults. Have a great day. :-)

    Jeff "just some dumb out dated lab rat..or according to some people.hmmm" Trail :-)

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