Just a question,
I spoke with my lab today and they said that they can't surface trivex to 1.0. There rationale was that it easily waved and had power issues at 1.0. Sounds alot like the poly issues we used to face surfacing to 1.0, but it is done every day.
If trivex has a lower index, and has to be ground 0.3 mm thicker, that would seem to reduce the number of patients we can offer the trivex to. Just an observation from an annoyed proponent of trivex.
Why not 1.0?
AA
Fda ??
Provide an Rx and lens type.
CT will range from 1.0-1.3 on minus powered TVX lenses. Same goes for poly (save your breath poly hunks, unless you run a surfacing lab (especially those that do AR coating) I don't want to hear it.
Also, mentioning the lab name wouldn't hurt. Some labs tend to through a lot of misinformation out there about products that they do not manufacturer.
Adam
I asked about the new Trans Trivex ST28, but they seemed to imply that all Trivex should have a min of 1.3 mm.
AA
No way. It would pass any drop ball, and last I heard Trivex was considered a high impact lens material in the same category as poly by ANSI in regards to minimum thickness in safety glasses.Originally Posted by Jacqui
AA
When surfacing any material to a 1mm thickness there can be a number of variable that would allow one lab to do this to 1.0mm and another could only obtain 1.3mm. That is assuming they both will want to have good optical quality at the center.
The type of cutter used is critical.
The type of blocking material used.
The thickness of the blocking material and diameter of the blocked surface.
Any of the above to name a few could require one lab or one piece of equipment to not achieve the same results.
Like Adam of Cherry Optical implied, there are many opticans at the retail level who are making assumptions without taking into account all of the variables.
As with any industry unless you have worked in the particular field and actually performed the work being done it is quite easy to draw conclusions that when examined by an expert in that area can show you where you made incorrect assumptions.
So Trivex optimized in production maybe able to be surfaced at 1.0mm but in some labs they are only willing to take the rate of re-making the lens if they process at 1.3mm.
What a lab never hears from their customer is "Make it at 1.0mm even if you have to waste 9 pair of lenses to get one that is excellent, and don't worry I'll pay you for all 10 jobs"
Look at all of the dynamics of a situation and usually there is a logical explanation. This specific flat top issue could have something to do with the
thickness in the flat top area, although I am not specificly familiar with this Trivex flat top lens.
I can appreciate that, but I spent the better part of the last 12 years in some facet of surfacing, including 2 years as a surface manager for a wholesale lab...and we surfaced a fair number of trivex lenses in my stint as a dept manager...but your point is taken.
I was hoping that the reason would be the manner in which this particular product was imbedded with the transitions, such as if the 1.0 CT would cause the middle of a minus lens not change because it was surfaced out.
AA
I can understand the issues related to grinding below 1.3, although .3 mm difference in thickness is pretty minute. Theoretically, the material is so strong that I could see them eventually getting it below 1.0 (maybe with custom molding), since the material is so strong. I tested one in my garage on an anvil and had to hit it pretty hard with a hammer to break it (am thinking of applying for a patent for my testing method). Anyway, I'm finding they are GREAT for plus and low minus up to about -4.00. Above that they get kinda thick, unless the frame is small. I LOVE them for rimless.
One expansion on my comments:
Regarding the difference in machining methods, this can determine minimum center thickness.
The speed and feed rates of the cut on a thin lens as well as the blocking can be an issue.
For example: I would think that wax blocking and fast speed and feed rates could cause the material to have undue stress at the center. The feed rate would be the most critical since near the center the speed of contact point of a single point cutter is zero RPM, resulting in no material being cut. Center point issues in lathe type machining. If the cutting process is not lathe type but more of a flat mill cut across the lens this would cause the same problem.
This problem near the center of a lathe cut will become more visible if the cutting tool is near the end of its duty cycle.
Since you have worked in surfacing ask the lab that quoted you a minimum of 1.3 center thickness what generator they are using. You could then call the equipment manufacturer and confirm what the generation reason might be.
But like I mention before it may just be the policy of that lab to minimize rejected jobs.
Trivex trans. is a very flexible. Surfacing to 1.0 center on low power Rx would cause the lenses to bend easily. This fact is worse in smaller frames since the edge is extremely thin. I would not recommend a thickness under 1.3. We have made thicker Trivex trans. (1.5) over because accounts do not like how easily the lense flexes.
Joseph Felker
AllentownOptical.com
100% TRUE!:cheers: Even though the material could, theoretically, withstand an impact with a 1.0mm ct it could comprimise the optical quality. It is a soft material and will bend and flex and could cause permenant warping. An additional .3 to .5 mm ct wont make the lens look too thick. Most people could never tell the difference. But it can add some important structural support. In the case of a higher power lens I think that they can make the ct much thinner, the added edge thickness can add to the structural support needed. Lower power lenses do not have the 'benefit' of the added edge thickness for support.
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