What are folks using when filling semi-rimless frames with minus scripts? Stock 1.67 at 1.0CT is too thin for grooving and surfaced 1.67 looks almost as bad as CR-39. If a patient insists on semi-rimless, is poly the only cosmetic choice?
What are folks using when filling semi-rimless frames with minus scripts? Stock 1.67 at 1.0CT is too thin for grooving and surfaced 1.67 looks almost as bad as CR-39. If a patient insists on semi-rimless, is poly the only cosmetic choice?
You should be a little more specific. Thickness depends on power and eyesize/decentration.
You can surface a 1.67 with enouph edge thickness to look good, while still looking better than platic. Poly is nice for not chipping. Trivex is nice but not at high minus.
It all depends. If the frame is centered properly a high minus stock 1.67 should be fine.
Essilor had a promotion one day where they gave us a pair of 1.67 D Alize's and give us the right lens for free (so half off). Always, what ended up happening is that I was getting the 1.67 D Alize with that promotion in a progressive (Panamic, Comfort, or Ovation) for cheaper than the CR-39 price. So when that promotion came around it made sense to offer it at the cheaper price, so I did a few 1.67's at a -1.00 and +1.00 (with a 2mm edge of course). I found that 1.67 is my favourite material for grooving. Even on the very thinnest I found that the flat front helped it go through nice and easy and when done it was a very clean groove.
Just because you can grind a material to a thin center there is no law that says you have to. If the edge is too thin, beef the center.
Why would a 1.67, surfaced lens, end up looking like Cr-39? Typical minus CT for CR is around 2.1mm, while a 1.67 can show somewheres around a 1.5mm ct. All other things being equal (base, aspherical/spherical front, power, etc.) they should not look the same.
Most labs use fairly complex computer systems to figure the required edge thickness for grooved lenses - regardless of power. If a 1.0ct stock lens is too thin - which it certainly can be on weak minus... grind the lens. The computer system should calculate the thinnest CT (on any material index) to produce a groovable edge point.
If your current lab grinds a 1.67 material that ends up looking like a CR-39 of equal power, talk to them about it.
J. R. Smith
Let's say up to a -5/5.50, 48 eye with 1-3mm decentration.Originally Posted by mrba
Our lab won't grind 1.67 that thin. Perhaps the answer is to think about other sources when stock isn't an option?Originally Posted by JRS
First I can't imagine that a pt would pay the high price of a 1.67 alize` lens in a low minus power, and assuming they had some reason to, most any minus rx with a 1.50 ct is going to be think enough to groove, unless it is quite a shallow b or a lot of decentration; we have an advantage here in that we have a National Optronics 6E that has a goover in the unit, so no sweat. grooving those thin lenses on a hand, auto-groover would be tough, but that why we upgraded to the 6E four years ago, saved us a lot of lenses...
Texas Ranger,
Unfortunately, a number of the frames are shallow. We retail Seiko 1.67 SV at $160 SRC $245 ARC; is that low? Of course, everyone who wants a rimless frame expects the lens to look like the demo no matter how much you tell them it won't. Most say that's fine then flip out when they get them.
Jo,
Our lab is surfacing 1.67 to 1.2 CT unless it's a short 'B'. When it's a shallow frame it's sometimes necessary to beef up the CT in order to get a 2.0 minimum ET for nylors.
I also like the Indo Superfin 1.52 for nylors and 3-piece mounts when thickness isn't an issue.
Dottie
We got a new santinelli with the auto groover, What a gem that has been when grooving that 2.0 edge thickness or lower.
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